Headspace analysis adsorption-desorption

Headspace analysis involves examination of the vapours derived from a sample by warming in a pressurized partially filled and sealed container. After equilibration under controlled conditions, the proportions of volatile sample components in the vapours of the headspace are representative of those in the bulk sample. The system, which is usually automated to ensure satisfactory reproducibility, consists of a thermostatically heated compartment in which batches of samples can be equilibrated, and a means of introducing small volumes of the headspace vapours under positive pressure into the carrier-gas stream for injection into the chromatograph (Figure 4.25). The technique is particularly useful for samples that are mixtures of volatile and non-volatile components such as residual monomers in polymers, flavours and perfumes, and solvents or alcohol in blood samples. Sensitivity can be improved by combining headspace analysis with thermal desorption whereby the sample vapours are first passed through an adsorption tube to pre-concentrate them prior to analysis. 

Breath Collection in bags, adsorption on silica gel desorption to headspace vial analysis of headspace gases GC/MS-SIM 0.1 ppb NR Gruenke et al. 1986... 

In headspace SPME, there are two processes involved the release of analytes from their matrix and the adsorption of analytes by the liber coating. The volatile organic analytes are extracted, concentrated in the coating and transferred to the analytical instrument for desorption and analysis. In comparison to well-established techniques, SPME is inexpensive, solvent free, and convenient. In addition, because relatively mild conditions can be used, i.e., systems at equilibrium and temperatures less than 50°C, SPME gives a better quantitative estimate of the flavor profile. ... 

Particularly in food applications headspace SPME is preferred to avoid possible contamination of the headspace system by non-volatile food components. Also SPME analysis is quite sensitive to experimental conditions. In addition to the stationary phase, sample, volume concentration of odorants, sample matrix and uniformity as well as temperature and time of the adsorption and desorption processes influence the yield. In quantitative SPME analysis these influences are eliminated by the use of labelled internal standards (cf. 5.2.6.1). 

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