This section contains all GERSTEL Application Notes. Due to the large number of these publications, please use the web site search function found on the home page to quicken your search. To view all application notes, select "All Application Notes" from the "Applications" drop down menu.
Keywords: Impurities, Industrial Products, Capillary GC/MS, PTV Injection, Multicolumn Switching, Multidimensional GC
The separation and identification of trace components in industrial products is a well known analytical problem, particularly if they elute in low concentrations close to the major component. Current methods fail due to insufficient resolution and or the detection limits of existing systems. In this paper the potential of a combination of programmed temperature sample introduction and dual oven multicolumn switching for the determination of trace impurities in industrial intermediates, is discussed and demonstrated on three examples. It will be shown that a reliable identification of trace amounts of impurities in these industrial products is possible, with a fully optimized multidimensional system, without interference of the major components.
Keywords: Capillary Gas Chromatography, Mass Selective Detection, Multidimensional GC/MSD System, Furan Fatty Acids, Fish Oil
The separation and analysis of very low concentrated furan fatty acids and other minor component fatty acids in complex sample matrices, such as fish oil or lipids derived from liver and testes, require several pre-analytical separation steps in order to obtain sufficient resolution in single column gas chromatography: after extraction and transesterification hydrogenation, urea complex precipitation and Ag+-TLC were applied prior to GC-analysis of furan fatty acids. By using a multidimensional GC/MSD-System with cooled injection and flow controlled column switching with cold trapping in between, it is now possible to identify directly the methyl esters of furan fatty acids without any further pre-analytical separations. The most common of the furan fatty acids can be subdivided into two groups, bearing either a propyl or a pentyl side chain in the 5-position of the furan ring. In addition to the known eight furan fatty acids in fish oil, six new ones were identified, four with a propyl and two with a pentyl side chain. Four of them were reported earlier to be found in the hepatopancreas of crayfish and in fish tissue, whereas the propyl group 16,19-epoxy-17,18-dimethyldocosa-16,18-dienoic acid and the pentyl group furan fatty acid 6,9-epoxy-7-methyltetradeca-6,8-dienoic acid are hitherto unknown ones.
Keywords: Direct Thermal Desorption, Volatiles in Soil, PCB´s and PAH´s, Trace Analysis, Capillary GC/MS, Cooled Injection System CIS, PTV
Thermal desorption is a well known technique for the analysis of volatile organic contaminants in air and normally employs adsorption on porous polymers. This operation principle can also be adapted for the direct thermal desorption of volatiles within a wide boiling range directly from soil samples. In this paper the potential of a newly developed thermal desorption system for direct desorption and analysis of volatiles from soil samples is discussed and demonstrated. It will be shown that the combination of thermal desorption with an intermediate cryofocusing step in the inlet liner of a cooled injection system (CIS/PTV) is a reliable and fast method for the determination of volatiles even with such high boiling points associated with PAHs and PCBs
Keywords: Capillary Gas Chromatography, MultiPurpose Sampler, Headspace, GC/MS, Volatiles, Urine
A MultiPurpose sampler (GERSTEL MPS), designed for liquid large volume, gaseous and headspace samples was tested for its suitability in the GC/MS analysis of organic volatiles in human urine. Headspace sampling with a volume, temperature and speed controlled gas tight syringe was combined with a temperature controlled cold injection system for cold trapping, enrichment and focusing of analyte. Regular 2 mL GC vials filled with 1 mL urine were used as headspace sampling vials. A 100 vial autosampler tray was equipped with an additional temperature and heating time controlled pre-heating module for 5 vials. Preliminary experiments were done with urine samples from our clinical laboratory with a ketone or glucose positive test result. In addition urine samples from healthy volunteers were taken and analysis were done with and without acidifying the urine. The promising results in regard to sensitivity and practicality in a day to day routine together with the cost cutting philosophy of a MultiPurpose sampler makes this highly automated system very attractive for clinical routine use.
Keywords: Capillary Gas Chromatography, Mass Selective Detection, Multidimensional GC/MS, Nutritional Oils and Fats, Fish Oil, Furan Fatty Acids
ABSTRACT Identification of furan fatty acids as minor components in oils and fats require several pre-analytical separation steps in order to obtain sufficient resolution and sensitivity in single column gas chromatography. After extraction and transesterification hydrogenation, urea complex precipitation and silica gel column chromatography or Ag+-TLC were applied prior to GC analysis. By using a multidimensional GC/MS System with cooled injection and flow controlled column switching with cold trapping in between, the methyl esters of furan fatty acids can be identified directly without any further pre-analytical separations. Butter, milk and ten nutritional oils were investigated. Different transesterification methods were used for the characterization of the oils and compared with each other. Electron impact and chemical ionization were applied to identify the fatty acid methyl esters by GC/MS. Fourteen furan fatty acids were identified in fish oil, two in butter and one in milk. The same furan fatty acid were found in peanut, thistle, sunflower, hazelnut and olive oil, whereas none were detected so far in sesame, corn, walnut or grape seed oil.
Keywords: Capillary Gas Chromatography, Natural Gas Analysis, Multioven Multicolumn Switching System, DIN 51872.T5
In this paper we focus on the design and evaluation of a natural gas analyzer that meets the demands of a preliminary draft of the standard DIN 51872.T5 of September 1992 for Germany. The dual oven, multicolumn GC system allows the simultaneous analysis of permanent gases such as helium, hydrogen,oxygen nitrogen carbon dioxide and carbon monoxyde and hydrocarbons with 2 up to 8 carbon atoms, within 40 minutes. The analyzer consists of two independently operating GC systems. Their series coupled sample transfer line permits the simultaneous purging and introduction of both samples in the respective systems. The sample introduction is performed by gas sampling valves equipped with a sample loop. Permanent gases, CO, CO2, as well as methane and C2 -hydrocarbons are analyzed in the first GC, by means of two capillary PLOT columns. The column switching device in between these columns consists of two multiport rotating micro valves. The detection system is a series coupled combination of a low volume thermal conductivity detection (TCD) and flame ionization detection (FID). A methanizer in between both detectors allows simultaneous TCD and FID detection of carbon monoxide and carbon dioxide.
Keywords: Capillary Gas Chromatography, MultiPurpose Autosampler, Headspace, GC/MS, Volatiles, Urine, 4-Heptanone
A MultiPurpose autosampler (GERSTEL MPS), designed for liquid large volume, gaseous and headspace samples was tested for its suitability in the GC/MS analysis of organic volatiles in human urine. Headspace sampling with a volume, temperature and speed controlled gas tight syringe was combined with a temperature controlled cold injection system for cold trapping, enrichment and focusing of analyte. Regular 2 ml GC vials filled with 1 ml acidified urine were used as headspace sampling vials. A 100 vial autosampler tray was equipped with an additional temperature and heating time controlled "preheating station" for 5 vials. Profiles of organic volatiles were determined and 4-heptanone as a ketone of medical interest presumably related to diabetes was quantified. Calibration curves and imprecision of the method for 4-heptanone concentrations in the range from 40 to 800 ng/ml showed a correlation coefficient of r = 0,999 and a coefficient of variation (CV) between 3.0 and 3.4% respectively. In this pilot study including 51 patients with diabetes mellitus (Type I and II) and 42 controls the median for the diabetic group was 179 ng/ml compared to 188 ng/ml in the control group. Further studies have to show if there actually exists a relationship between 4-heptanone and diabetes mellitus.
Keywords: Capillary Gas Chromatography, Mass Selective Detection, Large Volume Injection, Cooled Injection System CIS, PTV, Wine Aroma
A combination of sensory testing and analysis of individual chemical species is now regarded as necessary, both for evaluation of wine character and quality as well as for a definite determination of off-flavors. In this regard advances in methodology for rapid determination of aroma compounds is an important developmental area.
In this paper a simple and fast method for enrichment and quantification of volatile compounds in wine using a solvent venting technique is described. 10 mL of wine and only 100 μL of extractant are necessary. The aroma extracts can directly be used for GC/MS analysis, without any further sample preparation.
Keywords: Direct Thermal Desorption, Air Charcoal Filters, Air Filtration, PCBs in Air, Trace Analysis, Capillary GC-MS, Cooled Injection System CIS, PTV
Many buildings constructed from prefabricated elements are widely contaminated with PCB originated in e.g. elastic sealants which act as permanent sources for several years. Indoor air filtration is part of a restoration strategy for these buildings using activated carbon filter media . The analysis of PCBs trapped on these filters is usually carried out using standard liquid extraction followed by GC/MS analysis of the extract. This standard technique will be compared to direct thermal desorption of the filter material in combination with cryo-focusing in the liner of a cooled injection system, followed by temperature programmed sample transfer to the analytical column. It will be shown that direct thermal desorption is a reliable and fast method for the determination of PCBs in air charcoal filters without requiring any sample pretreatment.
Keywords: Direct Thermal Desorption, Air Charcoal Filters, Volatile Contaminants in Air, Capillary GC-MS, Cooled Injection System CIS, PTV
The analysis of volatile organic contaminants in air trapped on an automotive air charcoal filter is usually carried out using standard liquid extraction followed by GC/MS analysis of the extract. This standard technique will be compared to direct thermal desorption of the filter material in combination with cryo-focusing in the liner of a cooled injection system, followed by temperature programmed sample transfer to the analytical column. It will be shown that direct thermal desorption is a reliable and fast method for the determination of volatiles in automotive air charcoal filters without requiring any sample pretreatment
Keywords: Breath Analysis, Thermal Desorption, Cooled Injection System CIS, GC/MS, Metabolic Disorders
The combination of a new thermal desorption module with a cooled injection system (TDS-2,CIS-3, GERSTEL) now provides a powerful thermal desorption system for direct analysis of volatile trace compounds in gaseous, liquid and solid samples. As a cooled injection system is used for the cryofocusing of the desorbed volatiles the GC/MS system still can be used for the regular analysis of liquid samples. Breath samples were collected in a 1 liter tedlar bag and transferred onto a freshly conditioned thermal desorption tube filled with Tenax. Breath analysis were performed from patients with various metabolic disorders, smoking and non smoking healthy volunteers. A MS-library was used to identify 72 components.
Keywords: Capillary Gas Chromatography, GC/MS, MultiPurpose Autosampler, Headspace, Volatiles, 4-Heptanone, 2-Ethyl-1- hexanol, DEHP, Urine, Plasma
A MultiPurpose autosampler (GERSTEL MPS), designed for liquid large volume, gaseous and headspace samples was used for the GC/MS analysis of organic volatiles in human urine and plasma. Headspace sampling with a volume, temperature and speed controlled gas tight syringe was combined with a temperature controlled cooled injection system for cold trapping, enrichment and focusing of analyte. First results from human studies under current investigations show in fact that the plasticizer DEHP is the origin of elevated 4-heptanone concentrations in urine and plasma of patients receiving intravenously applied infusions.
Keywords: Direct Thermal Desorption, GCMS, Plastizicer, Di-2-ethylhexylphthalate (DEHP), 4-Heptanone, 2-Heptanone, Cyclohexanone
The combination of a new thermal desorption module with a cooled injection system (TDS-2,CIS-3, GERSTEL) now provides a powerful thermal desorption system for direct analysis of volatile trace compounds in gaseous, liquid and solid samples. As a cooled injection system is used for the cryofocusing of the desorbed volatiles the GC/MS system still can be used for the regular analysis of liquid samples. Plasticizers can usually be analyzed by liquid extraction with alcohol/water, but special care has to be applied not to use contaminated solvents. Direct analysis of plastics by thermal desorption saves time and avoids cross contamination. Many containers for intravenous solutions are made with plasticized polyvinyl chloride, the common form of which is di-2-ethyl hexyl phthalate (DEHP). Extraction of DEHP into blood and plasma stored in such plastic containers can occur, and harmful effects of DEHP in the human body consequently have been suggested. We therefore analyzed 30 plastic tubing samples which are used for various invasive techniques in medicine.
Keywords: LC, GC, PTV, Interface
A new interface has been developed for the on-line coupling of liquid chromatography (LC) and capillary gas chromatography (GC). The interface consists of a flow cell from which a sample can be taken by the syringe of a large-volume programmed temperature vaporization (PTV) injector. The PTV injector is then operated in the solvent venting mode for injection in the capillary column. The fully automated system can be operated and the data handled by one PC. The performance is illustrated with the analysis of some phenylurea pesticides in tobacco leaves.
Keywords: Biogenic, Plant Stress, GC/MS
The novel GERSTEL Online TDS G was developed to allow fast, reliable and continuous analysis of airborne compounds. For the described application the total analysis time, including GC run time, is about 1 hour. Sampling is done in parallel with gas chromatographic analysis.
Keywords: Online LC-GC Coupling, PTV, Large Volume Injection, Alkylphenolethoxylates, Nonylphenol, Estrogenic Effect
This paper describes an online LC-GC coupling system that allows fractions from an LC eluant stream to be transferred to a standard GC system. A large volume sampler equipped with a flow-cell takes a fraction of the eluant and introduces it into a PTV using the solvent venting/stop-flow technique. Sample volumes between 10 and 1000 μL can be injected. It will be demonstrated that this system permits the determination of alkylphenolethoxylates (APEOs) and their degradation products, at ultra-trace levels in water, sludge and biological matrices.
Keywords: Large Volume Injection, PTV, Distilled Spirits, Water Removal, Solvent Venting
It is the purpose of this paper to demonstrate how injection volumes up to 50 μl of distilled spirits can be automatically and routinely injected with PTV matrix removal and subsequent splitless transfer of compounds of interest. Injection volumes can be suited to the detection limits required for different classes of compounds. In addition to complete instrumental automation an on-line software calculator for optimum venting of solvents of interest is available.
Keywords: Beverage, Food & Flavor, PTV, Large Volume Injection, Headspace, Thermal Desorption
The sources of compounds that produce desired flavors and undesired off-flavors in alcoholic and non-alcoholic beverages are the raw materials used in their production and the production process itself. There are typically hundreds of compounds present in a beverage, and the concentrations of these compounds varies enormously. This means that analytical techniques not only have to be suited to these concentration levels, but they also must be able to handle the complexity of the matrix.
This note will outline some strategies for beverage analysis resulting from recent technology advances in sample introduction techniques such as large volume injection, thermal desorption, thermal extraction and large volume (dynamic) headspace. These techniques offer significant advantages in establishing improved product authenticity fingerprints and lower detection limits. They are also useful for determining production related problems, such as off-flavors deriving from packaging materials.
Keywords: Multidimensional GC, Multicolumn Switching, Backflush, Early Vapor Exit, Venting, Large Volume Injection
Multidimensional capillary gas chromatography has been used for many years to aid in the determination of trace impurities in relatively pure products, to isolate analytes from complex matrices, and to improve chromatographic resolution. Major drawbacks to these systems have been the complexity of the hardware, difficulty of use, and system instability. A new line of multidimensional systems will be presented that overcome these drawbacks by using septumless sample introduction, microprocessor controlled proportional valves and electronic mass flow controllers, valveless switching, integrated analyte cold trapping, and complete Windows™ based software control. The line consists of three systems that are designed to cover all multidimensional applications.
Keywords: LC Fraction Collection
Multidimensional capillary gas chromatography, and, in its ultimate form, comprehensive GC, result in the highest obtainable peak capacity and overall resolution. The combination of GC techniques is however restricted to the analysis of volatile (GC amenable) compounds and the separation mechanism is mostly based on volatility (boiling point separation). High molecular weight compounds or very polar compounds cannot be analyzed or will contaminate the analytical system. The potentials of multidimensional HPLC, in this respect, are much larger and very specific separations based on hydrophobicity, polarity, ion strength, molecular size or affinity can be obtained. HPLC, on the other hand, cannot offer the same peak capacity and overall resolution as GC. HPLC and GC are thus quite complementary to each other and therefore the on-line combination of the two techniques is very interesting. Recently on-line HPLC-GC equipment became commercially available. In this paper, a new automated and modular system based on a flow cell and large volume PTV injection is presented.
Keywords: Stir Bar Sorptive Extraction - SBSE, GERSTEL Twister
A new approach using stir bars coated with PDMS was recently developed. In this approach, 50-300 μL PDMS coatings are used. Consequently, the sensitivity is increased by a factor of 100 to 1000. Complete recovery is possible for solutes with k(o/w) larger than 500. Solutes with k(o/w) from 10 to 500 can also be analyzed using calibration as is done in SPME. This technique is called stir bar sorptive extraction (SBSE). PDMS coated stir bars are now commercially available(TwisterTM, GERSTEL). Magnetic stirring rods are incorporated in a glass jacket and coated with a layer of PDMS.
Keywords: Stir Bar Sorptive Extraction - SBSE, GERSTEL Twister, Environmental Analyses
For the analysis of organic compounds in aqueous environmental matrices several sample preparation methods are used. Volatile organic compounds can be analyzed using (static) headspace, purge and trap or liquid-liquid extraction. Semi-volatiles are analyzed after liquid-liquid extraction or solid phase extraction (SPE). During the past years, miniaturization has become a dominant trend in analytical chemistry. Typical examples of miniaturization in sample preparation techniques are micro liquid-liquid extraction (in-vial extraction), ambient static headspace and disk cartridge SPE. In combination with state-of-the-art analytical instrumentation, this resulted in faster analysis, higher sample throughput, lower solvent consumption, less manpower in sample preparation while maintaining or even improving sensitivity.
Keywords: Twister, Stir Bar Sorptive Extraction SBSE, 2,4,6-Trichloroanisole, Wine, Off-Flavor, Thermal Desorption, Capillary GC/MS, Ultra-Trace Analysis
2,4,6-Trichloroanisole (TCA) is well known as being the main cause for corkiness in wine. Its extremely low odor threshold usually mandates enrichment and concentration steps before it is available for precise quantitation. This paper describes the applicability of a recently developed, novel and simple approach for sorptive extraction of organic compounds from aqueous samples for the determination of 2,4,6-Trichloroanisole in wine without the necessity of any classical sample preparation. Calibration curves will show linear responses over more than three magnitudes down to 10 ng/L in full scan and below 1 ng/L in selected ion monitoring.
Keywords: Beverage, Flavor, Stir Bar Sorptive Extraction SBSE, Twister, Thermal Desorption
The analysis of flavor compounds in beverages such as coffee, tea, soft drinks and alcoholic beverages usually requires cumbersome sample preparation steps such as li quid/liquid extraction, solid phase extraction or distillation techniques, often with the drawback of organic solvent use. Headspace and purge & trap methods do not use organic solvents, but their analyte range is restricted to volatile compounds and therefore characterize compounds that contribute to the aroma/smell of a sample, not flavor/taste. The sensitivity of solid phase microextraction (SPME) is limited by the small amount of sorptive material that can be coated on the fibers. A new extraction technique, Stir Bar Sorptive Extraction (SBSE), recently described by Pat Sandra et.al., that overcomes the major problems with classical extraction techniques is applied in this paper. With this technique, a small stir bar (10-20mm length, 1.3mm OD) is coated with polydimethylsiloxane (1mm d.f.), placed directly in the sample, and stirred for about 1 hour. During this time, analytes are extracted into the PDMS phase, which acts as an immobilized liquid phase. The stir bar is removed, rinsed with distilled water, and placed into a thermal desorption unit. Due to the hydrophobic character of PDMS, a drying step is not necessary. Heating the stir bar releases the extracted compounds into a GC/MS system for subsequent analysis with very low detection limits (parts per trillion).
Keywords: Determination of Flavor and Off Flavor Compounds in Dairy Products using Stir Bar Sorptive Extraction (SBSE) and Thermal Desorption GC/MSD/PFPD
The analysis of flavor compounds in dairy products such as milk, cream, yogurt and cheese as well as their blends with several ingredients usually requires cumbersome sample preparation steps such as liquid/liquid extraction, solid phase extraction or distillation techniques, often with the drawback of organic solvent use. Headspace and purge & trap methods do not use organic solvents, but their analyte range is restricted to volatile compounds and therefore characterize compounds that contribute to the aroma/smell of a sample, not flavor/taste. In addition heating of the sample should be avoided since this would lead to reaction products which dramatically modify the flavor and taste of any dairy product. The sensitivity of solid phase microextraction (SPME) is limited by the small amount of sorptive material that can be coated on the fibers. A new extraction technique, Stir Bar Sorptive Extraction (SBSE), that overcomes the major problems with classical extraction techniques is applied in this paper. With this technique, a small stir bar is coated with polydimethylsiloxane, placed directly in the sample, and stirred for about 1 hour. During this time, analytes are extracted into the PDMS phase, which acts as an immobilized liquid phase. The stir bar is removed, rinsed with distilled water, and placed into a thermal desorption unit. Due to the hydrophobic character of PDMS, a drying step is not necessary. Heating the stir bar releases the extracted compounds into a GC/MS system for sub sequent analysis with very low detection limits (parts per trillion).
Keywords: Headspace, Solid Phase Microextraction, SPME, Thermal Desorption, Herbs, Coffee, Tea, Polyethylene ABSTRACT
The analysis of volatiles in solids is a common analytical problem. Examples include volatile aroma compounds in foods and plant materials (coffee, tea, and herbs), residual fragrances from soaps and fabric softeners on textiles, and volatiles in polymer resins, films and plastic products. Several techniques are available that allow direct analysis of the volatiles in a variety of solid matrices with little or no sample preparation. Static headspace GC (HS-GC) is probably the most commonly applied technique for analysis of volatiles in solids. Direct thermal desorption (TDS), sometimes referred to as dynamic headspace analysis, and Solid Phase Microextraction (SPME) are alternative techniques that can now be automated. The relative sensitivity of these techniques, and the strengths and limitations of each when applied to a variety of solid matrices should be considered when choosing the most appropriate approach for a new analysis. Until now a direct comparison of these techniques for a variety of samples on equivalent instrumentation has been difficult to find. Samples from the classes mentioned above were analyzed using HS-GC, SPME and TDS sample introduction into the same HP 6890 GC instrument. Column and detector conditions were maintained the same for all sample introduction methods. Generally, sensitivity of static headspace sampling was 10-50x lower than SPME sampling. Direct Thermal Extraction was found to be 50-100x higher sensitivity than SPME sampling. Besides sensitivity, advantages and limitations of the three sample introduction techniques for dealing with various sample types (low vs. high boilers, wet samples) should be considered before choosing an analytical approach.
Keywords: Thermal Desorption, Tenax TA™, Sample drying, Herbs, Peppers
The analysis of volatiles in solids is a common analytical problem. Examples include volatile aroma compounds in foods (coffee, tea, herbs), residual fragrances from soaps and fabric softeners on textiles, and volatiles in polymer resins, films and plastic products. When high sensitivity analysis is needed, many of these sample types can be analyzed by direct thermal desorption with cryotrapping before the GC column. A wide variety of sample types can contain significant levels of water. This poses significant challenges when doing direct thermal desorption and cryotrapping for analysis of volatiles, since water can accumulate and freeze in an inlet or at the head of a column. Introduction of significant levels of water into the GC column can degrade chromatographic performance and shorten column lifetime. There are several strategies that are useful to reduce the introduction of water into a GC when doing thermal desorption. These range from offline thermal extraction with trapping of volatiles on adsorbent beds to incorporating drying steps into the thermal desorption process itself. Estimating the amount of water that can be eliminated with each of these approaches is a challenge. Volatiles in solid samples containing up to 90% water were analyzed by direct thermal desorption incorporating different drying strategies. Off line thermal extraction utilizing Tenax TA™ adsorbent was the most effective approach for eliminating large amounts of water while effectively retaining low boiling analytes. Small amounts of water (tens of milligrams) can be eliminated from samples by using Tenax TA™ packed inlet liners cooled to 20-40°C. General guidelines for choosing appropriate steps for eliminating different levels of water are summarized.
Keywords: Indoor Air Pollution, Thermal Desorption, Adhesives, Floor Coverings, Emissions, Bromophenol
Carpets for office use in most cases are applied with water-based adhesives. During the last decade the complaints about odors and emission of volatile organic compounds from these fitted carpets have increased dramatically, causing a major problem for indoor air quality. In a series of investigations it has been established that in many cases the adhesives used were the primary cause of complaints. This is initially surprising, since usually solvent free water-based dispersion adhesives were used. This paper describes the analytical approach of analyzing a broad variety of volatile compounds within a wide boiling point range with thermal desorption GC/MS.
Keywords: Olive Oil, Flavor, Off-Flavor, Rancidity, Thermal Desorption
Flavor is an important quality criterion for virgin olive oils. The identification of the compounds causing the flavor or off-flavor therefore is the key for quality control. Their analysis in olive oils usually requires more or less cumbersome sample preparation like liquid/liquid extraction, solid phase extraction or distillation techniques, often with the drawback of organic solvent use. Headspace and purge & trap methods do not use organic solvents, but their analyte range is restricted to the volatiles and therefore characterizes more the compounds contributing to aroma/smell of a sample,not the flavor/taste. Direct thermal extraction of olive oil in an inert atmosphere under controlled temperature conditions can be used to easily analyze the volatile and semi-volatile compounds contributing to flavor. 10 μL of olive oil is injected into an empty glass tube and inserted into a thermal desorption unit (TDS). The TDS was ramped to 80°C with high desorption flow, allowing the analytes to be transferred into a PTV-liner and trapped at sub-ambient temperatures (-150°C), while retaining the oil-matrix in the TDS tube. After completion of sample transfer, the PTV was ramped to 280°C, releasing the extracted compounds into a GC/MS system for subsequent analysis at very high sensitivity.
Keywords: Thermal Extraction, Polyethylene, Hydrocarbons, PET, limonene, Calibration, IDEMA
Examples of optimized conditions for quantitation of residual hydrocarbons in polymeric packaging film and residual flavor components in recycled PET are shown. Techniques and equipment necessary for reliable calibration are also described.
Keywords: Twister, SBSE, Solvent Back extraction, pH Adjustment
Strategies are shown that provide additional control of the partitioning of analytes into the PDMS phase during SBSE. Parameters such as sample pH, salt content and the presence of solvents during extraction can be used to enhance the extraction efficiency of a range of analytes including polar compounds. The very high capacity of the SBSE phase allows the use of solvent back extraction prior to thermal desorption to selectively reduce the background interference from complex sample matrices.
Keywords: Twister, SBSE, Fragrance, Acetic acid, Ethanol, Glycol, Detergent, Emulsion
Analysis of samples containing polar matrix components such as water, glycols, sugars or surfactants by gas chromatography has usually required extensive cleanup such as liquid/liquid extraction, solid phase extraction or distillation.Some polar matrix components like acetic acid or ethanol are highly volatile and difficult to eliminate using traditional sample preparation techniques. Stir bar sorptive extraction using a polydimethylsiloxane (PDMS) phase on the stir bar prior to GC analysis can eliminate major interference from these polar matrix components. The PDMS selectively extracts non-polar analytes, discriminating against the polar matrix components present in the sample at even percent levels or higher. Samples that contain high levels of interfering compounds like surfactants and emulsifiers that usually form emulsions when attempting organic solvent extractions can be analyzed directly by SBSE. Examples include separation of flavor and fragrance components in balsamic vinegar and alcoholic beverages, and analysis of fragrances and other additives in consumer products like soaps and detergents. Trace additive analysis in new and used antifreeze further demonstrates the versatility of SBSE for sample preparation prior to GC analysis.
Keywords: Stir Bar Sorptive Extraction, SBSE, Beer, Hops
The elucidation of the “hoppy aroma note” in beer has always been a challenging task. The main reason without any doubt is the lack of sensitive and selective analytical methods. In the brewery industry, organoleptic panels very often identify a hoppy note in beers, but analytical evidence cannot support their observations. Two new sampling techniques, namely stir bar sorptive extraction (SBSE) and headspace sorptive extraction (HSSE) were evaluated for the enrichment of hop derived solutes in beers.
Keywords: Stir Bar Sorptive Extraction, SBSE, Beer, Wort
A new sample preparation technique - Stir Bar Sorptive Extraction (SBSE) was evaluated for the enrichment of hop-derived solutes in wort and beer. SBSE offers an effective, easy-handling and low cost opportunity for the isolation of organic solutes from aqueous matrices. A small stir bar, coated with polydimethylsiloxane is placed directly in the sample and stirred for about an hour. After sampling, the stir bar is placed in a thermal desorption unit for subsequent GC separation under mild conditions. Several hop-derived solutes can be elucidated and identified in this way. Alternatively, the stir bar can be desorbed by a liquid followed by HPLC analysis. This allows analysis of some of the thermally stable hop derived solutes. Both approaches are complementary in nature and give a quite complete profile of the hoppy flavor in beer. The SBSE approach has also been compared to the classical SPE-HPLC technique.
Keywords: Programmed Temperature Vaporizers, PTV, Split/Splitless Inlet, Septumless Sample Introduction, Oxidative Decomposition, Thermal Degradation
The benefits of using a Programmed Temperature Vaporizer (PTV) type inlets instead of hot split/splitless (S/SL) inlets for the liquid and headspace (HS) measurements of volatile compounds are shown. The use of a PTV (GERSTEL CIS 4) for Solid Phase MicroExtraction (SPME) measurements has an advantage due to the use of a septumless head (SLH) instead of a septum for sealing the inlet. The significant accumulation of septum material inside the liner by SPME injections is demonstrated. This will lead to higher chromatographic background, restrictions in the flow through the inlet and in worst case to the loss of the fiber. This problem does not appear when using septumless sample introduction systems.
Keywords: PAH, SPME, Stir Bar Sorptive Extraction, SBSE, GERSTEL Twister, Thermal desorption, GC-MS, PCB
Two extraction techniques that avoid solvent consumption and cut down the sample preparation to a minimum - Solid Phase MicroExtraction (SPME) and Stir Bar Sorptive Extraction (SBSE) – were compared on the basis of their reproducibility and sensitivity for 16 US EPA PAH compounds.
Keywords: Soil Analysis, EPA SW-846, Method 8270, Stir Bar Sorptive Extraction, SBSE, SVOC, Accelerated Solvent Extraction, ASE
The analysis of contaminated soil and sludge samples for semi-volatile organic compounds (SVOC) has traditionally been performed using gas chromatography/mass spectrometry (GC/MS) (EPA SW-846, Method 8270). This method relies on the extraction of contaminants from the samples utilizing a variety of organic and chlorinated solvents. This study shows the effective use of a Dionex Accelerated Solvent Extractor 200 (ASE) along with Stir Bar Sorptive Extraction (SBSE) with methanol replacing the undesirable chlorinated solvents.
Keywords: Stir Bar Sorptive Extraction, SBSE, Twister, PAHs
In this study we describe the possibility of automation of the SBSE desorption step with direct transfer of the liquid extract to HPLC by use of the GERSTEL- MultiPurpose autosampler MPS (Twister Back-Extraction). For this purpose the MPS was equipped with a temperature programmable agitator and a special software. Using this procedure, after extraction of water samples by SBSE, the only manual step is the removal of stir bars from the sample vial and transfer to 250 μL glass inserts placed inside 2 mL autosampler vials. The MPS then adds the ACN/water mixture to the stir bar, transports the vial to the agitator, where it is agitated at a defined temperature during the preset desorption time and finally withdraws an aliquot of the extract, which is injected into the HPLC.
Keywords: Food packaging, Food simulants, Stir Bar Sorptive Extraction. SBSE
The FDA requires that any food-contact materials that may reasonably be expected to migrate into food must conform to existing regulations or be included in a petition proposing a new regulation. Alternatively, a no-migration status can be established by showing the packaging component is not detectable in food with a method with a LOD typically in the 1-50 ppb range. Since determination of trace component migration into complex food matrices is extremely difficult if not impossible, the FDA has established acceptable food simulating solvents to use for migration testing. These solvents (water, 3% acetic acid, 10% ethanol and 95% ethanol) comprise much simpler matrices and minimize the potential for interference. Simpler matrix notwithstanding, developing reliable analytical methods for low ppb LOD can be a formidable challenge. Stir Bar Sorptive Extraction (SBSE) followed by thermal desorption GC has been shown to provide excellent detection limits for non-polar analytes in the low ppb - ppt range. Polar matrix components such as ethanol and acetic acid do not partition into the PDMS phase on the stir bar, minimizing potential interference during analysis. This technique is therefore compatible with the FDA specified food simulating solvents. Model compounds spanning a wide polarity range were spiked into the food simulating solvents, extracted by SBSE using GERSTEL Twister stir bars, and recovered by thermal desorption GC. The presence of solvents in the sample matrix reduced analyte recovery in the stir bar, with the largest effect seen for compounds with octanol:water partition coefficients less than 500. Since partitioning into the PDMS phase is proportional to the octanol/water partition coefficient and predictable, these results provide guidelines for the types and polarities of analytes amenable to this technique.
Keywords: Stir Bar Sorptive Extraction, SBSE, SPME, Capacity
The determination of volatile and semi-volatile analytes in aqueous solutions using stir bar sorptive extraction (SBSE) as the extraction step is gaining acceptance in a wide variety of application areas including water and waste water analysis, beverages and other consumer products. In this study physical capacity of the GERSTEL Twister stir bar was determined gravimetrically by concentrating hexadecane from aqueous isopropanol solutions. Under optimal conditions, the stir bar absorbed milligram quantities of hexadecane. From a practical perspective, the highest analyte concentration that still provides a linear calibration response could be defined as the working capacity of the stir bar. For typical analytes, this upper limit was found to be in the ppm range. To assess competition and displacement effects, model compounds including a pesticide mix and methyl esters were extracted from water with Twister or SPME in the presence of up to 5 ppm limonene. Under these conditions, the most polar analytes showed the greatest reduction in peak area when extracted with SPME. Detection limits determined for model compounds showed a 10 to 25-fold advantage of the increased capacity of the Twister phase compared to SPME.
Keywords: Cryogenic air sampling, Thermal desorption, Gas chromatography, ICP/MS
A variety of volatile organometalloid species finds application in industrial processes. Among these are e.g. the fumigation of tobacco leaves or flour with phosphine (PH3) for elimination of insects, or the use of sulfurhexafluoride (SF6) as arc extinguishing media in electrical circuits. The occurrence of volatile metal(loid) species was also proved in emissions of landfills and sewage treatment plants. Most of these volatile compounds are extremely toxic even at very low concentration levels (< mg/m3), therefore a demand for trace analysis of these species exists in industrial hygiene and environmental monitoring.
Keywords: Membrane Extraction, Triazines, VOCs, Large Volume Injection, LVI
Typically membrane-assisted solvent extraction (MASE) is carried out off-line in a vial, from which the organic extract is transferred to a sample vial followed by large-volume injection (LVI). In this study the extraction device for the membrane-assisted solvent extraction was modified for use with a conventional 20 mL headspace vial. For this purpose a tube of nonporous polypropylene membrane was sealed at one end to produce a membrane pouch, which could be inserted into the vial with the aid of a stainless steel adapter. 15 mL of the aqueous sample and 500 μL of solvent was used for the extraction procedure. A GERSTEL MultiPurpose autosampler (MPS) was used to place the solvent in the membrane pouch, followed by extraction in a heated agitator. After extraction, the MPS performed LVI directly from the extraction vial.
Keywords: Stir Bar Sorptive Extraction, SBE, of Organic Acids, Amines
The determination of volatile and semi-volatile compounds in aqueous solutions using Stir Bar Sorptive Extraction (SBSE) as the extraction step is gaining acceptance in a wide variety of application areas including water, beverages, consumer products and environmental. It has been shown to be simple, sensitive, quantitative, and can often eliminate cumbersome solvent extraction or other sample preparation steps. Efficiency of partitioning into the polydimethylsiloxane (PDMS) phase on the stir bar can be predicted based on the known analyte partitioning between octanol and water as described by the octanol-water partition coefficient Kow. This prediction usually works well for most compounds, but can overestimate recovery of ionizable compounds like organic acids and amines since only the neutral form can be extracted into the bar. SBSE of organic acids and amines is evaluated from simple aqueous solutions as well as at pH extremes. Extraction behavior as a function of pH is correlated to published compound dissociation constants. Strategies to enhance extraction efficiency of ionizable compounds are discussed.
Keywords: Flavors, GC/MS, Retention Time Locking, SPME, SBSE
Analysis of foods, flavors and fragrances is commonly done by capillary gas chromatography coupled to a range of detectors depending on the particular needs of the analysis. Using Retention Time Locked (RTL) methods can facilitate the transfer from one instrument to another, particularly if different detectors (eg. MSD and FID) are used. Although liquid or headspace injection methods are often used for these analyses, difficult and time-consuming sample preparation steps, or lack of sensitivity are commonly encountered. Automated Solid Phase Microextraction (SPME) or Stir Bar Sorptive Extraction (SBSE) can often provide substantial improvements to existing methods. In this contribution, we illustrate the use of RTL methods and the Agilent RTL Flavor Library when the GERSTEL MPS 2 autosampler is used to automate either SPME or SBSE as sample extraction and introduction technique. Procedures are given for calibrating the GC method using either technique. RTL methods created for both sample introduction techniques could be moved from a GC/FID to a GC-MSD system with different column head pressure requirements. Calibrated RTL SPME or SBSE methods were then used to analyze several sample types that otherwise would pose significant matrix interference or detection limit issues. Example chromatograms with identifications based on the RTL flavor library are given.
Keywords: Membrane Extraction, Waste Water
A procedure to analyze several semi-polar, nitrogen-containing compounds in untreated industrial waste water by means of membrane extraction is described. The selected analytes cover a broad range of volatility and can be extracted with either chlororform or diisopropyl ether. Recoveries are 40 – 110% for test solutions containing approximately 250 μg/L.
Keywords: Multi-residue Method, Pesticides, Vegetables, Fruits, Green Tea, Stir Bar Sorptive Extraction, SBSE, GC/MS
A multi-residue method to determine five groups of 85 pesticides - chlorinated, carbamate, phosphorous, pyrethroid and others - in vegetables, fruits and green tea has been developed using stir bar sorptive extraction (SBSE) coupled to thermal desorption and retention time locked (RTL) GC-MS. Pre-extraction with methanol and dilution with water prior to SBSE (60 min) were performed. Dilution of methanol extract for SBSE was examined to obtain high sensitivity and to compensate the effect of adsorption to the glass wall of extraction vessel and to sample matrix for the compounds with high log Ko/w values (e.g. pyrethroid). The methanol extracts were diluted twofold and fivefold, and were simultaneously SBSE enriched. The two stir bars were placed in a single glass thermal desorption liner and were simultaneously desorbed. The versatility of the method was exhibited by its good linearity (4-100 μg/kg, r2 >0.9900) for 66 pesticides and limit of detection (LOD: < 5 μg/kg) for most of the analytes. The method enables to determine pesticides at low μg/kg in tomato, cucumber, green soybeans, spinach, grape and green tea.
Keywords: Multidimensional GC, Polymer, Headspace, Malodors
Analysts often encounter complex real-world sample types such as petroleum fractions or volatile polymer components. Resolving all individual compounds using a single chromatographic separation can be quite challenging. Coupling columns with different polarities (multidimensional GC) can significantly improve the resolution of complex samples. We coupled two low thermal mass (LTM) GC column modules with dissimilar column phases using a valveless, software controlled column switching device to perform heartcutting 2D GC on polymer headspace samples. Headspace sampling with Twister stir bars was used to introduce sufficient analyte mass on column to identify odor causing compounds. The LTM GC uses resistive heating rather than a convection oven, allowing for rapid heating and cooling rates. Column modules can be independently programmed to achieve optimal separation and short analysis times on a single GC.
Keywords: Thermal Desorption, High Boiling Compounds, GC
Thermal desorption is a valuable and versatile GC sample introduction technique for a wide variety of solid, liquid, and gaseous samples that are not amenable to direct injection into the GC instrument. Quantitative transfer of high boiling, high molecular weight compounds is quite challenging for some thermal desorption instruments that incorporate long transfer lines, valves, and various cold spots; such instruments typically fail for high-boiling compounds corresponding to C26 and higher. The GERSTEL Thermal Desorption System (TDS) is a direct-transfer thermal desorption instrument with no valves or septa seals in the flow path, and a very short, highly inert transfer line. This study tested the performance of the GERSTEL system for the determination of high boiling compounds and showed that peak areas for C15- C40 hydrocarbons were similar whether introduced to the GC/MS by liquid injection or by thermal desorption.
Keywords: Stir Bar Sorptive Extraction, SBSE, Biological Matrices, Amphetamine
Stir bar sorptive extraction (SBSE) is a novel sample preparation technique that can be used for the enrichment of solutes from biological matrices. The principle and operation of SBSE for enrichment of pharmaceutical drugs and its derivatives – phenylalkylamines and amphetamines included into the list of pharmaceutical drugs, psychotropic compounds and its precursors, subjects to control in Russia.
Keywords: Blood Alcohol, Headspace Analysis, Ethanol
Forensic laboratories face the need to analyze many samples of human blood and body fluids for alcohol content. The large number of samples that require quantification of ethanol in these facilities creates a challenge for the methodology employed. Factors that need to be considered are sample throughput, resolution, and carryover. A successful method for these analyses should be fast, precise, and accurate. Current methods used in these analyses use a gas chromatograph coupled to a static headspace sampler and flame ionization detector (FID). The x, y, z robotic autosampler used in this study has a capacity of up to 128 headspace samples, which is a distinct advantage compared to other samplers commercially available. Results obtained with the instrument and methodology described in this report meet the specifications set by the California Department of Justice Blood Alcohol Operating Procedures (Title 17). A dual-column, dual-FID blood alcohol analysis system that can be used for confirmation of ethanol peaks was also tested and produced results with good precision (below 5 % RSD).
Keywords: Multidimensional GC, Flavor, Fragrance, Polymer
Coupling columns having different polarities can significantly enhance the resolution of complex samples. This approach is commonly known as multidimensional gas chromatography. In this study, we coupled two low thermal mass (LTM) GC column modules with dissimilar column phases using a valveless, software-controlled column switching device for heartcutting GC-GC.The LTM has a resistive heating system rather than a convection oven which allows for rapid heating and cooling rates. In addition, the column modules can be independently programmed for optimal separation and minimum analysis time. This system was used to identify trace components responsible for off-odors in headspace samples from polymers by coupling an olfactometry detector to the powerful heartcutting technique. Two main advantages of the instrumental configuration used were the simple, robust design and short analysis times.
Keywords: Stir Bar Sorptive Extraction, SBSE, Multi-residue Method, Pesticides, Vegetables, Fruits, Green Tea, GC/MS
A multi-residue method for determination of five groups of 85 pesticides - organochlorine, carbamate, organophosphorous, pyrethroid and others - in non-fatty food, e.g. vegetables, fruits and green tea is described. The method is based on stir bar sorptive extraction (SBSE) coupled to thermal desorption (TD) and retention time locked (RTL) GC/MS in scan mode. The method was applied to the determination of pesticides at low μg/kg levels in tomato, cucumber, green soybeans, spinach, grapes and green tea.
Keywords: Sample Preparation, Water, Stir Bar Sorptive Extraction, SBSE, Thermal Desorption, GC/MS
This paper applies SBSE coupled to thermal desorption (TD)-GC/MS to determine ultra-trace levels (sub-ng/L to ng/L) of compounds in aqueous samples.
Keywords: Stir Bar Sorptive Extraction, SBSE, THC, GC/MS
This study demonstrates the feasibility of extracting THC from an aqueous matrix using Stir Bar Sorptive Extraction (SBSE) followed by thermal desorption into the injection port of a standard single quadrupole electron impact GC/MS to achieve detection limits less than 1.0 ng/mL. The specimen is diluted with water + methanol and extracted with a stir bar coated with a non-polar polydimethylsiloxane phase.
Keywords: Environmental Analysis, Gas Chromatography, Pesticides, PCBs
Low Thermal Mass (LTM) technology involves combining any length standard capillary GC column, a Resistance Temperature Detector (RTD) based thermal measurement system, and a precision controlled heating element in a bundle over the full length of a column. This technology enables fast heating (up to 1800°C per minute), fast cooling (350°C to 35°C in 2 minutes or less), as well as independent temperature control of up to 4 column modules on one GC platform. A mixture of C5 through C44 n-alkanes can be separated in less than 4 minutes. The combination of fast GC capability and independent temperature control of multiple column modules on one GC enables efficient dual column separation. For AN/2006/01 - 2 example, the separation of 20 standard pesticides can be accomplished in about 3 minutes. This note will review the LTM technology and present data to demonstrate the increased speed of analysis.
Keywords: Low Thermal Mass, Fast GC, Environmental, GC/MS
Routine analytical methods employing mass spectral analysis on a gas chromatograph are often plagued with long run times in order to achieve acceptable separations. Low Thermal Mass (LTM) technology, enables very fast temperature ramping and cooling, resulting in short cycle times and high sample throughput. Excellent linearity and precision in the analytical data is maintained, all performance gains are accomplished using conventional capillary columns, existing methods can be directly transferred and accelerated.The LTM system is designed to allow two GC columns to be heated independently on the same GC, thus enabling independent optimization of temperature ramps for standard dual column confirmation applications. Furthermore, the system provides the flexibility needed to separate complex samples using inexpensive and efficient 2D heart cutting with different column phases on the one GC, as well as running two relative short columns, with different phases, independently heated in series to possibly allow very complicated chromatography to be run much faster. Specific data will is presented illustrating performance when accelerating various environmental methods.
Keywords: Microvial, QuEChERS, Pesticide Residue, Motor Oil, Thermal Desorption, GRO, GC/MS
In this study we describe direct liquid injection techniques compatible with “dirty” samples containing non-volatile components. Using a glass liner that can be removed and replaced after the injection can eliminate interference from accumulated sample matrix components. Liners are designed to accommodate larger than normal liquid injection volumes to provide improved detection limits. Furthermore, the entire process including the liner exchange can be automated. To illustrate the utility of the technique, challenging liquid sample types such as samples prepared by the QuEChERS method for pesticide analysis and contaminated motor oils were repeatedly introduced into the GC. Chromatographic performance using the new sample introduction technique is compared to conventional injections into a hot inlet.
Keywords: Stir Bar Sorptive Extraction, SBSE, Restricted Access Material, Direct Extraction, Drugs, Metabolites, Biological Fluids
An experimental bio-compatible stir bar sorptive extraction (SBSE) device was prepared using a restricted access material (RAM) as the SBSE coating. The bio-compatible SBSE approach was advantageous in terms of simplifying the sample preparation procedure. The RAM-SBSE bar was able to simultaneously fractionate the protein component from a biological sample, while directly extracting caffeine and its metabolites; overcoming the present disadvantages of direct sampling in biological matrices by SBSE, such as fouling of the extraction coating by proteins.
Analytical Figures of Merit for Caffeine Determination in Plasma:
The RAM-SBSE device was simple to use, robust and re-useable with over 50 direct extractions of caffeine and its metabolites in biological fluids without significant signal loss.
Keywords: Ultra Fast GC, Environmental, Hydrocarbon Oil Index, HOI, ISO 9377-2, Low Thermal Mass Heating
Ultra-fast gas chromatographic methods for determination of the hydrocarbon oil index according to ISO 9377-2 were developed using a low thermal mass column heater (LTM). The column heater consists of a module that enables very fast and controlled heating of the capillary column. The speed of analysis for the hydrocarbon group eluting between C10 and C40 could in this way be increased by up to a factor 18 compared to the conventional method. Since the column can also be cooled very quickly, the total cycle time can be reduced to less than 2 minutes. In addition to ultra-fast screening and a fully compliant method, an analytical method was developed that allows the separation of groups of hydrocarbons eluting between n-C10 and n-C20, n-C20 and n-C30, and n-C30 and n-C40, respectively. The cycle time for this analysis was 4.5 min. The quantitative performance of chromatographic analysis, with respect to linearity and sensitivity, is comparable to the conventional method.
Keywords: SPE, Chloramphenicol, LC/MS, Automation
Solid Phase Extraction (SPE) using standard cartridges is widely regarded as the method of choice to extract analytes from samples with complex matrices or to extract and concentrate analytes from a wide variety of samples in general. In this paper, an automated SPE system is presented that is based on standard cartridges. It is shown that SPE with standard cartridges is easily and efficiently automated for use in LC/MS based determination of illegal antibiotics in food products of animal origin. An established manual SPE method was easily transferred to the GERSTEL MultiPurpose autosampler (MPS) using the SPE option under MAESTRO software control. Recovery and precision was improved while significantly reducing the time and effort required for sample preparation.
Keywords: Gas Chromatography, GC, MS, Fast GC Analysis, Low Thermal Mass Heater, LTM, Headspace, Solid Phase Microextraction, SPME
A fast HS-SPME-GC/MSD method for the analysis of flavor compounds of apples was developed. A complete profile was obtained after solid phase micro-extraction within 3 minutes GC run-time using a low thermal mass heater (LTM). Detection with a state-of-the-art quadrupole MSD allowed a data acquisition rate of 20 Hz, while the mass spectral data quality was maintained. The gain in analysis speed was approximately a factor 10 in comparison to the standard method used in the customers laboratory.
Keywords: Target GC/MS Analysis, Low Thermal Mass, LTM, Interactive Deconvolution Software
In diverse fields ranging from environmental samples to complex flavor preparations, high performance, high resolution capillary gas chromatography/mass spectrometry, GC-MS, has become the preferred technique for identifying and quantifying target compounds at trace levels. Many of these samples are characterized by very complex matrices, which provide a substantial challenge for contemporary capillary GC-MS. This situation is now even more complicated by the current trend towards faster GC analysis using reduced diameter columns, accelerated column heating, or a combination of both. In complex mixture analysis, new approaches and techniques are needed in order to extract the required data from the total ion current chromatogram. In this presentation, interactive mass spectrometry deconvolution software (IST for GC-MS) is used to determine the presence of trace pesticide levels in a complex essential oil.
Keywords: Beer, Off-flavors, Stir Bar Sorptive Extraction, SBSE, Headspace Sorptive Extraction, Twister®, GC-TOFMS
Various techniques employing polydimethylsiloxane (PDMS) as an extraction medium prior to GC-TOFMS analysis were investigated to measure off-flavors in aged beer. The techniques included stir bar sorptive extraction (SBSE), headspace sorptive extraction (HSSE), purge-and-trap (P&T) and closed-loop-stripping (CLS). SBSE appeared to provide the most accurate quantitation and was capable of detecting the most odor-active compounds. The peak deconvolution capability of the Leco Pegasus TOFMS was found critical to the detection and accurate quantitation of key off-flavor chemicals. Compared to fresh control beer, increases in furfural, furfuryl ethyl ether, furyl hydroxymethyl ketone, 2,4-dodecadienal, (E,E), benzeneacetic acid ethyl ester, ß-damascenone and 3-pyridinecarboxylic acid ethyl ester (a.k.a. nicotinic acid ethyl ester) were observed in beer samples incubated 12 wks at 30°C and increases in dimethyl disulfide, dimethyltrisulfide and benzeneacetaldehyde occurred in beer exposed to sunlight for 8 hrs.
Keywords: Stir Bar Sorptive Extraction, SBSE, Basic Drugs, Forensic Analysis
Stir bar sorptive extraction (SBSE) is an innovative sample extraction technique that can be used to process blood, urine, and tissue samples for routine drug screening in the forensic toxicology laboratory. Case specimens containing drugs typically encountered in forensic samples were evaluated using SBSE and compared with a liquid/liquid extraction method followed by GC/MS analysis. This evaluation demonstrated that SBSE method worked equally as well as the routine extraction method for the detection of basic drugs in screening forensic samples.
Keywords: Dual Stir Bar Sorptive Extraction (Dual SBSE), Thermal Desorption, Fast GC/MS, Low Thermal Mass Column Heater, LTM, Pesticide Multiresidues, Aqueous Samples
A method for fast screening of pesticide multi-residues in aqueous samples using dual stir bar sorptive extraction (dual SBSE) - thermal desorption (TD) - fast GC/MS has been developed. Recovery of 82 pesticides – organochlorine, carbamate, organophosphorous, pyrethroid and others – for the SBSE. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection:< 10 ng/L) for most of the target pesticides. The method was applied to the determination of pesticides at ng/L levels in river water and brewed green tea.
Keywords: Dynamic Headspace, Gas Chromatography, Thermal Desorption
Static (equilibrium) headspace injection is commonly used for GC determination of volatiles in solid and liquid samples. Since this technique relies on the analyte partitioning between the sample and headspace, and uses a fixed injection volume, it may not provide adequate detection limits, particularly for higher molecular weight, higher boiling analytes. In this study, we describe a new automated dynamic headspace analyzer that uses a two-needle design to flush the headspace of vessels ranging from 10 mL to 1.0 L onto replaceable adsorbent traps. The clean adsorbent traps are stored in a sealed tray on the x-y-z robotic sampler which transports them to the sample vessel, then directly to the integrated thermal desorber. This design enables automated optimization of trapping conditions including choice of adsorbent. Performance of the new system was assessed using standard sample types and compared to traditional static headspace (HS) analysis and optimized SPME sampling. In general, better detection limits were obtained with dynamic headspace while maintaining reproducibility comparable to the other techniques. To illustrate the new design, several sample types were tested with a series of adsorbent traps to choose optimal trapping conditions. A prototype DHS design was constructed for larger vessels. It was used to contain large and bulky samples for dynamic headspace analysis.
Keywords: Malachite Green, Solid Phase Extraction, LC/MS, Fish
Malachite green (MG) is a triphenyl methane dye that is highly efficient in battling fungi, bacteria and various single cell parasites. MG is traditionally used in aquaculture to treat and prevent fungal infections. MG, which is structurally related to known carcinogenic triphenylmethane dyes, is metabolized to leucomalachite green (LMG) and deposited in the fatty tissue of the fish. MG is under suspicion of being a human carcinogen and for causing damage to the human genetic material. Consumption of fish that is contaminated with MG is assumed to pose a significant health risk to humans. In 2003 the European Commission set the MRPL (minimum required performance limit) for MG and LMG to 2 μg/kg. Even though malachite green is banned as a veterinary pharmaceutical for animals used for human consumption, the authorities regularly find residues of this toxic compound or its metabolites during routine checks of fish farms. The work presented in this application note describes the configuration of a combined fully automated Solid Phase Extraction (SPE) system coupled with LC/Ion Trap MS. Method parameters are shown that provide improved detection limits for the two compounds coupled with automated sample preparation for highest laboratory productivity.
Keywords: Aflatoxins, Solid Phase Extraction, SPE, LC/MS
Aflatoxins are metabolites from molds such as aspergillus flavus and aspergillus parasiticus. Aflatoxins are classified as mycotoxins, they are among the most potent human carcinogens, found mainly in foods and feed of plant origin. High concentrations of aflatoxins have been found, for example, in pistachios, figs and cereals and aflatoxins have also been found in dairy products. Due to the high toxicity of aflatoxins, EU legislation specifies very low acceptable daily intakes and maximum residue limits (0.05-15 μg/kg). Of 17 known aflatoxins, four are mainly relevant: Aflatoxin B1, Aflatoxin B2, Aflatoxin G1 & Aflatoxin G2. This application note describes the configuration and operation of an LC/MS system combined with automated solid phase extraction and analyte derivatization for determination of the four aflatoxins listed above. Using the combined system, lower detection limits and improved chromatographic separation were achieved.
Keywords: Atmospheric nanoparticles, Thermal Extraction, TE, Comprehensive two-dimensional gas chromatography (GC x GC), High resolution time-of-flight mass spectrometry, HRTOF-MS
A method for characterization of airborne particles including the nanoparticles fraction with a diameter of 29-58 nm in roadside atmosphere is described. The method consists of thermal extraction (TE) and comprehensive two-dimensional gas chromatography (GC x GC) with novel detection capabilities, including high resolution time-of-flight mass spectrometry (HRTOF-MS), and simultaneous selective and mass spectrometric detection with a nitrogen phosphorous detector (NPD) and a quadrupole mass spectrometer (qMS).
Keywords: Drugs, Urine, Blood, Dean‘s Switch, Multidimensional GC, Low Thermal Mass, LTM, Fast GC/MS
Reduction in analysis time is an important goal for easing the burden of large sample sets associated with routine screening of blood samples and sample sets produced from drug metabolism studies. This study focuses on reduction in analysis time for simultaneous detection of delta-9-THC, 11-OH-THC, and THC-COOH in whole blood and urine extracts. This was achieved using the GERSTEL fast GC system combined with an Agilent GC-MSD. Addition of the fast GC system allows three independently heated temperature zones for multidimensional chromatography using Agilent Capillary Flow Technology Dean’s Switches along with fast heating/cooling rates. A novel pre-column approach protects the analytical columns in independent temperature zones and adds a high level of robustness. The Agilent Capillary Flow Technology Dean’s Switch allows a combination of heartcutting multidimensional GC and back flushing to reduce the amount of unwanted background components. Standard analysis time was reduced from 15 minutes to less than 11 minutes for blood samples and from 15 to less than 8 minutes for urine samples. Two Agilent Capillary Flow Technology Deans Switches in tandem were used for this analysis. Three independently programmed pressure zones were used in conjunction with three independent heated zones. The MS was operated in the EI mode.
Keywords: DPX, SPE, Pesticides, Fruits, Vegetables
Disposable Pipette Extraction (DPX) has been shown to be a rapid, efficient and reproducible method for performing solid-phase extraction (SPE) of pesticides from fruits and vegetables. DPX is a unique SPE method because the solid phase sorbent is contained inside a disposable pipette tip and is mixed with sample solutions. This mixing allows for the use of less solid phase sorbent material and results in faster extractions. Elution can be performed using small amounts of solvent, effectively providing a concentration step. Hence, solvent evaporation is not required for many applications such as pesticide analyses. Without the need for centrifugation or solvent evaporation, DPX methods can be readily automated and the resultant eluents directly injected into a gas or liquid chromatograph. The analyst is only required to initially process the samples to be analyzed and place the sample solutions into corresponding vials. The rest of the sample preparation can be automated, including the injection of the eluent into the analytical instrument. In this study, samples of fruits and vegetables (spiked with various pesticides) are blended with organic solvent, and the samples are then filtered and placed into sample vials. A GERSTEL MultiPurpose autosampler (MPS) is used to perform the DPX extractions and inject into the chromatographic instrument. Various types of fruits and vegetables are included in this study, and numerous pesticides are analyzed by this method including organophosphates, organochlorines, pyrethroids, and fungicides.
Keywords: Aldehydes, Ketones, Food, Fish, Dynamic Headspace
In this paper we report on the use of a novel dynamic headspace system (DHS) to determine several aldehydes, ketones and other fatty acid degradation markers in oily samples. Samples were kept in standard 20 mL screw cap vials. During dynamic headspace sampling inert gas (nitrogen) was purged through the headspace of the vial. Analytes were purged from vial and concentrated on adsorbent packed tubes placed in the gas exit. Adsorbent tubes can be filled individually and are exchangeable, making it possible to use a new tube for every sample. After sampling a defined volume, the tubes were transferred to a thermal desorption system where they were desorbed, transferring the analytes to the GC/MS system. The entire process was automated using an industry standard GERSTEL MultiPurpose autosampler (MPS).
Keywords: Dynamic Headspace, Gas Chromatography, Replaceable Traps
Static (equilibrium) headspace sampling is commonly used for GC determination of volatiles in solid and liquid samples. Since this technique relies on the analyte partitioning between the sample and headspace and uses a fixed injection volume it may not provide adequate detection limits, particularly for higher molecular weight, higher boiling analytes, and for polar analytes in aqueous samples. In this study we describe the use of an automated dynamic headspace sampler for determination of volatiles in high water content solids and aqueous samples. This sampler uses a two-needle design to flush the headspace of standard headspace vials onto replaceable adsorbent traps that can be thermostatted to control interference from water vapor. After sample collection, the adsorbent traps can be automatically dry purged to further eliminate trace water before introduction into the integrated thermal desorber. This design enables automated optimization of trapping conditions including choice of adsorbent, and has the potential for automated internal standard addition and automated calibration. Performance of the new system was compared to traditional static headspace analysis using high water content solid samples like fruits and vegetables, and also beverages. To illustrate the versatility of the new design, several sample types with high water content were tested with a series of adsorbent traps to determine optimal trapping conditions. Better detection limits were obtained with dynamic headspace for all sample types.
Keywords: Automation, Sample Preparation, Filtration, Weighing, SPE, Saponification, Esterification
A robotic X-Y-Z coordinate autosampler commonly used for sample introduction in GC or HPLC can be used to perform a wide variety of sample preparation techniques using a single instrument and controlling software. The MAESTRO software enables control of an expanded list of sample preparation techniques such as derivatization, addition of an internal standard, saponification, esterification, analytical weighing, filtration, and solid phase extraction. In addition to ease of use and intuitive windows-based setup, the software includes tools to automate and optimize timing parameters ensuring efficient sequence creation and maximum sample throughput. The sampler can be configured as part of a GC or LC system or can be configured as a benchtop workstation.
In this paper, we discuss various sample preparation techniques available when using the robotic autosampler in conjunction with the MAESTRO software. Examples of automating techniques such as solid phase extraction, Twister solvent back extraction for HPLC, and steps such as sample weighing are shown.
Keywords: Low Thermal Mass, LTM, Fast GC-ECD, SPE, PCB, Waste Oil
A fast SPE-GC-ECD method for the analysis of PCBs in waste oil was developed. A complete profile was obtained following SPE with a 12 minute GC run-time using a low thermal mass column heater (LTM). Full automation of the sample preparation and analysis (except sample weigh-in) enables a daily throughput of 100 samples. A wide range of concentrations can be determined using a dedicated column and Electron Capture Detection (ECD).
Keywords: Dynamic Headspace, Gas Chromatography, Replaceable Traps
In this study we describe the use of an automated dynamic headspace sampler for determination of volatiles in aqueous samples. This sampler uses a two-needle design to flush the headspace of standard headspace vials onto replaceable adsorbent traps that can be thermostatted to optimize analyte recovery and control interference from water vapor. Following analyte transfer, the adsorbent traps can be automatically dry purged to further eliminate water before introduction into the integrated thermal desorber. This design enables automated optimization of trapping conditions including choice of adsorbent, and has the potential for automated internal standard addition and automated calibration. To illustrate the versatility of the DHS system, examples of the determination of trace levels of volatile organic compounds (VOCs) in aqueous samples are shown. Detection limits and linearity are discussed in the following.
Keywords: Static Headspace, Multiple Headspace Extraction, MHE, Matrix Effects, Method Validation
A novel purge tool for the GERSTEL MultiPurpose autosampler (MPS) under MAESTRO software control allows the headspace of a sample vial to be purged with inert gas between injections. This new feature enables the syringe based MPS to perform MHE quantitation. The tool also allows automated purging of headspace samples prior to extraction. A brief explanation of MHE methodology along with specific examples will be given.
Keywords: Disposable Pipette Extraction, DPX, Solid Phase Extraction, SPE, Large Volume Injection, LVI, Tetrahydrocannabinol, THC, Cooled Injection System, CIS, PTV
Disposable Pipette Extraction (DPX) has been shown to be a rapid, efficient and reproducible technique for performing solid-phase extraction (SPE) of drugs from biological specimens. The combined system described in this paper provided excellent throughput for analysis of THC and metabolites. Derivatization of THC, OH-THC and COOH-THC was performed by using a mixture of BSTFA and MTBSTFA. Limits of detection were determined to be 0.5 ng/mL for THC and OH-THC and 2 ng/mL for COOH-THC. Coefficients of variation were below 5 % for all 3 analytes. Extraction efficiencies were found to depend mostly on the initial protein precipitation step. Recoveries for the DPX extraction (post precipitation) were close to 80 % for THC.
Keywords: Disposable Pipette Extraction,DPX, Solid Phase Extraction, SPE, Large Volume Injection, LVI, Sample Preparation
In this work an automated DPX procedure is presented that enables the determination of acidic, basic, and neutral drugs in small blood or urine samples. The DPX method is based on a mixed-mode cation exchange sorbent (CX) with reversed phase characteristics. The automated extraction is shown to require only minimal manual labor when performed using the GERSTEL MPS autosampler under MAESTRO software control. GC/MS data is provided showing that comprehensive, rapid and sensitive analysis can be performed using automated DPX combined with large volume injection. Automated sample preparation steps are performed during the GC/MS run of the preceding sample using the MAESTRO PrepAhead function. PrepAhead sample preparation enables high throughput analysis, improved productivity and “just in time” preparation of each sample.
Keywords: Sequential Stir Bar Sorptive Extraction, Sequential SBSE, Thermal Desorption, GC/MS, Organic Pollutants, Water Analysis
A novel stir bar sorptive extraction (SBSE) procedure - "Sequential SBSE" was developed. Compared to conventional SBSE, sequential SBSE provides more uniform enrichment over the entire polarity/volatility range for organic pollutants at ultra-trace levels in water. Sequential SBSE consists of a SBSE performed sequentially on a 5-mL sample first without modifier using one stir bar, then on the same sample after addition of 30 % NaCl using a second stir bar. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection: < 10 ng/L) for most of the model compounds even with the scan mode in the MS. The method was successfully applied to screening of pesticides at ng/L level in river water samples.
Keywords: Disposable Pipette Extraction, DPX, QuEChERS, Automation, Pesticides
One of the most important aspects of reducing pesticide exposure is monitoring of pesticide residues in foods. A number of analytical methods have been developed, many of them based on traditional liquid-liquid extraction, gelpermeation or solid phase extraction in combination with GC/MS or LC/MS. Recently, the QuEChERS (quick, easy, cheap, effective, rugged and safe) sample preparation methods have been developed to help monitor pesticides in a range of food samples. These methods, however, still require many manual steps, such as centrifugation, leading to increased total analysis time. There is a need for a simple, reliable and readily automated technique to clean up QuEChERS type extracts in order to improve laboratory productivity for monitoring pesticide residues in foods. In this study, we present a novel solid-phase extraction technique called disposable pipette extraction (DPX). The solid-phase sorbent contained in the DPX tip is loose, which permits mixing of solutions to provide unsurpassed extraction efficiency and short equilibration times. DPX extractions are automated using the GERSTEL MultiPurpose Sampler (MPS), enabling efficient, high-throughput sample preparation. The GERSTEL DPX-Q and the DPX-Qg with graphitized carbon black, represent the only commercially available automated QuEChERS application for multi-residue analysis of pesticides.
Keywords: Solid Phase Extraction, SPE, Liquid Chromatography, Sample Analysis, Lab Automation
Solid phase extraction (SPE) is one of the sample preparation methods most widely used by chromatographers, as demonstrated by the numerous published SPE methods found in the literature. Manual SPE cartridge formats can vary from disks through individual cartridges with a range of different volumes to 96-well plates. However, solid phase extraction methods can be tedious and time consuming when performed manually. There is therefore an increasing need for the automation of solid phase extraction methods. A robotic X-Y-Z coordinate autosampler commonly used for sample introduction in GC or HPLC can be used to perform a wide variety of sample preparation techniques using a single instrument and controlling software. The MAESTRO software allows the user to control the automation of solid phase extraction methods. In addition to ease of use and intuitive windows-based programming, the tools to optimize method parameters ensuring efficient sequence creation and maximum sample throughput. The sampler can be configured as part of a GC or LC system or as a benchtop workstation. In this study, we show that existing manual SPE methods can be transferred to standard format automation cartridges and automated using the robotic autosampler in conjunction with the software. Examples of solid phase extraction methods illustrating the conversion from manual to automated methods are shown.
Keywords: Sample Preparation, DPX, Opiates, Automation
The analysis of opiates in blood and urine was accomplished using automated Disposable Pipette Extraction (DPX) followed by LC/MS analysis. The automated extractions were performed in about 5 minutes using a GERSTEL MultiPurpose Sampler (MPS). The eluents were subsequently dried and reconstituted in solvent and injected into a HPLC/MS/MS instrument. Recoveries ranged from 60 to 85% for the opiates in blood, and recoveries ranged from 78 to 85% for the opiates in hydrolyzed urine. The %RSDs were lower than 6% for all analytes.
Keywords: DPX, LC/MS/MS, Sample Preparation, Lab Automation
This study focuses on the automated extraction of small sample volumes coupled to LC/MS/MS in order to provide high throughput analysis of an extended list of benzodiazepines. Using a GERSTEL MPS autosampler, DPX extractions of a variety of biological matrices were performed, using a mixed-mode cation exchange (DPX-CX) sorbent. The resulting eluents from the automated DPX extractions were then introduced into an Agilent 6410 LC/MS/MS instrument. Coupling DPX to LC/MS/MS provides rapid, just-in-time sample preparation for high throughput analysis. Data show the use of an Agilent 6410 LC/MS/MS instrument to be a highly sensitive procedure for the analysis of benzodiazepines with limits of quantitation of 0.5 ng/mL, and good linearity. The DPX extraction removes potential matrix interferences and ion suppression, and high sensitivity is therefore achieved.
Keywords: fragrance Extraction, Stability Testing, Quality Control
Accurate qualitative and quantitative analysis of perfumed or flavored products is essential to the flavor and fragrance industry. Especially when unknown samples need to be analyzed, traditional methods of GC analysis often lead to only vague results and often require time consuming and cumbersome sample preparation techniques such as solvent extraction (liquid/liquid, Soxhlet, Likens-Nickerson). The technique of dynamic headspace requires minimal sample preparation, and significantly reduces overall analysis time while also improving data quality. In this work, the dynamic headspace technique is applied to different types of consumer products. The analysis of neat perfume oil is compared with that of consumer products containing the same oil.
Keywords: Static Headspace, Residual Solvents, USP <467>
USP Residual Solvents is a general chapter in the US Pharmacopeia that describes a headspace gas chromatographic method for the determination of residual solvents in pharmaceutical products, active ingredients, and excipients. As originally written, it described parameters used with balanced-pressure or pressure loop based headspace instruments. Recent updates have included parameters for syringe based systems.
This application note demonstrates implementation of USP Residual Solvents using the GERSTEL MPS configured as automated headspace sampler. Children’s non-aspirin (acetaminophen) suspension liquid was purchased locally and spiked to a level of 2000 μg/g (5 times the acceptable concentration limit) with acetonitrile.
Keywords: Selectable 1D/2D GC/MS, SBSE, Food, Flavor, Fragrance
Identification of important trace components in complex samples like fragrances, natural products, petroleum fractions or polymers can be challenging. Achieving the mass on column and resolution necessary to locate and identify trace components using a single chromatographic separation can be difficult if not impossible. A selectable 1D/2D GC/MS configuration using Agilent capillary flow technology (CFT) and low thermal mass (LTM) GC column modules with dissimilar column phases was used to perform heartcutting 2D GC on two sample types. Stir Bar Sorptive Extraction was used as a solventless means to introduce sufficient mass of sample extract onto the pre-column of the multidimensional system. When additional mass is necessary to detect the analyte of interest in the second dimension separation, a selectable cryotrap after the pre-column can function as a fraction collector to accumulate fractions from many replicate chromatographic separations of the sample extract. Separation and identification of selected trace components from beverages and consumer products were used to demonstrate the effectiveness of this system. The main advantages of this configuration were the simple selection of one or two dimensional operation and the ability to collect multiple fractions to maximize signal from trace components in the second dimension.
Keywords: PTV Injection, Static Headspace, Dynamic Headspace, Alcoholic Beverages
Direct injection for gas chromatographic profiling of alcoholic beverages is usually preferable, but where spirits and liquors contain appreciable amounts of non-volatile material, some mode of pre-treatment may be required to avoid both inlet and column contamination. This consideration applies in particular to products aged for extended periods in wooden barrels and especially products containing added sugar, as volatile artifacts from sugar decomposition in the hot injection port can also complicate the chromatogram. In this paper a combination of static and dynamic headspace analysis is described for profiling both abundant and trace compounds in these products. Static headspace is used with a Tenax packed injection port liner for the abundant compounds. Dynamic headspace uses an additional purging step to a second Tenax liner which can then be desorbed to the same injection port liner used for the simple static headspace. In this case, the previous abundant compounds are overloaded in the chromatogram but many additional trace compounds are now apparent. For both techniques the only sample preparation required is dilution of the sample in a headspace vial and relevant automated sequences in either static or dynamic mode are also run using the same autosampler. A PTV injector in solvent vent mode is used in both cases for lowest detection limits. Application of this combined approach constitutes an effective routine analysis protocol for this particular class of products while avoiding dry extract contamination.
Keywords: Immunosuppressant, Blood Analysis, LC/MS/MS
After organ transplantation the clinical therapeutic drug monitoring (TDM) of immunosuppressant drugs in blood is an important part of the therapy to prevent organ rejection. Cyclosporine A, Everolimus, Sirolimus and Tacrolimus are the most commonly prescribed drugs for this therapy. Due to individually different pharmaco- kinetics, patients receive combinations of the immunosuppressants and the resulting drug level has to be monitored on a regular time basis. LC-MS/MS analysis methods are well established for this compound class. The most critical part of the overall application is the sample preparation step. Offline techniques are time-consuming, expensive and often inaccurate. Therefore automated sample preparation protocols, combined with LC-MS/MS, are of great interest to clinical laboratories. This work describes a new blood analyzer system, which combines automated sample tracking, sophisticated sample preparation, sensitive detection, and customized reporting for the determination of relevant immunosuppressants in a clinical environment.
Keywords: Pesticide Analysis, Matrix Effects, QuEChERS, Automated Liner Exchange, ALEX, Cooled Injection System, CIS, PTV
Fruit and vegetable extracts that are produced following the well established QuEChERS method typically contain a significant amount of nonvolatile matrix material. After several injections of such extracts into the GC, sufficient matrix residue will be present in the GC inlet liner to lower or sometimes even increase the response of certain pesticide compounds affecting the accuracy of the analysis. The performance can be restored by exchanging the GC inlet liner. Normally this has to be done manually which means stopping the analysis sequence. The GERSTEL Automated Liner Exchange system (ALEX) provides an automated solution. As this study shows, automated liner exchange restores the original performance of the GC system and is therefore generally useful for the analysis of extracts that contain nonvolatile matrix residue.
Keywords: Drugs of abuse, Pharmaceuticals, Tissue samples, Stir Bar Sorptive Extraction, SBSE, Thermal Desorption
Stir Bar Sorptive Extraction (SBSE) is an innovative and efficient method for the extraction of drugs and pharmaceuticals from blood, urine and tissue samples in a forensic toxicology laboratory. As shown in this application note and earlier publications, SBSE is an effective screening tool for drugs and pharmaceuticals in biological fluids and tissue. The SBSE technique is easy to use and the method described in this publication is performed without additional use of organic solvents, centrifugation, or the liquid transfer steps that are normally necessary when performing liquid-liquid or solid-phase extraction.
Keywords: 2-Methyl Isoborneol, Geosmin, Haloanisole, Drinking Water, Dynamic Headspace, Selectable 1D/2D, GC/MS, Olfactometry
A method for the determination of trace amounts of off-flavor compounds such as 2-methyl isoborneol (MIB), geosmin and 2,4,6-trichloroanisole (TCA) in drinking water is described based on dynamic headspace coupled to selectable one dimensional or two-dimensional gas chromatography - mass spectrometry with simultaneous olfactory detection(DHS-1D/2D-GC-O/MS).
Keywords: Thermal Desorption, Thermal Extraction, u-vial, Oil, Motor Oil, Ehthanol, Fuel, Automation, Headspace Analysis, Full Evaporation Technique
In this study, different manual sample preparation procedures and one automated sample preparation procedure were tested in two consecutive round robin tests for quantitative determination of ethanol in complex oil samples such as motor oil and blow by gas condensate.
Keywords: EG-Silicone, Twister, Stir Bar Sorptive Extraction, SBSE, Thermal Desorption, GC/MS, Whiskey, Wine, Juice
This paper describes a novel ethylene glycol (EG) and silicone based combined sorbent phase developed for stir bar sorptive extraction (SBSE) using the GERSTEL Twister™. EG-Silicone, polyacrylate (PA), and polydimethylsiloxane (PDMS) Twisters were used separately to perform SBSE on whisky, white wine and multivitamin juice in order to determine the usefulness of these phases for generating qualitative flavor profiles of beverages.
Keywords: Pyrolysis GC, Automated Pyrolysis, Thermal Desorption
This paper describes an automated pyrolysis system for gas chromatography (GC) based on a filament type pyrolyzer combined with a commercially available thermal desorption instrument, onto which the pyrolysis module is installed. Automated sample introduction for both pyrolysis and thermal desorption is performed using a commercially available autosampler. For pyrolysis of solid, liquid, or melting samples the use of different types of sample holders is investigated, for example cup-type holders for liquid samples. A special design has been developed that enables accelerated gas phase transport to help reduce the formation of secondary pyrolysis products. Sample holder design and complete fl ow path heating are essential design aspects in order to maximize recovery and minimize carry-over, enabling the system to reliably perform automated analysis of batches of different sample types. These aspect are discussed.
Keywords: Dispersive Solid Phase Extraction, Automation, QuEChERS, Pesticides
This paper describes an automated dispersive SPE (dSPE) cleanup method for QuEChERS extracts that is performed with commercially available kits from Agilent® Technologies. Extraction and clean-up is performed using a micro-scale version of this method and automation is achieved using a GERSTEL MPS autosampler equipped with an Anatune CF-100 centrifuge. The clean-up process is followed by automated injection of the cleaned extract to a GC/MS system using the GERSTEL Automated TDU-liner EXchange (ATEX) technique. The sensitivity and selectivity of GC/MS combined with the described injection technique, results in method detection limits that meet acceptance criteria for reporting maximum residue levels (MRLs) as established by regulatory agencies. The ability to automate the dSPE clean-up of QuEChERS extracts and to couple extraction and clean-up directly to GC/MS analysis, results in the improved laboratory productivity by streamlining the complete analytical process.
Keywords: DPX, LC-MS/MS, Sample Preparation, Laboratory Automation
This study focuses on the automated extraction of small sample volumes combined with LC-MS/MS analysis providing high throughput analysis of common pain management drugs. Using a GERSTEL MultiPurpose Sampler (MPS), DPX extractions of hydrolyzed urine were performed, using a reversed phase sorbent with a proprietary salt additive (DPX-RP-S). The resulting eluents from the automated DPX extractions were introduced into an Agilent 6460 LC-MS/MS instrument.
Keywords: DPX, Solid Phase Extraction, Mycotoxins, Aflatoxin B1, LC/MS/MS
The extraction of Aflatoxin B1 residues from contaminated corn samples using disposable pipette extraction (DPX) is described. DPX is a solid-phase extraction (SPE) technique that is based on loosely contained sorbent inside a pipette tip fitted with a screen. This device provides faster extraction because only minimal conditioning steps are needed. A weak anion exchange sorbent (DPX-WAX) was found to provide selective extraction of Aflatoxin B1 from a crop sample. Recovery of the analyte of interest was 81 % with a relative standard deviation of 8 %.
Keywords: Thermal Desorption, Gas Chromatography, Mass Spectrometry, Stir Bar Sorptive Extraction, SBSE, GERSTEL Twister, Pyrolysis
This study shows the analysis of a commercially available personal care product using the GERSTEL MultiPurpose autosampler (MPS) configured with Thermal Desorption Unit (TDU), Cooled Injection System (CIS) PTV-type inlet, Dynamic Headspace (DHS) and pyrolysis (PYRO) modules in combination with a GC/MS system. Information regarding product composition can be obtained from the chromatographic profiles obtained from one analysis system using a variety of sample introduction techniques.
Keywords: DPX, LC-MS/MS, Sample Preparation, High Throughput Laboratory Automation
This study focuses on the automated extraction of small volumes of urine samples (< 500 uL) using disposable pipette extraction (DPX) for the comprehensive screening for pain management drugs by LC-MS/MS. Using a GERSTEL MPS autosampler, DPX extractions of hydrolyzed urine were performed, using a reversed phase (DPX-RP-S) sorbent. The resulting eluents from the DPX extractions were automatically diluted and injected into an Agilent® Technologies LC-MS/MS system. Sample preparation was performed just-in-time enabling high throughput screenings, averaging a cycle time of 7 min/sample. Validation results show that the automated DPX-LC-MS/MS screening method provides adequate sensitivity for over 65 analytes and internal standards. Lower limits of quantitation (LLOQ) ranged between 0.5 – 50 ng/mL and % RSDs were below 10% in most cases.
Keywords: Phenols, Whiskey, Capillary GC/MS, LVI, Solvent Vent, TDU, SBSE, Deconvolution
In this study, a method was developed for quantitative determination of seven phenolic compounds in scotch whisky. Two different whisky brands were analyzed by Stir Bar Sorptive Extraction (SBSE), based on novel EG-Silicone Twisters, combined with thermal desorption gas chromatography-mass spectrometry (TD-GC-MS). Direct Large Volume Injection (LVI) GC/MS was used as reference method. Optimized methods for LVI-GC/MS and SBSE-TD-GC/MS analysis were used for quantitative determination of the target compounds: phenol, o-,m-, and p-cresol, guaiacol, 4-ethylguaiacol, and 4-ethylphenol. Both methods were evaluated regarding linearity of calibration, reproducibility, and limits of detection (LOD), or limits of quantification (LOQ), for the target compounds. These values were calculated for pure whisky (40 % v/v, ethanol/water).
Keywords: Extractables, Leachables, Food Packaging Materials, Medical Materials, Automated Sample Preparation, Liquid Injection, Thermal Desorption, Gas Chromatography
This application note describes two automated methods for screening of extractable compounds from materials for food packaging, medical or technical purposes. The first method is based on automated liquid extraction performed by the GERSTEL MultiPurpose autosampler (MPS), the second involves thermal desorption of the material in question in the GERSTEL Thermal Desorption Unit (TDU). Both methods are suitable for gaining an overview of the quality and emission potential of a material and therefore useful in the search for a suitable packaging material. The methods deliver comparable qualitative results.
Keywords: Thermal Desorption, Gas Chromatography, Mass Spectrometry, Twister, Stir Bar Sorptive Extraction, SBSE
This study shows the analysis of several commercially available coconut water products using a GC/MS system equipped with a versatile autosampler and sample preparation robot capable of performing a wide range of standard sample introduction techniques including thermal desorption. A fast and efficient analysis method based on stir bar sorptive extraction (SBSE) in combination with thermal desorption-GC/MS was developed for the determination of flavor compounds, pesticides, antioxidants, compounds migration from packaging materials, and off-flavors in coconut water
Keywords: Full Evaporation Dynamic Headspace, Fragrance, Quality Control
The ability to perform accurate qualitative and quantitative analysis of perfumes or flavored products is essential to the flavor and fragrance industry. Especially when unknown samples need to be analyzed, traditional methods of GC analysis often lead to only qualitative results and often rely on time consuming and cumbersome sample preparation techniques such as solvent extraction (liquid/liquid, Soxhlet, Likens-Nickerson). In this work, the analysis of neat perfume oil is compared with that of consumer products containing the same oil, applying different traditional analytical techniques like static headspace, SPME, SDE, and comparing the results with those of a dynamic headspace approach. It will be shown that the technique of dynamic headspace requires minimal sample preparation and significantly reduces overall analysis time while delivering improved data quality.
Keywords: Automated Evaporation, mVap, SPE, DPX
Having to reach ever lower limits of detection is a daily challange in modern laboratories. In order to succeed in obtaining sufficiently sensitive analysis methods, sample preparation techniques such as Solid Phase Extraction (SPE) or Liquid-Liquid Extraction are often used as concentration steps. The concentration factor achieved in these cases depends on the amount of solvent used for analyte elution from the SPE cartridge or for liquid extraction. Following the extraction step, further concentration of analytes can be achieved by reducing the amount of solvent left in the extract. This is typically achieved by evaporation. Such a concentration step can contribute significantly to improved limits of detection for the overall analytical method. For the evaporative concentration step, commercially available rotary evaporators as well as custom solutions are widely used. These are mainly stand-alone systems for manual operation. The GERSTEL MultiPosition Evaporation Station (mVAP) in combination with the GERSTEL MultiPurpose Sampler (MPS) now offers fully automated concentration of sample extracts. The system enables complete automation of all sample preparation steps including introduction to an a LC or GC system. The evaporation is controlled by controlling the applied vacuum leading to reproducible results independent of the solvent used. The user can also benefit from a real increase in laboratory efficiency, since batches of samples can be processed automatically overnight. In this Application Note we demonstrate the performance of the mVAP and compare the results with those obtained using a commercially available evaporation system based on nitrogen flow.
Keywords: DPX, LC/MS/MS, Sample Preparation, High Throughput Laboratory Automation
This study focuses on the rapid cleanup of urine samples (< 500 uL) using disposable pipette extraction (DPX) for high throughput LC/MS/MS screening of buprenorphine (Bup) and main active metabolite norbuprenorphine (Nbup). Using a GERSTEL MultiPurpose autosampler (MPS), DPX extractions of hydrolyzed urine were performed, and analysis results were directly compared to results obtained using the "dilute-and-shoot" (D&S) approach for the same samples. The automated DPX cleanup process significantly reduced matrix effects without compromising the required minimum reportable limits (MRLs), whereas when using the D&S approach, samples had to be diluted by up to a factor 100 to remove such effects, which directly affected the ability to determine Bup and Nbup at the MRLs. Moreover, the addition of valve switching control from MAESTRO software further increased the throughput potential of the solution. The resulting eluents from the automated DPX extractions were injected into an Agilent 6460 LC/MS/MS instrument configured with 2 LC pumps (gradient and re-generative) allowing rapid, just-in-time sample preparation for high throughput screening, averaging a cycle time of 4 min/sample.
Keywords: Selectable 1D/2D GC/MS, SPME, Food, Flavor, Fragrance
Identification of important trace components in complex samples like fragrances, natural products, polymers or food products can be challenging. Achieving the mass on column and resolution necessary to locate peaks and identify trace components using a single column chromatographic separation can be difficult, if not impossible. A selectable 1D/2D GC/MS configuration based on Agilent® Technologies capillary flow technology (CFT) and low thermal mass (LTM) GC column modules with dissimilar column phases was used to perform two-dimensional GC analysis of different foodstuffs. Heartcutting was used to transfer analytes from the first to the second column. Mass spectrometry and olfactory detection were performed in parallel. Solid Phase Microextraction was used as a solventless means to introduce sufficient mass of sample onto the pre-column of the multidimensional system. SPME offers the added benefit of enabling "tuning" of the selectivity of the extraction through the choice of coating on the fiber. Separation and identification of selected flavor compounds from food products were used to demonstrate the effectiveness of the system. The main advantages of this configuration were the simple selection of one or two dimensional operation in combination with the ability to use mass spectrometry and olfactory detection in both dimensions for the analysis of odor active compounds.
Keywords: Ethyl Carbamate, Distilled Spirits, Capillary GC/MS, LVI, Solvent Vent, multidimensional column switching
A procedure is presented for quantification of ethyl carbamate at low ug/L levels in distilled spirits. A 100 uL large volume injection was used followed by orthogonal 2-dimensional GC/MS with heartcutting. The direct large volume injection ensured sufficient availability of analyte without an initial sample preparation step, and the 2D step allowed clean elution of ethyl carbamate and it’s labelled internal standard and compensated for the difficult detection of low mass non-specific ions in a complex matrix. The 2D separation was achieved using the new GERSTEL uFlow Manager based on metal ferrules for simple connection of the orthogonal columns. The principle and apparatus required for both large volume injection and 2D separation will be described together with results from actual samples.
Keywords: Doping, Equine Urine, Automated Sample Preparation, Disposable Pipette Extraction, Triple Quadrapole Mass Spectrometry, Gas Chromatography
This application note describes a fully automated method for the determination of selected doping compounds in equine urine. A GERSTEL MultiPurpose autosampler (MPS) with Disposable Pipette Extraction (DPX) option is employed for extraction and cleanup. After gas chromatographic separation the analytes are detected by a triple-quadrupole mass spectrometer (QqQ-MS). The method is rugged, provides an excellent cleanup of the complex sample matrix and shows very good limits of detection, from below 0.1 to just under 10 ng/mL, when compared to labor intensive manual manual SPE methods.
Keywords: Stri Bar Sorptive Extraction, SBSE,GC/MS, Phenols, Off-flavor, Water
16 phenolic compounds along with typical drinking water off-flavor compounds like geosmin, 2-methylisoborneol(MIB), and 2,4,6-trichloroanisole (TCA) were determined using two different approaches: 1) In-situ derivatization with acetic anhydride followed by SBSE using the PDMS Twister and Thermal Desorption (TD)-GC/MS; 2) Direct SBSE without derivatization using the EG-Silicone Twister and subsequent TD-GC/MS. In the case of the EG-Silicone twister, derivatization is not required due to its higher affinity for polar compounds. Both methods were evaluated for the extraction of 0.01 to 1 μg/L of phenols from water samples.
Keywords: Solid Phase Extraction, SPE, LC/MS/MS, Sample Analysis, Laboratory Automation
Acrylamide is thought to be produced during the roasting process associated with coffee production. Acrylamide has been labeled as a probable human carcinogen. Due to the use of roasted coffee beans in making coffee and the high consumption of coffee world-wide, brewed coffee could be a source of daily exposure to acrylamide. Acrylamide determination has been shown to be challenging due to presence of co-extractives in the final extract. Manual solid phase extraction followed by LC-MS/MS analysis has been reported as a successful method for the determination of acrylamide from brewed coffee samples. However, performing solid phase extraction manually can be tedious and time consuming and there is increasing demand for automation of these methods. In this study, we show that a manual SPE method used for the determination of acrylamide in brewed coffee can be converted to an autosampler compatible cartridge format and automated using a robotic autosampler controlled by user-friendly software. Calibration standards prepared in freshly brewed green coffee (un-roasted) resulted in a linear calibration curve (r2=0.99) from 1 ng/mL to 500 ng/mL. Precision of the automated SPE-LC/MS/MS method was calculated as CV = 1.7 %.
Keywords: Pyrolysis, Thermogravimetric Analysis, Gas Chromatography, Mass Spectrometery, Evolved Gas Analysis
This study shows the use of the GERSTEL MPS/TDU/CIS with pyrolysis module for generating simulated thermal gravimetric mass spectrometry data (TGA-MS) of polymer samples. This mode of operation is also referred to as evolved gas analysis (EGA). For EGA analysis, a short piece of uncoated capillary is attached from the GC inlet to the mass spectrometer. A relatively slow temperature ramp is run similar to that used for actual TGA analysis. The total ion chromatogram can be plotted as a function of temperature to produce simulated TGA-MS data. The mass spectral data is used to identify degradation products at various temperatures. Several types of polymers are examined in this study. Simulated TGA-MS data is compared with actual TGA data.
Keywords: Large Volume Injection, PTV, Water Analysis
This study shows the use of the GERSTEL Cooled Injection System (CIS) a programmable Temperature Vaporization (PTV) type inlet for large volume injection of water samples and consequent trace compound analysis. Emphasis is placed on developing method parameters in order to use the technique for routine trace analysis.
Keywords: DPX, LC/MS/MS, Sample Preparation, High Throughput Laboratory Automation
This work demonstrates the use of disposable pipette extraction (DPX) as a fast and automated sample preparation technique for the determination of barbiturates and 11-nor-9-carboxy- 9-THC (COOH-THC) in urine. Using a GERSTEL MultiPurpose autosampler (MPS) with DPX option coupled to an Agilent 6460 LC/MS/MS instrument, 8 barbiturates and COOH-THC were extracted and their concentrations determined. The resulting average cycle time of 7 min/sample, including just-in-time sample preparation, enabled high throughput screening. Validation results show that the automated DPX-LC/MS/MS screening method provides adequate sensitivity for all analytes and corresponding internal standards that were monitored. Lower limits of quantitation (LLOQ) were found to be 100 ng/mL for the barbiturates and 10 ng/mL for COOH-THC and % CVs were below 10 % in most cases.
Keywords: DPX, LC/MS/MS, Sample Preparation, Drugs of Abuse, High Throughput Lab Automation
This application demonstrates the use of Disposable Pipette Extraction (DPX) for rapid, automated sample preparation of urine samples for comprehensive LC/MS/MS screening. The combination of automated sample cleanup and introduction with mass spectrometric detection using a Scheduled MRM™ (AB SCIEX) algorithm and fast MS/MS spectral acquisition allowed high confidence compound identification based on mass spectral library matching. The automated workflow enabled monitoring of large panels of analytes (100+ drugs); detecting and quantifying these compounds in a single run. The new automated DPX-LC/MS/MS workflow provides rapid extractions, high recoveries, and minimized matrix interferences with complete automation capabilities towards high throughput chromatographic analysis.
Keywords: Automation, Total Fat, Trans Fat, Saturated Fat, Food, Gas Chromatography, Microwave, Saponification, FAMEs
Determination of total fat, saturated fat, monounsaturated fat and trans fat content in food samples is necessary for complying with applicable food labeling requirements. A typical procedure for saponification of the sample involves refluxing with sodium methoxide in methanol, followed by a second reflux with boron trifluoride in order to esterify the free fatty acids. Prior to injection into the gas chromatograph, the fatty acid methyl esters (FAMEs) must be extracted from the reaction mix and the extract must be dried. The reflux times are typically an hour. After the sample is prepared, the round bottomed flask and condenser must be cleaned. This process is laborious and time consuming, which limits sample throughput. A combined autosampler and liquid handling robot, which is commonly used for a wide variety of sample preparation techniques can be interfaced directly to a CEM Discover SP-D microwave unit. In this way, a single integrated system under MAESTRO software control can perform saponification of fats in combination with further sample preparation steps and finally introduction to a GC or HPLC system.
Keywords: GC/MS, Lab Automation, Sample Preparation, Polymers and Plastics, Toys, Toy Safety, Child Care Articles
The US Consumer Product Safety Commission’s (CPSC) Test Method CPSC-CH-C1001-09.3 , is used by testing laboratories for the determination of phthalate content in children’s toys and child care articles covered by the standard set forth in the Consumer Product Safety Improvement Act Section 108. The CPSC determined that an appropriate combination of methods of extraction and analysis is sufficient to determine the concentration of the six regulated phthalates in most consumer products. The general manual approach is to dissolve the sample completely in tetrahydrofuran, precipitate any PVC polymer with hexane, filter and then dilute the solution with cyclohexane, and analyze by Gas Chromatography-Mass Spectrometry (GC/MS). A combined autosampler and sample preparation robot commonly used for sample introduction in GC or HPLC can be used to perform a wide variety of sample preparation techniques using a single instrument set-up and associated control software. Among the autosampler capabilities controlled by MAESTRO software are filtration and centrifugation, both of which can be used to clean up polymer extracts for further analysis. The autosampler can be configured as part of a GC or LC system or can be used independently as bench top workstation. In this work, we demonstrate automated extraction of phthalates in consumer products based on CPSC method CPSC-CH-C1001-09.3 directly combined with GC/MS analysis of the extract. The entire extraction and analysis process is streamlined and helps reduce or eliminate exposure of laboratory personnel to potentially hazardous materials.
Keywords: Pyrolysis-GC/MS, Methylationm TMAH, Fatty Acid Methyl Esters, FAME, Linseed Oil, Amber
In order to improve pyrolysis chromatographic analysis of materials that release polar functional groups e.g. carboxylic acids, a simple and rapid methylation method based on TDU pyrolysis/GC-MS in the presence of tetramethylammonium hydroxide (TMAH) was developed. Linseed oil was selected as test material because of its high triglyceride content comprising both saturated and unsaturated fatty acids. Pyrolysis was performed at 500, 600 and 700°C using GERSTEL pyrolysis module (PYRO) with a heated platinum filament.
Keywords: Whiskey, Oak Barrel, Pyrolysis GC/MS
Pyrolysis GC/MS was used to profile residual solids after drying aged whiskey samples. The samples in question were both 20 years old from the same un-aged parent distillate but matured in the very different wood species of Quercus Robur and Quercus Alba. Fractionated pyrolysis chromatograms generated at 450°C were obtained for both the different whiskey residues and samples of the respective wood species. The whiskey residues showed differences in peak pattern profiles and the same differences were observed between each residue and its originating wood. Pyrolysis GC/MS could be applied to whiskey maturation investigations and can help to establish a link between the spirit non-volatile fraction and the type of wood used for maturation.
Keywords: Opiates, Opioids, Cocaine, Solid Phase Extraction, SPE, Automation, GC/MS
Analyzing blood serum for opioids, cocaine and metabolites is a routine task in forensic laboratories. The most commonly used methods involve several manual or partly-automated sample preparation steps such as protein precipitation, solid phase extraction, evaporation and derivatization followed by GC/MS or LC/MS determination. In this study a comprehensively automated method is compared with a validated, partly-automated routine method. Following manual protein precipitation, the automated method relies on a MultiPurpose Sampler (MPS) to perform all remaining sample preparation steps. These include solid phase extraction (SPE), evaporation of the eluate, derivatization and introduction to the GC/MS. Quantitative analysis of close to 170 serum samples, as well as more than 50 samples of other matrices like urine, different tissues and heart blood, was performed using both methods. Cocaine, benzoylecgonine, methadone, morphine, codeine, 6-monoacetylmorphine, dihydrocodeine and 7-aminofl unitrazepam were determined quantitatively and the methods were found to produce equivalent analytical results even near the limits of quantification
Keywords: Pesticide Residue Monitoring, QuEChERS, LC/MS/MS, Sample Preparation, DPX, Lab Automation
In this report, we describe an automated sample preparation and analysis workflow for the screening of pesticides residues in different food matrices (fruits, vegetables and spices) by LC/MS/MS. The automated cleanup of the QuEChERS extracts methodology was performed using disposable pipette extraction (DPX). Analytical methodology for confirming the presence of a variety of pesticides in various food samples was developed using a GERSTEL MultiPurpose Sampler (MPS), a combined autosampler and liquid handling robot, interfaced to an AB SCIEX QTRAP® 4500 LC/MS/MS System.
Keywords: Glyphosate, LC/MS/MS, Sample Preparation, Lab Automation, Food Safety
Glyphosate and glufosinate are widely used herbicides and, thus, there is an interest in the reliable and sensitive determination of glyphosate in water and food. These pesticides are difficult to extract and analyze because of their high polarity. In this report, we describe an automated work flow for the FMOC derivatization, sample cleanup, and LC/MS/MS analysis using a GERSTEL MultiPurpose Sampler (MPS XL) configured with an online solid phase extraction (SPEXOS) module coupled to an AB SCIEX QTRAP® 4500 system for the identification and quantitation of glyphosate, its major metabolite AMPA, and glufosinate in water and food samples. The online SPE-LC/MS/MS method allowed detection and quantitation of all target pesticides in matrix samples at 10 μg/kg concentration levels with excellent reproducibility and values well within the ±20 % range.
Keywords: Mycotoxins, LC/MS/MS, Sample Preparation, Lab Automation, Food Safety
In this report, we describe a completely automated sample preparation work multi-mycotoxin residues in different food matrices (corn, wheat) by LC/MS/MS. The extraction and cleanup was performed using a GERSTEL MultiPurpose Sampler (MPS) followed by LC/MS/MS determination using an AB SCIEX QTRAP® 4500. The automated sample preparation work flow involved centrifugation, dispersive solid phase extraction (dSPE) and evaporative concentration, providing extraction efficiencies greater than 70 % with RSDs less than 15 % for most analytes. The LC/MS/MS method was developed for screening for a panel of 14 mycotoxins (aflatoxins, trichotecenes and fuminosins) using the Scheduled MRM™ algorithm in combination with fast polarity switching, achieving excellent linearity (R2 values of 0.98 or greater) , average accuracies greater than 88 % and limits of quantitation lower than the action levels established by the EC and FDA.
Keywords: Sample Preparation, LC/MS/MS, High Throughput Laboratory Automation, DPX, Urine, Glucuronides
A major mechanism of the metabolism of many pain management drugs involves conjugation of the analyte with glucuronic acid. To ensure accurate results when drugs are determined from urine matrices, the analytes must be deconjugated which is typically performed by hydrolysis using enzymes such as beta-glucuronidase. Typical hydrolysis procedures involve long incubation periods and specified temperatures and have traditionally been performed manually. This study shows how a typical enzymatic hydrolysis procedure can be easily automated using a GERSTEL MultiPurpose Sampler (MPS), combining an automated extraction and clean-up procedure with introduction to the LC/MS/MS, in order to provide high throughput analysis of common pain management drugs.
Keywords: THC, THC-OH, THC-COOH, Serum, Solid Phase Extraction, SPE, Automation, GC/MS
This note presents a fully automated analysis system for the determination of THC and its metabolites in blood serum. Automation is based on the GERSTEL MultiPurpose Sampler (MPS) equipped for solid phase extraction and a module for automated eluate evaporation (GERSTEL mVAP). A validated, semi-automated analysis method used for routine analysis was transferred and automated using the described system. Improvements were realized such as a reduction of sample volume and the use of a smaller SPE cartridge format. The method was validated according to Society for Toxicology and Forensic Chemistry (GTFCh) guidelines. Limits of quantification below 1 ng/mL for THC and THC-OH, extraction efficiencies between 70 and 93% and RSDs between 3 and 10% were achieved.The SPE system performs sample preparation in parallel with the chromatographic run, enabling the GC/MS system to operate at maximum capacity.
Keywords: Aroma Analysis, Off-flavor, Edible Oil, Direct Thermal Desorption, Thermal Extraction, Microvial, GC/MS
This application note describes the direct thermal desorption of desirable and undesirable aroma compounds from edible oils. The oil sample is placed in a microvial from where it is directly heated using a GERSTEL Thermal Desorption Unit (TDU). Volatile compounds are transferred to the GC/MS system while leaving non-volatile oil matrix behind, preventing contamination of the GC inlet and column. Different microvial designs were evaluated and those with a slit positioned 1 cm from the bottom of the microvial were found to provide the best analyte transfer.
Keywords: Urine Hydrolysis, β-Glucuronidase, LC/MS/MS
In this report, a completely automated, 96 well plate format “Prep-and-Shoot” workflow including enzymatic hydrolysis, dilution and injection is described. A GERSTEL MultiPurpose autosampler (MPS) coupled to an AB SCIEX QTRAP® 4500 LC/MS/MS system was used for a fast enzymatic hydrolysis process (15 minutes), dilution and injection of urine samples. The procedure was applied to the analysis of multiple drug classes (e.g., opiates, opioids, benzodiazepines, muscle relaxants, hallucinogens) in urine. This automated workflow employed an ultra-pure β-Glucuronidase enzyme yielding hydrolysis efficiencies of glucuronide conjugates above 80 % for the analytes tested. The methodology developed allowed the reproducible injection and analysis of over 960 samples on the same analytical column, with % RSDs ≤ 10 %. Moreover, the combined automation of urine hydrolysis, injection and analysis allowed the system to process more than 200 samples in a day.
Keywords: Thermal Desorption, Air Analysis, VOC, JHAP
System performance of the GERSTEL TDS in conjunction with an Agilent GC/MSD system was tested using a 43 component gas calibration mixture which was developed for the Japanese Hazardous Air Pollutants (JHAP) monitoring method. A five point calibration curve was obtained for each compound (2-20 ppb@1L) with an average correlation coefficient of 0.996. Twelve replicate analyses of the mixture, where each component was present at 20 ppb@1L, gave an average percent relative standard deviation (%RSD) of 4.6.
Keywords: Automation, Chromatography, Sample Handling, Automation, Sample Preparation
The primary function of an autosampler for a chromatographic instrument is to provide unattended operation and thereby increase instrument utilization and improve sample throughput in the lab. A second important benefit of autosampler use is the improved reproducibility of analytical results compared to manual injections. Automation of sample preparation steps would have similar benefits in improving sampling reproducibility. This paper describes a software solution to control a common autosampler for HPLC or GC (MPS, GERSTEL) that provides flexible sample preparation capability without purchasing expensive laboratory robots. The following example applications illustrate the flexibility of this software for custom method generation:
Keywords: Thermal Desorption, PTV, Inlet liner, Sample Introduction
PTV inlets are often used for cryo-focussing and trapping of analytes for large volume, headspace, and thermal desorption applications. Selecting and optimizing trapping conditions for thermal desorption applications can be challenging, since often a wide variety of analytes spanning a broad boiling point range are present in each sample. For efficient, high fl ow thermal desorption systems such as the GERSTEL TDS, a variety of inlet liner configurations with different trapping characteristics are available. This study was conducted to qualify the best type of liner for the determination of alkanes, aromatics and oxygenated compounds by thermal desorption GC. Inlet liners packed with materials of different trapping strengths ranging from glass wool to adsorbents (Carbotrap™ or Tenax TA™) to special purpose multi-bed liners were used to cryo-focus test mixtures of alkanes, aromatics and oxygenates thermally desorbed from air sampling adsorbent tubes. The parameters trapping temperature and desorption fl ow were optimized for the best trapping efficiency. Guidelines are given for choosing appropriate trapping conditions for these analyte classes.
Keywords: Stir Bar Sorptive Extraction, SBSE, Twister, Thermal Desorption
The use of stir bar sorptive extraction (SBSE) as a technique to extract volatiles and semi-volatiles from polar, especially aqueous matrices, has gained more and more acceptance in several application areas. Thermal desorption, analogous to SPME, has been found to be the most suitable technique to transfer the extracted analytes into an analytical system and make them accessible for gas chromatographic analysis. PDMS coated stir bars („Twister“) have much more stationary phase and consequently bigger outer dimensions compared to SPME fibers. They do not fit into standard injection ports for thermal desorption as SPME fibers do, therefore usually a thermal desorption unit is used for this purpose. This type of unit is intentionally designed to desorb previously trapped analytes from porous polymer-packed sample tubes, or for thermal extraction of volatiles from solids. It works perfectly for Twister desorption, but may simply be somewhat oversized if this is the only purpose.This paper describes the design, performance and applicability of a new desorption unit especially designed for use with “GERSTEL Twister”. This unit is compatible with existing GC models and can be automated using a modified regular autosampler.
Keywords: Gas Chromatography, Injector, PTV, Automated Liner Exchange, Sample Preparation, Sample Clean-up, Large Volume Injection, LVI
Sample clean-up steps, which are needed in order to prepare for example environmental or food samples for pesticide analysis, are time-consuming and a potential source of errors. Simplification or elimination of such procedures is often the motivation behind the development of new analytical methods and new instrumentation. Unfortunately, analytical instruments normally do not tolerate introduction of “dirty” samples or even “dirty” extracts. For example, extracts containing suspended matter or high molecular weight compounds contaminate a GC inlet within a few injections, causing peak broadening or even loss of sensitive compounds. Reducing or eliminating clean-up steps will result in “dirty” extracts and daily – or even hourly - maintenance of the GC system.