Downsizing vacuum-assisted headspace solid phase microextraction

Abstract

Recently, we proposed a new headspace solid-phase microextraction (HSSPME) procedure, termed vacuum-assisted HSSPME (Vac-HSSPME), where headspace sampling of 10 mL aqueous sample volumes took place in 500 or 1000 mL sample containers under vacuum conditions. In the present study, we downsized the extraction device to a 22 mL modified sample vial and concluded that changes in the final total pressure of the pre-evacuated vial following sample introduction were sufficiently low to allow efficient Vac-HSSPME sampling. The downsized extraction device was used to extract five low molecular weight polycyclic aromatic hydrocarbons and several experimental parameters were controlled and optimized. For those compounds whose mass transfer resistance in the thin gas-film adjacent to the gas/sample interface controls evaporation rates, reducing the total pressure during HSSPME sampling dramatically enhanced extraction kinetics in the 22 mL modified vial. Humidity was found to affect the amount of naphthalene (intermediate KH compound) extracted by the fiber at equilibrium as well as impair extraction of all analytes at elevated sampling temperatures. All the same, the high extraction efficiency and very good sensitivity achieved at room temperature and within short sampling times comprised the most important features of Vac-HSSPME in this downsized extraction device. Analytically, the developed method was found to yield linear calibration curves with limits of detection in the low ng L−1 level and relative standard deviations ranging between 1.3 and 5.8%. Matrix was found not to affect extraction.