Matrix interferences in the analysis of benzene in urine

The analysis of benzene in urine of the general population or of exposed wo rkers can be performed with different methods using the 'purge and trap' or 'solid-phase microextraction' techniques in combination with gas chromatog raphic analysis and photoionisation or mass spectrometric detection. The pu blished results, however, are deeply conflicting. Differences in sample pre paration by different research groups and our own preliminary observations prompted us to investigate pre-analytical and analytical factors potentiall y capable of modifying the urinary benzene quantification results. Benzene concentrations were measured in 20 urine samples in relation to different c onditioning conditions (at 24, 40 and 80 degrees C) and at basic or acid pH . Urinary protein concentrations were measured in the same samples. Urine h eating at 80 degrees C yields benzene concentrations on average five times higher than at 24 degrees C. On acidification of urine, the benzene release d increases up to 28-fold in comparison to that obtained at uncorrected 'ph ysiological' pH. Despite a widely scattered data distribution, a statistica lly significant linear correlation was found between 'heat-released' and 'a cid-labile' benzene values. There was no correlation between total urinary proteins present in 'physiological' concentrations (between 12 and 110 mg/l ) and the different kinds of benzene in urine. Our results could perhaps be explained if it is supposed that part of the benzene in urine is absorbed onto sediment, or bound to specific proteins, or derived from parent molecu les and is released with pH modification or heat administration. Our observ ations may also help to explain why the urinary benzene concentrations repo rted by different investigators vary considerably even when environmental l evels are comparable. (C) 1999 Elsevier Science B.V. All rights reserved.