High Performance Liquid Chromatographic Analyses of Sulphonamides and Dihydrofolate Reductase Inhibitors. IV. Recoveries from the Stationary Phase, Quantitation and Sensitivities

Of the twenty-two sulphonamides and three commonly used dihydrofolate reductase inhibitors investigated for reverse phase separation in previous studies, the recoveries of five representative drugs from the stationary phase have been examined. Sulphanilamide, sulfisomindine, sulphaquinoxaline, diaveridine and pyrimethamine were chosen. Peak areas off the analytical column were compared with those obtained by substitution with stainless steel tubing. After careful correction for flow rate differences where necessary, 100% recoveries were indicated. As a further check, Maloprim tablets were assayed for pyrimethamine and the analysed results were found to be (99.1 ± 2.9)%. Limits of detection (LOD) for aqueous standards varied from 0.67 (for sulphanilic acid) - 0.03 μg ml/−1 (diaveridine). The linear dynamic range extended from the LOD for each drug to