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: 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: 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: 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: 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: 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: 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: 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: 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: 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.