P. Manini et al., A new method for the analysis of styrene mercapturic acids by liquid chromatography/electrospray tandem mass spectrometry, RAP C MASS, 14(21), 2000, pp. 2055-2060
A new method based on liquid chromatography/tandem mass spectrometry has be
en developed for the direct determination of specific urinary mercapturic a
cids arising from the conjugation of (R)-and (S)enantiomers of styrene 7,8-
oxide with glutathione (GSH), i.e. (R,R)- and (S,R)-N-acetyl-S-(1-phenyl-2-
hydroxyethyl)cysteine (R,R-M1 and S,R-M1) and (R,R)- and (S,R)-N-acetyl-S-(
2-phenyl-2-hydroxyethyl)- cysteine (R,R-M2 and S,R-M2), The four diastereoi
somers were separated on a C18-DB (7.5 cm, 3 mum) column using variable pro
portions of 20 mM aqueous ammonium formate buffer and methanol at a flow-ra
te of 0.5 mL/min. The analytes were ionized by electrospray, in negative-io
n mode. Operating in selected-reaction monitoring mode, linearity of the MS
response versus analyte concentration was established over 4 orders of mag
nitude, the detection limits being 0.7-1.0 mug/L for all the mercapturates.
Precision of the method determined at 50 mug/L (n = 12), expressed as rela
tive standard deviation, was respectively 3.1, 4.8 and 6.9% within the run,
intra-day and inter-day. The corresponding figures at 1.0 mg/L (n = 12) we
re respectively 2.0, 3.6 and 5.5%. The method was applied to the quantitati
ve analysis of conjugated metabolites in urine samples from workers occupat
ionally exposed to styrene, The diastereoisomers R,R-M1 and S,R-M2 accounte
d respectively for 50 and 40% of total mercapturates, whereas the proportio
n of R,R-M2 was 7% and only minor amounts of S,R-M1 were detectable. Styren
e mercapturates represented a minor fraction of total styrene metabolites,
less than 1% on average. The ratio mercapturates/main metabolites (mandelic
+ phenylglyoxylic acid) showed a bimodal distribution, the medians of the
two subgroups being 0.2 and 1%, respectively, Such subgroups are probably c
haracterized by the genetic polymorphisms of the drug-metabolizing enzymes
to be identified. Copyright (C) 2000 John Wiley & Sons, Ltd.