A stability-indicating HPLC assay for metronidazole benzoate

A simple and rapid stability-indicating HPLC assay procedure has been developed and validated for metronidazole benzoate. The HPLC conditions were as follows, column: Waters Symmetry C8, 5 μm packing, 4.6 mm × 250 mm; detection: UV at 271 nm; injection volume: 20 μl; mobile phase: acetonitrile-0.1% glacial acetic acid in monobasic potassium phosphate (0.01 M) (40:60, v/v); isocratic elution under ambient temperature at 2.0 ml min−1. The procedure separated metronidazole benzoate and its potential degradation products, metronidazole and benzoic acid, in an overall analysis time of about 6 min with metronidazole benzoate eluting at about 5 min. The injection repeatability was 0.03%, and the intraday and interday repeatability were 0.4 and 0.7%, respectively. The procedure provided a linear response over the concentration range 0.2-800 μg ml−1 (r = 1.0000) with the limits of detection and quantitation 0.03 and 0.2 μg ml−1, respectively. The solubilities of metronidazole benzoate in water, 0.01 M hydrochloric acid and 0.05 M phosphate buffer, pH 6.8, determined each in triplicate using the procedure, were 0.2 mg ml−1 (R.S.D. 7%), 0.4 mg ml−1 (R.S.D. 2%) and 0.2 mg ml−1 (R.S.D. 8%), respectively. The results show no detectable hydrolysis of metronidazole benzoate in 0.01 M hydrochloric acid at 37 °C or in the mobile phase at ambient temperature in 10 h.