Simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography tandem mass spectrometry

Quantitative analysis of therapeutic compounds and their metabolites in bio logical matrix (such as plasma serum or urine) nowadays requires sensitive and selective methods to allow the determination of concentrations in the n g/ml range. A new on-line LC-MS-MS method using atmospheric pressure chemic al ionisation (APCI) as interface for the simultaneous determination of nif edipine (MF) and its metabolite in human plasma, dehydronifedipine (DMF) ha s been developed. The compounds were extracted from plasma using solid-phas e extraction (SPE) on disposable extraction cartridges (DECs). The SPE oper ations were performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with phenyl modified sil ica was first conditioned with methanol and water. The washing step was per formed with water. Finally, the analytes were successively eluted with meth anol and water. The liquid chromatographic (LC) separation of NIF and DNIF was achieved on a RP-ls stationary phase (4 mu m). The mobile phase consist ed of methanol-50 mM ammonium acetate solution (50:50, v/v). The LC was the n coupled to tandem mass spectrometry with an APCI interface in the positiv e ion mode. The method developed was validated. The absolute recoveries evaluated over the whole concentration range were 95+/-2% and 95+/-4% for NIF and DNIF, re spectively. The method was found to be linear in the 0.5-100 ng/ml concentr ation range for the two analytes (r(2)=0.999 for both NIF and DNIF). The me an R.S.D. values for repeatability and intermediate precision were 2.9 and 3.0% for NIF and 2.2-4.7% for the metabolite. The method developed was succ essfully used to investigate the plasma concentration of NIF and DNIF in th e pharmacokinetic studies. (C) 1998 Elsevier Science BN. All rights reserve d.