Column liquid chromatography for the simultaneous determination of the enantiomers of loxoprofen sodium and its metabolites in human urine.

A method for simultaneously quantitating the enantiomers in the alpha-substituted propionic acid moiety of loxoprofen and its two monohydroxy metabolites, trans- and cis-alcohols, by column liquid chromatography was described. Loxoprofen and its metabolites were readily converted to the amides by condensation with a chiral reagent (1S)-1-(4-dimethyl-aminonaphthalen-1-yl) ethylamine. The diastereoisomers were separated on a normal-phase column with n-hexane-ethylacetate (68:32) as a mobile phase and detected with a fluorescence detector. The established method was applied to the determination of the enantiomers of these compounds in the urine of human subjects having received loxoprofen sodium. The results indicated that the three compounds were largely composed of the (2S)-isomer, in accordance with previous findings in rats.