Keywords: PTV Injection, Multicolumn Switching, Multidimensional GC, Cryotrapping, Capillary GC/MS, industrial Applications
The separation and analysis of low concentrations of organic compounds in complex sample matrices, such as petroleum products, waste and drinking water, food, beverages and pharmaceutical products is a rather complex analytical problem. Current methods are hampered by insufficient resolution obtained by single capillary columns even if they have rather high plate numbers. In this paper the potential of a combination of programmed temperature sample introduction and mass flow controlled multicolumn dual oven capillary gas chromatography and on-line mass spectrometry will be discussed and illustrated. The effect of cold trapping in between the columns for components with a moderate volatility will be demonstrated for different applications dealing with the determination of trace impurities in various main products such as gasoline, aromatics, steroids and aniline.
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: 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: 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: 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: 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: 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: 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: 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: 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: Biodiesel, Automation, ASTM D6584-07
Biodiesel is defined as mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats which conform to ASTM D6751 specifications for use in diesel engines. Biodiesel is produced from the fat or oil by transesterification. Glycerin is an unwanted byproduct of the reaction and must be removed from the final product. ASTM Method D6584-07 measures the amount of residual free and bonded (mono-, di-, and triglycerides) glycerin in the biodiesel fuel. Standard and sample preparation, which requires a derivatization step, can be laborious and time consuming. Using the GERSTEL MPS Dual Rail PrepStation and MAESTRO control software, the entire method, including standards and sample preparation, derivatization, dilution, and analysis can be fully automated. This paper shows the details of the automation.
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: 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: 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: 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.