ANALYSIS OF DI-N-BUTYLPHTHALATE BIOTRANSFORMATION IN CATTLE BY LIQUIDCHROMATOGAPHY ION-TRAP MASS-SPECTROMETRY MASS-SPECTROMETRY

The nature of products of contamination intake were investigated in ca ttle dosed with [C-14] di-n-butylphthalate (DBP). Radio-labelled metab olites were extracted from bile, faeces, plasma and urine onto solid-p hase media, fractionated by ion-exchange chromatography, separated by reverse phase HPLC and analysed by negative ion atmospheric pressure c hemical ionization mass spectrometry(n) (LCQ, Finnigan). All matrices contained a common major metabolite [deprotonated molecular ion (M-H)( -) m/z 221] which coeluted with and had an identical daughter ion spec trum to reference monobutylphthalate (MBP). MBP was metabolised to a b eta-glucuronidase sensitive compound (M-H)(-) m/z 397 whose spectrum c ontained daughter ions (m/z 175 and 221) consistent with the parent gl ucuronide. A further three beta-glucuronidase resistant radio-labelled metabolites were also produced (M-H- mit 165, 193 and 237); compariso n of daughter ion spectra with those of reference MBP and phthalic aci d indicated identity with phthalic acid, monoethylphthalate (MEP) and monohydroxybutylphthalate (MHBP) respectively. The presence of a benzo ate daughter ion (m/z 121) in all spectra was indicative of side chain biotransformation. Both MBP and MEP contained a phthalate daughter io n (m/z 165) indicating loss of a butyl and ethyl side chain respective ly. A daughter ion of mit 89 derived from the side chain provided evid ence that the third metabolite was MHBP. Incubation of DBP with isolat ed bovine hepatocytes produced the same metabolites and provided relat ively clean samples for LC/MSn analysis. Detection of these DBP metabo lites in meat or dairy food products will provide evidence for environ mental exposure and biotransformation in vivo, whereas the presence of the parent compound would suggest contamination during food processin g and packaging. (C) Crown Copyright 1998. Replaced with the permissio n of the Controller of Her Majesty's Stationery Office.