Liquid chromatography-tandem mass spectrometry method of loxoprofen in human plasma

A rapid, sensitive and selective liquid chromatography-electrospray ionization mass spectrometric method for the determination of loxoprofen in human plasma was developed. Loxoprofen and ketoprofen (internal standard) were extracted from 20 mu L of human plasma sample using ethyl acetate at acidic pH and analyzed on an Atlantis dC(18) column with the mobile phase of methanol-water (75:25, v/v). The analytes were quantified in the selected reaction monitoring mode. The standard curve was linear over the concentration range of 0.1-20 mu g/mL with a lower limit of quantification of 0.1 mu g/mL. The coefficient of variation and relative error for intra- and inter-assay at four quality control levels were 2.8-5.2 and 4.8-7.0%, respectively. The recoveries of loxoprofen and ketoprofen were 69.7 and 67.6%, respectively. The matrix effects for loxoprofen and ketoprofen were practically absent. This method was successfully applied to the pharmacokinetic study of loxoprofen in humans. Copyright (C) 2009 John Wiley & Sons, Ltd.