Spectrophotometric assays of diloxanide furoate and tinidazole in combined dosage forms

Two spectrophotometric methods have been developed for the simultaneous determination of diloxanide furoate and tinidazole in combined dosage formulations without prior separation. The first method is based on the measurement of the absorbance of a methanolic solution of the sample at 259 and 311 nm and application of a simplified Vierordt equation for the determination of diloxanide furoate, whereas tinidazole is determined by direct spectrophotometry. The second method is a difference spectrophotometric procedure based on measurement of the absorbance of the sample solution in water relative to that of an acidic or alkaline solution of identical concentration at the appropriate wavelength of maximum difference absorption. The results are calculated by reference to standard absorptivity values.