Aim To develop and validate a liquid chromatography-tandem mass spectrometric（LC/MS/MS） method for the simultaneous quantification of ephedrine and chlorpheniramine in human plasma after oral administration of a compound preparation.Methods The analytes and the internal standard,diphenhydramine,were isolated from plasma by protein precipitation with methanol,then chromatographied on a Zorbax SB-C18 column（150 mm×4.6 mm ID） using a mobile phase consisted of methanol-water-formic acid（80∶20∶0.5,v/v）,at a flow rate of 0.5 mL·min-1.A tandem mass spectrometer equipped with electrospray ionization source was used as detector and was operated in the positive ion mode.Selected reaction monitoring（SRM） using the precursor to produce ion combinations of m/z 166→115,（m/z） 275→230 and m/z 256→167 were used to quantify ephedrine,chlorpheniramine and the internal standard,respectively.Results The linear concentration ranges of the calibration curves for ephedrine and chlorpheniramine were 0.50-200 μg·L-1 and 0.050-20.0 μg·L-1,respectively.The lower limits of quantification were 0.50 μg·L-1 for ephedrine and 0.050 μg·L-1 for chlorpheniramine,individually.The intra-and inter-day relative standard deviation（RSD） across three validation runs over the entire concentration range was less than 9.3% for both ephedrine and chlorpheniramine.The inter-day accuracy（RE） was within ±3.4% for the analytes.Each sample was chromatographied within 3.3 min.The method was successfully used in pharmacokinetics study of ephedrine and chlorpheniramine in human plasma after oral administration of a compound preparation containing 5 mg ephedrine hydrochloride,1 mg chlorpheniramine maleate,50 mg phenytoin,12.5 mg theophylline,12.5 mg theobromine and 7.5 mg caffeine.No interaction among the six components was observed on their pharmacokinetic parameters.Conclusion The method was proved to be highly sensitive,selective,and suitable for pharmacokinetics investigations of different compound preparations cont
