Equilibrium sorptive enrichment on poly(dimethylsiloxane) particles for trace analysis of volatile compounds in gaseous samples

A novel approach for sample enrichment, namely, equilibrium sorptive enrichment (ESE), is presented. A packed bed of sorption (or partitioning) material is used to enrich volatiles from gaseous samples. Normally, air sampling is stopped before breakthrough occurs, but this approach is not very successful for weakly retained compounds (volatiles) as early breakthrough occurs. In ESE, sampling is continued until all compounds of interest are in equilibrium with the sorptive material. This allows accurate sampling of volatiles and enrichment at the maximum attainable sensitivity. However, due to the equilibrium nature of ESE, it is limited to samples with a constant concentration over the sampling time. This requirement is easily met for those compounds with short equilibration times (volatiles). Because of the nature of the sorption mechanism, which is basically dissolution, all compounds partition independently into the sorbent (stationary phase) and displacement effects do not occur. This is a great advantage over adsorption materials. Additionally, theory allows the calculation of enrichment factors from literature retention indexes. Moreover, ESE also benefits from the features of sorption materials such as a very high inertness and interference-free blanks. The performance of ESE is illustrated with the analysis of several analytes including the epoxides ethylene oxide and epichlorohydrin in real-life air sampling