Headspace sampling applications

With regard to the solution approach, it is imperative that the solvent used be of the highest possible purity. Solution headspace is applicable to a much wider range of samples than the solid approach. When working with... 

In most cases the concentrations of the compounds detected by GCOH are too small for the identification experiments however, this disadvantage can be overcome when the odorants present in food are first detected in the extract by GC-O and then identified. Some of these odorants are also found by GCOH. As their odour quality, GC properties and chemical structures are known, they are easily identified in the headspace sample. In the case of parsley, a comparison of Fig. 16.2 with Table 16.5 indicates that odorant nos. 4, 6, 9, 11, 12 and 15 (Table 16.5) were known from AEDA. Further applications of GCOH are reviewed in [1]. 

A frequent use of GC with polymers is in the quantitative determination of residual monomer and solvent content, even at sub parts per million levels. This is especially important in food contact applications (e.g. printed packaging materials) where taint and odour issues are important. There are a range of sample preparation and injection techniques to deal with a vast range of samples including, for example, headspace sampling where a solid can be incubated for a period of time and then the vapours from above the solid are transferred into the GC capillary. 

Tsoukali H, Raikos N, Theodoridis G, Psaroulis D. Headspace solid phase microextraction for the gas chromatographic analysis of methyl-parathion in post-mortem human samples. Application in a suicide case by intravenous injection. Forensic Sci Int 2004 143 127-32. 

Another configuration of MAP gas-phase extraction relates to dynamic headspace sampling, often referred to as purge and trap sampling. The container can be fitted with an aperture enclosing a trap, or a sorbent, cooled by some common means. This allows the application of a prolonged, low-power irradiation, or of a multi-pulse irradiation of the sample, thus providing a means to extract all of the volatile analytes from the matrix. The contents of the trap can then be transferred (by elution for a chemical or sorbent trap, or by thermal desorption for a cold trap) to an analytical instrument, such as a... 

Clinical samples of urine, blood, expired air, and tissue have been examined using headspace sampling approaches. Thus, chlorinated organic compounds, methanol, acetone, methyl ethyl ketone, and phenols have been determined in urine. Volatile substances in urine have also been used as a guide to acute poisoning, and the determination of stimulants in urine has been proposed as screening test for field use. The determination of the concentration of blood alcohol is the most well-known application of headspace techniques to biological samples. Blood has also been examined for cyanide, methyl sulfide, and formaldehyde levels, the last as a measure of methanol intoxication. The headspace approach for blood samples overcomes the difficulties associated with the alternative direct injection of two-phase samples. 

While open tubular (OT) columns are the most popular type, both open tubular and packed columns are treated throughout, and their advantages, disadvantages, and applications are contrasted. In addition, special chapters are devoted to each type of column. Chapter 2 introduces the basic instrumentation and Chapter 7 elaborates on detectors. Other chapters cover stationary phases (Chapter 4), qualitative and quantitative analysis (Chapter 8), programmed temperature (Chapter 9), and troubleshooting (Chapter 11). Chapter 10 briefly covers the important special topics of GC-MS, derivatization, chiral analysis, headspace sampling, and solid phase microextraction (SPME) for GC analysis. 

Because liquid and headspace sampUng methods differ in kinetics, the two approaches are complementary. Equilibrium is attained more rapidly in headspace SPME than in direct-immersion SPME, because there is no liquid to hinder diffusion of the analyte onto the stationary phase. For a given sampling time, immersion SPME is more sensitive than HS-SPME for analytes predominantly present in the liquid. The reverse is true for analytes that are primarily in the headspace. Several additional factors can affect SPME and do influence the choice between immersion and headspace sampling [997]. Overall extraction with HS-SPME is apt to be lower than in direct-immersion because transfer of analytes from the sample to the gas phase seldom is quantitative. HS-SPME was compared with PT [998] and HS-GC-MS [954,999]. Application of HS-SPME eliminates many problems of other headspace techniques and extends headspace sampling to less volatile compounds due to the concentration effect at the fibre coating. Thermal desorption... 

Some typical industrial applications of HS-SPME are analysis of trace impurities in polymers and solid samples, the determination of solvent residues in raw materials, ppt odour analysis, organics in water, etc. SPME can also be used for quaUtative headspace sampling of fruit volatiles [1000]. Since equilibrium rather than exhaustive extraction occurs in the micro-extraction methods, SPME is suitable for field monitoring. 

Yang et al. described a method for the accurate and precise determination of TBT using SPME and GC-ICP-MS detection. Butyltin compounds were ethylated in aqueous solution, and the headspace sampled via a PDMS-coated fused silica SPME fibre. The application of... 

Using immersion and headspace sampling, we show in Figs. 8 through 12 that the SPME method can also be used for fragrance analysis and is applicable to a wide variety of sample types. With the aid of SPME technique, analytical chemists will be freed from the complex and time-consuming classic sample cleanup and preparation procedures that are currently used. 

A further example for application of SIDA in fragrance analysis is the quantification of skatole in soap. For this analysis, the SPME technique using 65 iim polydimethylsiloxane/divinylbenzene (PDMS/DVB) coated fiber was applied. Headspace sample was prepared as follows 1 g of soap was dispersed in 10 ml of distilled water, spiked with 1 ppm ds-skatole, and placed in a sealed 100-ml vial containing a Teflon magnetic stirring bar. The sample was equilibrated at 60°C for a period of 30 min. The fiber was carefully introduced in the headspace, and perfume oil constituents were extracted for 30 min under magnetic stirring. 

Applications The potential of a variety of direct solid sampling methods for in-polymer additive analysis by GC has been reviewed and critically evaluated, in particular, static and dynamic headspace, solid-phase microextraction and thermal desorption [33]. It has been reported that many more products were identified after SPME-GC-MS than after DHS-GC-MS [35], Off-line use of an amino SPE cartridge for sample cleanup and enrichment, followed by TLC, has allowed detection of 11 synthetic colours in beverage products at sub-ppm level [36], SFE-TLC was also used for the analysis of a vitamin oil mixture [16]. 

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