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Effect of Henry's law constant and operating parameters on vacuum-assisted headspace solid phase microextraction

Elefteria Psillakis, Nicolas Kalogerakis, Evangelia Yiantzi, Antonia Mousouraki

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Year 2012
Type of Item Peer-Reviewed Journal Publication
Bibliographic Citation E. Psillakis, A. Mousouraki, E. Yiantzi, N. Kalogerakis, "Effect of Henry's law constant and operating parameters on vacuum-assisted headspace solid phase microextraction ",J.of Chroma. A,vol.1244,pp. 55-60,2014.doi:10.1016/j.chroma.2012.05.006
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Nonequilibrium headspace solid-phase microextraction (HSSPME) sampling under vacuum conditionsmay dramatically improve extraction kinetics compared to regular HSSPME at room temperature. Thispaper investigates the effects of organic analyte properties and sampling parameters (headspace volumeand sample agitation) on vacuum-assisted HSSPME (Vac-HSSPME). It was found that at room temperature,acceleration effects on extraction rates induced by reducing the total pressure of the samplecontainer are important for those compounds where the Henry’s law constant, KH, is close or belowthe reported threshold values for low KH solutes. For these compounds evaporation rate is controlled bymass transfer resistance in the thin gas-film adjacent to the gas/sample interface and reducing the totalpressure will increase evaporation rates and result in a faster overall extraction process. Conversely, foranalytes with an intermediate KH value, Vac-HSSPME is not expected to improve extraction rates comparedto regular HSSPME given that mass transfer resistance in the liquid-film becomes important. Inaccordance with the theory, at equilibrium, the amount of analyte extracted by the SPME fiber is notaffected by the pressure conditions inside the sample container. Furthermore, Vac-HSSPME extractionkinetics for low KH analytes were marginally affected by the tested change in headspace volume as evaporationrates dramatically increase under reduced pressure conditions and the sample responds muchfaster to the concentration drops in the headspace when compared to regular HSSPME. At equilibriumhowever, increasing the headspace volume may result in a loss of sensitivity for Vac-HSSPME similarto that observed for regular HSSPME. As expected, stirring the liquid sample was found to improve Vac-HSSPME. Finally, the method yielded a linearity of 0.998 and detection limits in the ppt level. The precisionvaried between 1.8% and 8.4%.

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