Comparative LC-MS and HPLC analyses of selected antiepileptics and beta-blocking drugs.

A highly sensitive and specific assay procedure based on the combination of liquid chromatography and mass spectrometry (LC-MS) has been developed for the quantitative analysis of selected antiepileptics (carbamazepine and phenytoin) and beta-blocking drugs (acebutolol, atenolol, pindolol and propranolol) using APCI as an ionization process. The measured concentration range was 100-300 ng ml-1 for all drugs except phenytoin (0.5-1.5 micrograms ml-1). Analysis was based on direct injection of methanolic solutions of drugs into the mass spectrometer with the subsequent elution with a mobile phase consisting of methanol and 1% acetic acid solution (4:1) at a flow rate 1 ml min-1. The mass spectrometer was programmed to permit detection and determination of either fragment or molecular ions of carbamazepine, phenytoin, acebutolol, atenolol, pindolol and propranolol at m/e 194.3, 252.9, 337.2, 267.1, 249.1 and 260.1, respectively. The recorded chromatograms exhibited well-resolved peaks at retention times < 1 min. The peak area was correlated linearly to the drug concentration. Intraday precision gave relative standard deviations in the range 1.75-4.02%. Compared to HPLC, the described LC-MS was faster, more sensitive and specific. Unlike HPLC, LC-MS could be applied to analyze incompletely resolved mixtures. The absolute detection limits for LC-MS and HPLC were 0.2-0.5 and 10-25 ng, respectively. Recovery studies of the investigated compounds in pharmaceutical products using LC-MS and HPLC gave mean percentages of 97.5-102.0 and 98.4-103.3, respectively. Statistical analysis of the data using t- and F-tests showed insignificant differences between both methods for the analysis of carbamazepine, phenytoin, acebutolol and atenolol in pharmaceutical formulations. However, LC-MS gave more accurate results than HPLC for determination of pindolol in tablets. Propranolol could only be determined in tablets using LC-MS.