Comparative study on four spectrophotometric methods manipulating ratio spectra for the simultaneous determination of binary mixture of diflucortolone valerate and isoconazole nitrate

Four simple, accurate, reproducible and non-sophisticated spectrophotometric methods manipulating ratio spectra were developed and validated for the simultaneous determination of diflucortolone valerate (DIF) and isoconazole nitrate (ISO) without preliminary separation in pure powder form and in their cream formulation. Method A, is constant center spectrophotometric method (CC), method B is a ratio difference spectrophotometric one (RD), method C is the first derivative of the ratio spectra (1DD), while method D is the mean centering of ratio spectra (MC). Linearity correlations ranges were 5–60 μg mL−1 for DIF and 65–850 μg mL−1 for ISO. The mean percentage recoveries of DIF were 101.60 ± 1.056 for method A, 101.33 ± 0.702 for method B, 101.31 ± 1.476 for method C and 102.69 ± 1.009 for method D, respectively. For ISO were 100.59 ± 0.525 for method A, 99.68 ± 0.721 for method B, 99.67 ± 0.742 for method C and 101.37 ± 0.958 for method D, respectively. Assessment of the specificity was achieved by analyzing synthetic mixtures containing the cited drugs. The four methods were applied for the determination of the cited drugs in cream formulation and the statistical comparison of the obtained results was made with each other and with those of official methods. The comparison in pure powder form showed that there is no significant difference between the proposed methods and the official methods regarding both accuracy and precision.