Simultaneous quantitation of paracetamol, caffeine, pseudoephedrine, chlorpheniramine and cloperastine in human plasma by liquid chromatography–tandem mass spectrometry

A rapid and sensitive method based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) for the simultaneous quantitation of paracetamol, caffeine, pseudoephedrine, chlorpheniramine and cloperastine in human plasma has been developed and validated. After sample preparation by liquid–liquid extraction, the analytes and internal standard (diphenhydramine) were analyzed by reversed-phase HPLC on a Venusil Mp-C18 column (50 mm × 4.6 mm, 5 μm) using formic acid:10 mM ammonium acetate:methanol (1:40:60, v/v/v) as mobile phase in a run time of 2.6 min. Detection was carried out by electrospray positive ionization mass spectrometry in the multiple-reaction monitoring mode. The method was linear for all analytes over the following concentration (ng/ml) ranges: paracetamol 5.0–2000; caffeine 10–4000; pseudoephedrine 0.25–100; chlorpheniramine 0.05–20; cloperastine 0.10–40. Intra- and inter-day precisions (as relative standard deviation) were all ≤11.3% with accuracy (as relative error) of ±5.0%. The method was successfully applied to a study of the pharmacokinetics of the five analytes after administration of a combination oral dose to healthy Chinese volunteers.