A simple high-performance liquid chromatographic method using ultraviolet detection was developed for the determination of metformin in human plasma. The method entailed direct injection of the plasma sample after deproteination using perchloric acid. The mobile phase comprised 0.01 M potassium dihydrogen orthophosphate (pH 3.5) and acetonitrile (60:40, v/v). Analyses were run at a flow-rate of 1.0 ml/min with the detector operating at a detection wavelength of 234 nm. The method is specific and sensitive, with a quantification limit of approximately 60 ng/ml and a detection limit of 15 ng/ml at a signal-to-noise ratio of 3:1. The mean absolute recovery value was about 97%, while the within-day and between-day coefficient of variation and percent error values of the assay method were all less than 8%. The calibration curve was linear over a concentration range of 62.5-4000 ng/ml.
A simple high-performance liquid chromatographic method using ultraviolet detection was developed for the determination of pentoxifylline in human plasma. Prior to analysis, pentoxifylline and the internal standard (chloramphenicol) were extracted from plasma sample using dichloromethane. The mobile phase comprised 0.02 M phosphoric acid adjusted to pH 4, methanol and tetrahydrofuran (55:45:1, v/v). Analysis was run at a flow-rate of 1.4 ml/min with the detector operated at a wavelength of 273 nm. The method was specific and sensitive with a detection limit of approximately 3.0 ng/ml at a signal to noise ratio of 3:1, while the limit of quantification was 12.5 ng/ml. Mean recovery value of the extraction procedure was about 99.9%, while the within-day and between-day coefficient of variation and percent error values of the assay method were all less than 10.0%. The calibration curve was linear over a concentration range of 12.5-400.0 ng/ml.