Stability indicating reversed-phase liquid chromatographic determination of metronidazole benzoate and diloxanide furoate as bulk drug and in suspension dosage form

A selective, precise and accurate isocratic RP-HPLC method has been developed and validated for the simultaneous determination of metronidazole benzoate (MB), diloxanide furoate (DF), methyl paraben (MPn) and propyl paraben (PPn) in suspension. The cis/trans isomerization phenomenon for DF has also been presented. The method uses as stationary phase a Supelco LC-18 DB (15 cm × 4.6 mm) 5 μm column and as a mobile phase a buffer-acetonitrile mixture (70:30, v/v) adjusted to pH of 2.5 at a flow rate of 2.0 mL min−1. The buffer is a 0.005 M KH2PO4 solution. The four analytes were well resolved from the degraded solutions peaks. The excepients present in the formulation do not interfere with the assay procedure. The linearity range (n = 3) is (0.20130-1.20779 mg mL−1) for MB with R of 0.99985; (0.15790-0.94740 mg mL−1) for DF with R of 0.99987; (0.01131-0.06788 mg mL−1) for MPn with R of 0.99987 and (0.00126-0.00756 mg mL−1) for PPn with R of 0.99991. Precision (n = 6) was 0.87% for MB; 1.15% for DF; 1.32% for MPn and 1.27% for PPn. The percentage recoveries (n = 3) were 99.1% for MB; 99.6% for DF; 99.1% for MPn and 98.7% for PPn. The proposed method can be utilized for the routine analysis of the four analytes in pharmaceutical dosage form.