Keywords: Sample Preparation, Lab Automation, LC/MS/MS, SBSE
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 in combination with GC-MS or LC-MS. 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 . The dispersive Solid Phase Extraction (SPE) used to clean up these extracts can leave co-extractants, which can result in interferences such as ion suppression with the analytical results.
Stir bar sorptive extraction (SBSE) is a sorptive extraction technique based on polydimethylsiloxane (PDMS) coated stir bars. SBSE was developed to concentrate nonpolar analytes from aqueous solutions, and has recently been shown to effectively extract and concentrate PAHs from QuEChERS extracts while eliminating matrix interference for GC/MS analysis .
In this study we describe the potential benefits of using SBSE to concentrate pesticides from QuEChERS extracts and provide additional clean-up resulting in less matrix interference during LC-MS/MS.
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: 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: Capillary Gas Chromatography, Mass Selective Detection, Multidimensional GC/MSD, Blood Lipids, Human Milk, Furan Fatty Acids
The fatty acid composition of plasma, red blood cells and platelets were investigated. Human milk was analyzed and the fatty acid composition compared to cow’s milk. After lipid extraction and transesterification the methyl esters were analyzed without any further pre-analytical separation steps involved. Using a multidimensional GC/MSD System with cooled injection (CIS/PTV) and flow controlled column switching with cold trapping in between, the methyl esters of furan fatty acids were directly identified by means of their mass spectra. From the ten samples of human milk analyzed only one contained the furan fatty acid 12,15- epoxy-13,14-dimethyleicosa-12,14-dienoic acid (F-acid 10, Figure 1), which was also present in the cow’s milk sample. Furan fatty acids were found in all blood samples in differing relative amounts. F-acids 5,8 and 10 were detected in red blood cells, F-acids 8 and 10 in plasma and in platelets only F-acid 10 was found so far.
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, 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: 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: QuEChERS, LC/MS/MS, Sample Preparation, Lab Automation
QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation methods were developed to help monitor pesticides in a range of food samples . These methods are quite labor intensive, however, since they include several manual steps, such as shaking, centrifugation, and dispersive SPE. If dispersive SPE clean up of QuEChERS type extracts could be automated, laboratory productivity for monitoring pesticide residues in food could be improved significantly. In the work presented here, an automated dispersive SPE clean-up method for QuEChERS extracts was developed and combined with LC/MS/MS analysis of the cleaned extracts. Extracts were prepared with commercially available kits from Agilent Technologies. Automation was achieved using a GERSTEL MPS XL PrepStation configured with an Anatune CF-100 centrifuge. Analytical methodology for confirming the presence of a variety of pesticides in a range food samples was developed using an Agilent G6460A Triple Quadrupole Mass Spectrometer. The sensitivity and selectivity of LC/MS/MS enable sufficiently low limits of determination to meet acceptance criteria for reporting the maximum residue levels (MRLs) that are established by regulatory agencies. The ability to automate the dispersive SPE clean-up of QuEChERS extracts combined with introduction of the cleaned extract directly to the LC/MS/MS system results in improved laboratory productivity by streamlining the complete analytical process.
Keywords: PAH, seafood, QuEChERS, SBSE, GERSTEL Twister
The Deepwater Horizon oil rig explosion and the subsequent massive oil spill was one of the worst offshore oil catastrophe in United States history and is and impacted fragile ecosystems, air and water quality, and food supplies.
Protecting humans from consuming foods contaminated with oil, while minimizing economical impacts for fisheries, is presenting several challenges. The current protocol for screening seafood harvested from the gulf is organoleptic testing followed by polycyclic aromatic hydrocarbons (PAHs) testing using NOAA Method 2004. It is generally thought that improved testing strategies will be needed to meet state screening requirements. A recent EPA Region 7 study has shown that Stir Bar Sorptive Extraction (SBSE) is an effective and fast technique for trace PAH determination in water. The goal of this study is to determine if using a QuEChERS solvent extraction in conjunction with SBSE can meet regulatory limits of detection and requirements established for precision and accuracy. Preliminary data show linear calibration for PAHs from 1-250 ng/g tissue in matrix matched extracts. Triplicate analyses estimates recoveries at 107 % ± 5 % RSD in fish tissue spiked with 2.5 or 25 ng/g PAH standards. It is also estimated that 40-60 homogenized samples/analyst/day can be analyzed using this improved method.
Keywords: PAH, seafood, QuEChERS, SBSE, GERSTEL Twister
This method uses a QuEChERS (quick, easy, cheap, effective, rugged, and safe) single-step acetonitrile (ACN) extraction and salting out liquid-liquid partitioning to extract PAHs from seafood tissue. Stir Bar Sorptive Extraction (SBSE) is then used as a combined cleanup and concentration step, eliminating organic acids and other polar and high molecular weight matrix components and providing a substantial concentration factor to easily meet regulatory limits of detection and requirements established for precision and accuracy for determination of PAHs in seafood tissue. In brief, 3g of a homogenized seafood tissue sample in water is extracted with ACN in a 50 mL centrifuge tube followed by addition of 6.0 g MgSO4 and 1.5 g sodium acetate which is shaken and centrifuged. A portion of the ACN extract (upper layer) is added to a 10 mL vial with 4 mL 0.1 M NaHCO3 and a GERSTEL Twister™ stir bar and stirred to extract and concentrate the PAHs. The Twister stir bar is transferred to a thermal desorption tube in an autosampler tray for analysis by gas chromatography/mass spectrometry (GC/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: 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, 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: 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: 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: 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: 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: 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: 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: 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: 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: Food, Flavor, Fragrance, Beverage
Below is a list of publications on SBSE for your reference. These cannot be downloaded due to Copyright protection.
Determination of stale-flavor carbonyl compounds in beer by stir bar sorptive extraction with in-situ derivatization and thermal desorption-gas chromatography-mass spectrometry.Ochiai, N. et al. J. Chromatogr. A. 2003 986,101-110.
Analysis of volatiles of malt whiskey by solid-phase microextraction and stir bar sorptive extraction. Demyttenaere, J. C. R. et al. J. Chromatogr. A. 2003, 985, 221-232.
Application of stir sorptive extraction for wine analysis. Hayasaka, Y. et al. Anal. Bioanal. Chem. 2003, 375, 948-955
Monitoring and fast detection of mycotoxin-producing fungi based on headspace solid-phase microextraction and headspace sorptive extraction of volatile metabolites. Demyttenaere, J. C. R et al. J. Chromatogr. A. 2003 985, 127-135.
Application of headspace-mass spectrometry for differentiating sources of olive oil. Marcos Lorenzo, I. et al. Anal. Bioanal. Chem. 2002, 374, 1205-1211
Headspace Sorptive Extraction (HSSE), Stir Bar Sorptive Extraction (SBSE), and Solid Phase Microextraction (SPME) Applied to the Analysis of Roasted Arabica Coffee and Coffee Brew, Carlo Bicchi, Cristina Iori, Patrizia Rubiolo, Pat Sandra J. Agric. Food Chem. 2002, 50, 499-459
Analysis of Volatile Esters of Malt Whisky Using Solid Phase Microextraction and Dynamic Headspace J.C.R. Demyttenaere, J.I. Sánchez Martínez, J.J. Téllez Valdés, R. Verhé, P. Sandra Symposium on Capillary Chromatography and Electrophoresis-Riva del Garda, Italy (2002)
Headspace GC-SCD monitoring of low volatile sulfur compounds during fermentation and in wine D. Rauhut, H. Kürbel, K. MacNamara, M. Grossman Analusis, 1998, 26, 142-145
Determination of Contaminants in Wine using Stir Bar Sorptive Extraction (SBSE) F. David, A. Tredoux, E. Baltussen, A. Hoffman, P. Sandra 23rd International Symposium on Capillary Chromatography-Riva del Garda, Italy (2000)
Stir Bar Sorptive Extraction Applied to Lemon Flavored Beverages A.G.J. Tredoux, H.H. Lauer, Th. Heideman, P. Sandra 23rd International Symposium on Capillary Chromatography-Riva del Garda, Italy (2000)
The Determination of Benzoic Acid in Lemon Flavored Beverages by Stir Bar Sorptive Extraction-CGC-MS Andreas G.J. Tredoux, Henk H. Lauer, Theo Heideman, Pat Sandra J. High Resol. Chromatogr. 2000, 23, (11) 644-646
Study on Highly Sensitive Analysis of Flavor Compounds in Beverage by Gas Chromatography/Mass Spectrometry with Static and Dynamic Headspace Technique Nobuo Ochiai, Norihiro Sakui, Shigeki Daishima, Daniel B. Cardin 22nd International Symposium on Capillary Chromatography-Gifu, Japan (1999)
Analysis of Ethyl Carbamate by Multi-Dimensional Gas Chromatography/Mass Spectrometry in Alcohol Beverages using Solid Phase Extraction Eshwar Jagerdeo, Sumar Dugar Poster PittCon 2001
Simultaneous determination of preservatives in beverages, vinegar, aqueous sauces, and quasi-drug drinks by stir-bar sorptive extraction (SBSE) and thermal desorption GC-MS Nobuo Ochiai, Kikuo Sasamoto, Masahiko Takino, Satoru Yamashita, Shigeki Daishima, Arnd C. Heiden, Andreas Hoffmann Anal Bioanal Chem (2002) 373:56-63
The Loss of Volatile Esters from Cookies S. Heiderich, Gary Reineccius Perfumer & Flavorist. Vol. 26, November/December 2001
High Capacity Headspace Sorptive Extraction B. Tienpont, F. David, D. Bicchi, P. Sandra J. Microcolumn Separations, 12(11) 577-584 (2000)
Cocoa Liquor Aroma Quality by Rapid Thermal Desorption-GC/MS Analysis Alexander Hässelbarth, Marion Schulze, Frank Ullrich Symposium on Capillary Chromatography and Electrophoresis-Riva del Garda, Italy (2002)
Flavor, Fragrance and Odor Analysis Ray Marsili, Ed. Marcel Dekker (2001)
Stir bar sorptive extraction (SBSE)-enantio MDGC-MS- a rapid method for the enantioselective analysis of chiral flavour compounds in strawberries Mirjam Kreck, Annette Scharrer, Steffi Vilke, Armin Mosandl Eur Food Res Technol (2001) 213:389-394
Enantioselective analysis of monoterpene compounds in essential oils by stir bar sorptive extraction (SBSE)-enantio-MDGC-MS Mirjam Kreck, Annette Scharrer, Steffi Bilke, Armin Mosandi Flavour Fragr. J. 2002; 17:32-40
Headspace Sorptive Extraction (HSSE) B. Tienport, F. David, C. Bicchi, P. Sandra 23rd International Symposium on Capillary Chromatography-Riva del Garada, Italy (2000)