Simultaneous determination of clozapine, olanzapine, risperidone and quetiapine in plasma by high-performance liquid chromatography–electrospray ionization mass spectrometry

Clozapine (CLZ), olanzapine (OLZ), risperidone (RIP) and quetiapine (QTP) have been widely used in the treatment of schizophrenia. However, no study (or little study) has been conducted to determine the four drugs simultaneously by the use of high-performance liquid chromatography–electrospray ionization mass spectrometry (HPLC–MS/ESI). Objective: To develop a sensitive method for simultaneous determination of CLZ, OLZ, RIP and QTP in human plasma by HPLC–MS/ESI. Methods: The analytes were extracted twice by ether after samples had been alkalinized. The HPLC separation of the analytes was performed on a MACHEREY-NAGEL C 18 ( 2.0 mm×125 mm, 3 μm, Germany) column, using water (formic acid: 2.70 mmol/l, ammonium acetate: 10 mmol/l)–acetonitrile (53:47) as mobile phase, with a flow-rate of 0.16 ml/min. The compounds were ionized in the electrospray ionization (ESI) ion source of the mass spectrometer and were detected in the selected ion recording (SIR) mode. Results: The calibration curves were linear in the ranges of 20–1000 ng/ml for CLZ and QTP, 1–50 ng/ml for OLZ and RIP, respectively. The average extraction recoveries for all the four analysts were at least above 80%. The methodology recoveries were higher than 91% for the analysts. The intra- and inter-day R.S.D. were less than 15%. Conclusion: The method is accurate, sensitive and simple for routine therapeutic drug monitoring (TDM) and for the study of the pharmacokinetics of the four drugs.