Gas chromatography-electron capture determination of styrene-7,8-oxide enantiomers

The enantiomers of styrene-7,8-oxide (phenyloxirane, SO) were determined us ing a method based on base catalysed hydrolysis with sodium methoxide. The oxirane ring opening resulted in formation, without racemisation, of the en antiomeric pairs of the two regional isomers, 2-methoxy-1-phenylethanol and 2-methoxy-2-phenylethanol. The structure of these regional isomers was con firmed by gas chromatography-mass spectrometry (GC-MS) and proton nuclear m agnetic resonance (H-1-NMR). To improve sensitivity of determination, the f ormed methoxy alcohols were subsequently derivatised with pentafluoropropio nic anhydride enabling electron capture detection. This derivatization proc eeded also without racemisation and the formed pentafluoropropionyl derivat ives were separated on two serially coupled columns, a non-chiral AT 1705 a nd a chiral CP Chirasil-Dex-CB. As internal standard 2S,3S-(-)-2-methyl-3-p henyloxirane was used. The limit of quantitation of the method was 0.2 muM. The repeatability of the method was assessed at two concentration levels ( 2.5 and 25 muM) and ranged from 6 to 9% for both enantiomers. The method wa s applied to the determination of the rate and enantioselectivity of the cy tochrome P-450 dependent oxidation of styrene to SO enantiomers in human li ver microsomes. (C) 2000 Elsevier Science B.V. All rights reserved.