Spectrophotometric methods are proposed for the determination of drugs containing a phenol group [salbutamol sulphate (SLB), ritodrine hydrochloride (RTD), isoxsuprine hydrochloride (IXP)] and drugs containing an aromatic amine group [dapsone hydrochloride (DAP), sulfamethoxazole (SFM), and sulfadiazine (SFD)] in pharmaceutical dosage forms. The methods are based on coupling of N, N-diethyl-p-phenylenediamine sulphate with the drugs in the presence of KIO4 to give a green colored product (λmax at 670 nm) and a red colored product (λmax at 550 nm), respectively. Linear relationships with good correlation coefficients (0.9986-0.9996) were found between absorbance and the corresponding concentration of drugs in the range 1-7, 2-22, 1-17, 1.5-12, 2-25, and 2-21 μg mL-1 for SLB, RTD, IXP, DAP, SFM and SFD, respectively. Variable parameters such as temperature, reaction time and concentration of the reactants have been analyzed and optimized. The RSD of intra-day and inter-day studies was in the range of 0.2-1.0 and 0.4-1.0%, respectively. No interference was observed from common pharmaceutical adjuvants. The reliability and performance of the proposed methods was validated statistically; the percentage recovery ranged from 99.5 ± 0.1 to 99.9 ± 0.3%. Limits of detection were 0.14, 0.21, 0.51, 0.44, 0.33 and 0.37 μg mL-1 for SLB, RTD, IXP, DAP, SFM, and SFD, respectively.
