LC-MS/MS determination of carbamazepine, pindolol, and theophylline in human serum

A rapid, sensitive, and specific LC-MS/MS method for the determination of carbamazepine (CAZ), pindolol (PIND), and theophylline (THEO) in human serum is presented. The investigated drugs were separated from serum by deproteinization with acetonitrile and were analyzed on an XTerra(TM) MS, C18, 2.5 mum (2.1 mm x 30 mm) column. Carbamazepine and PIND were eluted with 65% aqueous acetonitrile containing 2 mM ammonium acetate and 0.1% formic acid, whereas THEO was eluted with 65% aqueous acetonitrile containing 2 mM ammonium acetate at flow rate 0.4 mL min(-1). The analytes were detected by a triple quadrupole mass spectrometer (Quattro LC, Micromass) using positive (CAZ, PIND) and negative (THEO) electrospray ionization modes. Multiple reaction monitoring (MRM) transitions at 237 > 194, 249 > 116, and 179 > 164 were selected for quantification of CAZ, PIND, and THEO, respectively. Calibration plots were constructed over the concentration ranges 5-50 ng mL(-1) (CAZ), 10-50 ng mL(-1) (PIND), and 501000 ng mL(-1) (THEO). The run cycle-time was similar to2 min, injection to injection. The assay procedure was highly selective, as no interference either from biological constituents or co-administered drugs was observed. Analysis of control samples of the examined drugs validated the LC-MS/MS method. The overall intra- and inter-assay %CV were in the range 0.9-5.6%, whereas the overall intra- and inter-assay %DEVs ranged -13.6/+7.4%. The protein precipitation method quantitatively recovered the analytes in mixtures from human serum samples in the range of 94.0-104.3%. The data suggest the utility of the developed LC-MS/MS for monitoring serum levels of CAZ, PIND, and THEO in clinical studies.