Determination of bifonazole in creams containing methyl- and propyl p-hydroxybenzoate by derivative spectrophotometric method.

A second order derivative spectrophotometric method for the determination of bifonazole in the presence of methyl- and propyl p-hydroxybenzoate as preservatives has been developed. The determination was performed in a 0.1 M HCl solution at 241.5 nm, a wavelength corresponding to the intersection of the second order derivative spectra (2D) of methyl- and propyl p-hydroxybenzoate with the axis (zero-crossing point). On the basis of the knowledge of acidity constants and solubility, as well as of the investigations of zero-order and 2D spectra of bifonazole and preservatives, these conditions were chosen as optimal ones. A calibration curve constructed for bifonazole concentrations ranging from 1.5 to 15 microg/ml had a correlation coefficient of 0.9998. Reliability and reproducibility of the method was checked by analyzing laboratory mixtures of bifonazole and preservatives (recovery 99.97-102.7%; RDS 0.48-1.46%). The proposed method was applied for the determination of bifonazole in a commercial cream formulation. The mean value of bifonazole obtained per 100 g cream was 1.029 g (102.9% of the labeled claim) with a RSD of 0.60%.