Extractive spectrophotometric determination of sulphonamide drugs in pure and pharmaceutical preparations through ion-pair formation with molybdenum(V) thiocyanate in acidic medium

A simple and sensitive extraction-spectrophotometric method is described for the determination of sulfonamide drugs, namely sulphamethoxazole, sulphaguanidine, sulphaquinoxaline, sulphametrole and sulphadimidine, in both pure form and in the dosage forms available in Egyptian markets. The method is based on ion-pair formation between the sulphonamides and Mo(V)-thiocyanate inorganic complex in a sulphuric acid medium followed by extraction of the coloured ion-pairs with 1,2-dichloroethane. The optimum conditions are established. The method permits the determination of sulphonamide drugs over the concentration range of 5–50 μg ml−1. The Sandell sensitivity (S), molar absorptivity, correlation coefficient and regression equations, and limits of detection (LOD) and quantification (LOQ) are calculated. The law values of standard deviation (0.09–0.38) and relative standard deviation (0.10–0.550) reflect the accuracy and precision of the proposed method. The method is applicable for the assay of the investigated drugs in different dosage forms and the results are in good agreement with those obtained by the official pharmacopeial method.