Spectrophotometric Determination of Sulfamethoxazole in Pure Form and its Pharmaceutical Formulation Using UV-Vis spectrophotometry

A simple and sensitive spectrophotometric method was developed for the determination of Sulfamethoxazole (SMX) in pure and pharmaceutical forms. The method is based on an oxidative coupling reaction between SMX and 2-Naphthol (2-NPH) in an alkaline medium using N-Bromosuccinimide (NBS) as an oxidant, forming a stable red-colored product with maximum absorbance at 500 nm. Reaction conditions were optimized to achieve the highest color intensity and stability. Beer’s law was obeyed in the range of 4–20 µg mL⁻¹, with a molar absorptivity of 1.22 × 10⁴ L mol⁻¹ cm⁻¹ and limits of detection and quantification of 0.1457 µg mL⁻¹ and 0.4420 µg mL⁻¹, respectively. The method showed excellent accuracy and precision (recoveries of 99–101%, RSD < 2%) and was successfully applied to Bactrim tablets without interference from excipients. This method is simple, reproducible, and suitable for routine quality control of SMX.