Spectrophotometric assay for determination of sulfamethoxazole in pharmaceutical preparations via diazotization coupling reaction with catechol


A simple, sensitive and accurate spectrophotometric method for the determination of sulfamethoxazole is developed. The method is based on diazotization reaction of sulfamethoxazole and coupling with catechol in alkaline medium to form an orange-reddish water soluble azo dye, that has a maximum absorption at 495nm. A graph of absorbance versus concentration shows that Beer law is obeyed in the range of 0.5-5ppm of sulfamethoxazole in a final volume 25ml with a molar absorptivity of 3.03x104l.mol-1.cm-1, a sandal sensitivity of 8.32x10-6μg.cm-2, a relative error of 0.18-0.78% and a relative standard deviation of 0.32-0.65%, depending on the concentration. The optimum conditions for full color development were optimized and the proposed method was applied satisfactorily to pharmaceutical preparations containing sulfamethoxazole. Statistical treatments of the obtained results was carried out using F-test and t-test, the results shows there are no significant differences between the proposed method and Bratton-Marshall method, therefore the developed method can be used as an alternative method for the determination of sulfamethoxazole in different pharmaceutical preparations.