Column-switching liquid chromatographic determination of ML-1035 sulphoxide and its sulphone and sulphide metabolites in rat urine

A fully automated column-switching LC assay has been developed for the simultaneous determination of a gastroprokinetic agent, ML-1035 sulphoxide, and its sulphone and sulphide metabolites in rat urine. ML-1035 Sulphoxide is a metoclopramide analogue. The method involved direct injection of a diluted urine sample into a CN extraction column for sample clean-up. Polar urine components, including proteins, were flushed to waste. The retained compounds were then eluted onto a C 8 analytical column for further separation and analysis by fluorescence detection. After the subsequent washing and re-equilibration with a sequence of three solvent mixtures, the extraction column was ready for the next injection. The recovery of the compounds from the extraction column was 85–90%. The limit of quantitation for all compounds of interest was 25 ng ml −1 or lower, using a 100 μl specimen of urine. Good inter-day precision (2.1–10.0%), accuracy (0.3–18.0%), and linearity were obtained for all compounds over a range of 25–1000 ng ml −1. The applicability of the LC method was validated with urine samples from rats that had received ML-1035 sulphoxide.