Simultaneous TLC Determination of Co-trimoxazole and Impurities of Sulfanilamide and Sulfanilic Acid in Pharmaceuticals

A simple and reliable thin-layer chromatographic method for the determination of sulfamethoxazole, trimethoprim, and impurities of sulfanilamide and sulfanilic acid is developed and validated. The effect of the polarity and the composition of eluents on the separation of this mixture is investigated. A chloroform-n-heptane-ethanol (3:3:3, v/v/v) solvent system is used for a quantitative evaluation of chromatograms. The chromatographic zones, corresponding to the spots of sulfamethoxazole, trimethoprim, sulfanilamide, and sulfanilic acid on the silica gel plates, are scanned in the reflectance/absorbance mode at 260 nm. The method is found to be reproducible and convenient for the quantitative analysis and purity control of co-trimoxazole in its raw form and in its dosage forms.