Determination of low concentrations of benzene in urine using multi-dimensional gas chromatography

A method for the determination of benzene in urine of occupationally or environmentally exposed persons was developed. The method was based on dynamic headspace, preconcentration on a solid sorbent, followed by thermal desorption and gas chromatographic determination. To achieve sufficient selectivity, we used multi-dimensional gas chromatography in combination with the inexpensive and robust flame ionisation detector. The limit of detection was 7 ng l-1 and the limit of quantification was 23 ng l-1. The linearity was good (correlation coefficient 0.999) in the range examined (20-4000 ng l-1) and the repeatability was 9%. The average recovery at low concentrations (20-400 ng l-1) was 86%. Analysis of a certified reference material of benzene in water, traceable to NIST, did not differ significantly from the certified value. Samples, frozen (-20 degrees C) in glass bottles sealed with Teflon-silicon septa, were stable for 1 year and refrigerated samples (4 degrees C) for at least 1 week. Loss of benzene during the collection and transfer of urine was investigated and found to be acceptable. The method is a cost effective and robust alternative to GC-MS and permits reliable quantification of occupational exposure and, in most cases, also of urine concentrations that can be expected from environmental exposure.