Four simple, sensitive and selective stability indicating spectrophotometric methods are presented for quantitative determination of the benzodiazepine drug; bromazepam (BMZ) and one of its reported potential impurities and degradation product; 2-(2-amino-5-bromobenzoyl) pyridine (ABP) in methanol. Method A, is isoabsorptive point coupled with D0 method, where good linearity was obtained by measuring the absorbance of BMZ at 264 nm (Aiso) in the concentration range of 2-25 μg mL-1, and the absorbance of ABP at its λmax 396 nm in concentration range of 0.5-24 μg mL-1. Method B, is ratio subtraction; the absorbance was measured at 233 nm for BMZ using 20 μg mL-1 of ABP, while ABP was determined directly at its λmax 396 nm using methanol as a solvent. Method C, was based on measuring the total peak amplitude of the first derivative of the ratio spectra (DD1) of BMZ from 301 to 326 nm using 10 μg mL-1 of ABP as a divisor and determination of ABP at peak amplitude of 293 nm using 5 μg mL-1 of BMZ as a divisor. In method D, ratio difference method, good linearity was achieved for determination of BMZ and ABP by measuring the differences between the amplitudes of ratio spectra at 312 nm and 274 nm and differences between the amplitudes of ratio spectra at 274 nm and 312 nm, respectively. The stability of BMZ was investigated under different ICH recommended forced degradation conditions. The suggested methods were then successfully applied for determination of BMZ in its pharmaceutical formulations.
Keywords: 2-(2-amino-5-bromobenzoyl) pyridine; Bromazepam; First derivative of ratio spectra; Isoabsorptive point; Ratio difference; Ratio subtraction.
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