Simultaneous quantitative analysis of dextromethorphan, dextrorphan and chlorphenamine in human plasma by liquid chromatography–electrospray tandem mass spectrometry

A sensitive and accurate HPLC‐MS/MS method was developed for the simultaneous determination of dextromethorphan, dextrorphan and chlorphenamine in human plasma. Three analytes were extracted from plasma by liquid–liquid extraction using ethyl acetate and separated on a Kromasil 60‐5CN column (3 µm, 2.1 × 150 mm) with mobile phase of acetonitrile–water (containing 0.1% formic acid; 50:50, v/v) at a flow rate of 0.2 mL/min. Quantification was performed on a triple quadrupole tandem mass spectrometer in multiple reaction monitoring mode using positive electrospray ionization. The calibration curve was linear over the range of 0.01–5 ng/mL for dextromethorphan, 0.02–5 ng/mL for dextrorphan and 0.025–20 ng/mL for chlorphenamine. The lower limits of quantification for dextromethorphan, dextrorphan and chlorphenamine were 0.01, 0.02 and 0.025 ng/mL, respectively. The intra‐ and inter‐day precisions were within 11% and accuracies were in the range of 92.9–102.5%. All analytes were proved to be stable during sample storage, preparation and analytic procedures. This method was first applied to the pharmacokinetic study in healthy Chinese volunteers after a single oral dose of the formulation containing dextromethorphan hydrobromide (18 mg) and chlorpheniramine malaeate (8 mg). Copyright © 2013 John Wiley & Sons, Ltd.