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Vacuum-assisted headspace solid phase microextraction: Improved extraction of semivolatiles by non-equilibrium headspace sampling under reduced pressure conditions

Elefteria Psillakis, Evangelia Yiantzi, Lucia Sanchez-Prado, Nicolas Kalogerakis

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Summary

A new headspace solid-phase microextraction (HSSPME) procedure carried out under vacuum conditionsis proposed here where sample volumes commonly used in HSSPME (9 mL) were introduced intopre-evacuated commercially available large sampling chambers (1000 mL) prior to HSSPME sampling.The proposed procedure ensured reproducible conditions for HSSPME and excluded the possibility ofanalyte losses. A theoretical model was formulated demonstrating for the first time the pressure dependenceof HSSPME sampling procedure under non equilibrium conditions. Although reduced pressureconditions during HSSPME sampling are not expected to increase the amount of analytes extracted atequilibrium, they greatly increase extraction rates compared to HSSPME under atmospheric pressuredue to the enhancement of evaporation rates in the presence of an air-evacuated headspace. The effect islarger for semivolatiles whose evaporation rates are controlled by mass transfer resistance in the thin gasfilm adjacent to the sample/headspace interface. Parameters that affect HSSPME extraction were investigatedunder both vacuum and atmospheric conditions and the experimental data obtained were used todiscuss and verify the theory. The use of an excessively large headspace volume was also considered. Theapplicability of Vac-HSSPME was assessed using chlorophenols as model compounds yielding linearitiesbetter than 0.9915 and detection limits in the low-ppt level

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