Twister® or Stir-Bar Sorptive Extraction is an extraction method whereby a magnetic stirrer bar coated with sorbents stirs a liquid sample during the extraction process. This method allows very high concentration of the analytes, particularly for aqueous matrices. For the actual analysis, the Twister bars are heated in a Twister Desorption Unit (TDU) and the analytes are passed to a GC-MS/O system.
SPME is a technique that is fast and easily automated in conjunction with gas chromatography. A fiber coated with adsorbents that is built into a syringe needle is exposed to the sample. Analytes concentrate on the fiber and these are subsequently thermally desorbed in the injector. Analysis of the headspace above the sample (headspace-SPME) and immersion of the fiber in aqueous samples are possible. A wide range of adsorbents for the fibers allows optimization of the extraction for specific analytes. SPME is particularly useful for challenging matrices, requires little sample preparation, and can thus be easily automated.
The technique of thermodesorption is used when odorants and other volatile substances have to be analyzed in solid, paste-like, and even liquid matrices. This technique is especially useful for challenging matrices such as plastics, adhesives, fibers, and resins, as well as for measuring and identifying thermally desorbed or liberated odors. The desorption temperature can be selected in the range from 50°C to 300°C as can the duration. Analytes are collected via cryofocusing with liquid nitrogen and are subsequently analyzed by GC-MS/O. The desorption and measurements are automated.
Pyrolysis, in contrast, has numerous applications: Thermal decomposition processes, such as those involving the formation of volatile and odor-active degradation products, can be analyzed as a function of temperature. The pyrolysis temperature can be freely selected up to 1000°C. An example of an application is the identification of odors in the fumes of different sorts of wood. Another application is Py-GC-MS coupling for the characterization of polymer materials. Here the decomposition products allow conclusions to be drawn about the composition of a polymer.
Highly volatile odors are often difficult to analyze using standard analytical methods. In headspace analysis a defined gas volume from the headspace of a sample is removed and injected into a GC. Thermally labile and highly volatile substances in a wide variety of matrices can be readily analyzed using this method. Large numbers of samples can be analyzed in an automated system under defined, accurately reproducible conditions such as incubation time and incubation temperature. Also, an autosampler system allows reagents and standards to be added and other sample preparation steps automated.
SAFE is a special high vacuum distillation technique used for the isolation of thermally labile flavors under gentle conditions. A sample is extracted with solvent and passed via a dropping funnel into a high vacuum at 40-50°C. Volatile substances and the solvent are completely evaporated and transferred to a flask cooled by liquid nitrogen. The non-volatile components remain behind. A unique aspect of SAFE is the equipment design that allows very efficient, low-loss processing. The recovered sample extracts are usually concentrated under mild conditions and then analyzed using a variety of analytical methods such as GC-MS and GC-Olfactometry.
LC-MS/MS (liquid chromatography coupled with tandem mass spectrometry) allows non-volatile analytes to be identified and quantified. This technique is used, for example, for the identification of odor precursors and also for flavor analysis.