Speciation of Sulfamethoxazole in Pharmaceuticals via Ni(II) Complexation by Coupled CPE–LIE Techniques

A sensitive, simple, and efficient spectrophotometric method was developed for the determination of sulfamethoxazole (SMX) in pure and pharmaceutical formulations. The approach employs liquid ion exchange based on the formation of an ion-pair complex between SMX and nickel(II) ions in an acidic hydrochloric acid medium, combined with cloud point extraction (CPE) using nonionic surfactants Triton X-114 and Tween 80. Systematic optimization identified maximum absorbance wavelengths at 277 nm for Triton X-114 alone and at 291 nm for the surfactant mixture (Triton X-114 + Tween 80). Optimal extraction conditions included 0.5 M HCl, Ni²+ concentration of 100 μg mL-¹, extraction temperatures of 75°C (Triton X-114) and 80°C (surfactant mixture), and a heating duration of 15 min. Reaction kinetics evaluated via the initial rate method demonstrated rapid and efficient complex formation. The linear calibration curves ranged from 10 to 100 μg mL-¹, with limits of detection (LOD) and quantification (LOQ) of 13.3 μg mL-¹ and 40.4 μg mL-¹ (Triton X-114) and 13.4 μg mL-¹ and 40.6 μg mL-¹ (surfactant mixture), respectively. The proposed method is straightforward, reliable, and suitable for routine analysis, offering practical utility for quality control in pharmaceutical laboratories.