Improved selectivity in detection of polar basic drugs by liquid chromatography-electrospray ionization mass spectrometry. Illustration using an assay method for the determination of famotidine in human plasma.

It is well to assume that bioanalytical chromatographic methods for the determination of polar basic drugs are developed and optimised according to a standardised procedure which involves two alternatives: (a) modifications in the sample preparation procedures, and (b) changes in the stationary phase of the chromatographic system. In this paper, a simple and rapid chromatographic procedure using a specific analytical detection method (ESI tandem mass spectrophotometric detection) in combination with a fast and efficient sample work-up procedure, protein precipitation, is presented. A demonstration of the entire chromatographic procedure is given for an HPLC method for the determination of famotidine in human plasma, a basic polar drug with poor solubility in organic solvents. In order to optimize the mass detection of famotidine, several parameters such as ionization mode, fragmentor voltage, m/z ratios of ions monitored, type of organic modifier and eluent additive, were investigated. Each analysis required 5 min. The calibration curve of famotidine in the range 1-200 ng/ml was linear with a correlation coefficient of 0.9992 (n = 6), and a detection limit a signal-to-noise ratio of 3 was approximately 0.2 ng/ml. The within- and between-day variations in the famotidine analysis were 5.2 (n = 6) and 6.7% (n = 18), respectively. The applicability of this method was also demonstrated for the analysis of plasma samples in a Phase-I human pharmacokinetic study.

A sensitive method for the determination of gemfibrozil in human plasma samples by RP-LC.

A sensitive high-performance liquid chromatographic assay for the quantitative determination of gemfibrozil is described in this work. Ibuprofen was used as internal standard. The assay involved a single cyclohexane extraction and LC analysis with fluorescence detection. Chromatography was performed at 40 degrees C on a Hypersil ODS column. The mobile phase was a mixture of a solution of phosphoric acid 0.4% and acetonitrile (45:55). The method was validated. The detection limit of this method was 0.025 microg ml(-1); only 0.5 ml of the plasma sample was required for the determination. The calibration graph was linear from 0.05 to 0.5 microg ml(-1) and required a cubic equation from 0.5 to 30 microg ml(-1). Intra and inter-day precision (C.V.) did no exceed 15%. Mean recoveries were of 90.15+/-6.9% (C.V.'s<8%) for gemfibrozil and 93.10% for ibuprofen Applicability of the method was demonstrated by a pharmacokinetic study in normal volunteers who received gemfibrozil by oral route.

Rapid liquid chromatographic assay for the determination of acetaminophen in plasma after propacetamol administration: application to pharmacokinetic studies.

A simple method for the rapid estimation of acetaminophen in plasma is described here. p-Propionamidophenol was used as internal standard. The assay involved a single ethyl acetate extraction and liquid chromatographic analysis at a wavelength of 242 nm using a reversed-phase encapped column, with a mobile phase of acetonitrile and 0.005 M potassium dihydrogen phosphate adjusted at pH 3.00. The limit of quantitation of acetaminophen by this method was 0.05 microg ml(-1), only 0.1 ml of the plasma sample was required for the determination. The calibration graph was linear from 0.05 to 100 microg ml(-1). Intra and inter-day precision (CV) did not exceed 8.93%. Mean recoveries of 90.31% with a CV of 1.38% were obtained. Applicability of the method was demonstrated by a pharmacokinetic study in normal volunteers who received 2 mg propacetamol.