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.