A combination of micro-porous membrane liquid–gas extraction and solid-phase trapping for ultra trace determination of benzene in urine

A method was developed for the determination of benzene in urine. The sample was pumped through the donor channel of a membrane extraction unit with a micro-porous membrane, separating the donor channel from an identical acceptor channel purged with nitrogen. The analyte reached the acceptor channel by diffusion through the membrane and was then swept by the carrier to a solid sorbent tube, where it was trapped. The analyte was subsequently thermally desorbed and analyzed by gas chromatography (GC) with mass selective detection (MS). After optimization, the recovery was close to quantitative, or 95%. Purging the membrane unit with pure water inbetween the samples eliminated any memory effects. The linearity was good in the concentration range examined (20–4000 ng l–1), with a correlation coefficient of 0.9996. The repeatability at 50 ng l–1 and 400 ng l–1 was 1.4% and 1.2%, respectively. The limit of detection was 12 ng l–1 and the limit of quantification 35 ng l–1. This enables assessment of benzene exposures of occupationally exposed subjects, of smokers and the majority of the general population. The developed method can be easily automated.