Simultaneous estimation of nalidixic acid and metronidazole in dosage forms using packed column supercritical fluid chromatography

Packed column supercritical fluid chromatography has been employed for the assay of nalidixic acid and metronidazole in bulk and combined dosage forms employing mebendazole as the internal standard. Supercritical fluid CO2 modified with methanol has been used as the mobile phase with elution through a JASCO (250x4.0 mm) 10 mu m ODS column with spectrophotometric detection at 320 nm. Pressure, temperature, modifier concentration and rate of flow of mobile phase have been optimised at 15.69 MPa, 40 degrees C, 9.09% (v/v) and 1.65 ml min(-1) to obtain good peak shapes and good chromatographic figures of merit. The linear dynamic ranges studied for both drugs were 10.0-60 mu g ml(-1). The validation of the method of assay of the drugs has been done by the internal standard method using mebendazole as the internal standard. The method has been extended to the assay of dosage forms in combination. (C) 1998 Elsevier Science B.V. All rights reserved.