ABSTRACT
Differential (ΔA), second derivative (ΔD2) and third derivative (ΔD3) differential ultraviolet spectrophotometric methods have been presented for the quantitation of niclosamide and drotaverine hydrochloride in pure forms and in their pharmaceutical formulations. For niclosamide, the method is based on measuring ΔΔ A, Δ ΔD2, A ΔD3 of niclosamide in alkaline solutions against their neutral ethanolic solutions as blanks. For drotaverine hydrochloride, the acidic solutions of the drug are measured against their alkaline solutions as blanks. The proposed methods are sensitive, highly specific and advangageous over the conventional UV assays, since the interference of the excipients, impurities, degradation products or other accompanying drugs is nullified. Accuracy of the analysis with the proposed procedures is significantly greater than the classical spectrophotometric methods.