Analitical Methods Study Of Compound Phenytoin Sodium, Ephedrine Hydrochloride And Theophylline Tablets

Objective: To establish specific, sensitive and rapid liquid chromatography-tandem mass spectrometric (LC/MS/MS) methods for the determinations of multicomponent in compound preparation in human plasma at a low concentration. Methods: Phenytoin and the internal standard osalmid were extracted from plasma with liquid-liquid extraction, then separated on a Zorbax SB-C₁₈column. The mobile phase consisted of methanol-water-formic acid (90:10:0.2, v/v/v), at a flow-rate of 0.6 mL/min. A Thermo Finnigan TSQ Quantum Ultra tandem mass spectrometer equipped with an APCI interface was used as the detector and operated in the positive ion mode. Detection of the ions was performed in the SRM mode by monitoring the transitions of m/z 253 → m/z 182 for phenytoin, and m/z 230→ m/z 121 for osalmid, respectively. The linear calibration curves were obtained in the concentration range of 2.5 3000 ng/mL for phenytoin. The lower limit of quantification was 2.5 ng/mL. In the other method, human plasma samples of 0.1 mL were extracted by a single step liquid-liquid extraction procedure and analyzed using a high performance liquid chromatography electrospray tandem mass spectrometer system. The mobile phase consisted of acetonitrile-water-formic acid (55:50:0.2, v/v/v) at a flow rate of 0.5 mL/min. The analytes were eluted isocratically on a Zorbax SB-C₈ column and ionized in the positive ion mode. SRM using the precursor → product ion combination of m/z 181 → m/z 124, m/z 181 → m/z 108, m/z 195 → m/z 138 and m/z 267 → m/z 181 was used to quantify theophylline, theobromine, caffeine and the internal standard doxofylline, respectively. The calibration curves of theobromine, theophylline and caffeine were well fit over the range of 5.0 2000 ng/mL by using a weighted (1/x²) quadratic regression. The lower limit of quantification was 5 ng/mL for all the analytes. Results: Two LC/MS/MS methods were developed first time for the determination of phenytoin and the simultaneous determination of three xanthine derivate in human plasma, respectively. Conclusions: Both of the methods were successfully used in pharmacokinetics investigation of these four compounds in compound formulation.