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A rapid and simple high pressure liquid chromatography method with mass spectrometry detection was developed and validated for the determination of phenytoin in human plasma. Metaxalone was used as internal standard. The sample preparation involves a rapid and simple procedure based on liquid-liquid extraction. Analysis was performed in less than 3.0 minutes in isocratic mode on a reversed phase C18column (5μ; 50 × 4.6 mm) using a mobile phase composed of acetonitrile-buffer 2 mM ammonium acetate (80:20v/v), pH of buffer adjusted to 3.4 using formic acid, at 0.4 mL min-1 flow rate. The calibration curves were linear in the measured range between 101.2 ng mL-1and 5060.0 ng mL-1. The validated lowest limit of quantification was 101.2 ng mL-1for phenytoin. The mean relative recovery for drug and Internal standard was found to be 78.33% and 77.04%, respectively. The described method has the advantage of being rapid and easy and it could be applied in therapeutic monitoring of these drugs in human plasma.

A rapid, sensitive and specific method for quantification of metolazone in human plasma using metaxalone as internal standard is described. Sample preparation involved a simple liquid-liquid extraction procedure. The extract was analyzed by high performance liquid chromatography coupled to electrospray tandem mass spectrometry (LC–MS–MS). Chromatography was performed isocratically on a 5 μm C18analytical column (50 mm × 4.6 mmi.d.) with buffer–acetonitrile 20:80 (v/v) as mobile phase. The response to metolazone was a linear function of concentration over the range 1.00 to 2000.00 ng mL-1. The lower limit of quantification in plasma was 1.0 ng mL-1. The method was successfully applied in a bioequivalence study of a metolazone formulation after administration as a single oral dose.

A reverse phase HPLC method is described for the determination of cinitapride hydrogen tartrate in the presence of its degradation products in bulk drug. A drug was subjected to all stress conditions such as reduction, oxidation acidic and alkaline medium. Chromatography was recorded on an Intersil ODS-3 column using mixture of acetonitrile and phosphate buffer, pH adjusted to 6.7 in the ratio (70:30 v/v) as the mobile phase at the rate of 1.0 mL/min with detection at 260 nm. Glimepride was used as internal standard. The retention time of drug cinitapride was 3.8 min and glimepride an internal standard was 2.5 minute. The drug was found to degrade extensively in reduction conditions and mild degradation in the presence of in alkaline, acidic and oxidative but the drug was stable in thermal stress. The method was validated by determining its specificity, linearity, precision and accuracy. The developed method with good separation of all degradation products from drug could be successfully applied for the determination of cinitapride in the presence of its degradation products in the bulk drug. The proposed method is simple, fast, accurate and precise and hence applied for routine quality control of cinitapride in bulk drug. It can be used for analysis of samples during stability testing.