Normal phase liquid chromatographic determination of sulfamethoxazole in tablets: collaborative study.

A stability-indicating liquid chromatographic method is presented for determining sulfamethoxazole in tablets. The method uses a 10 micron silica column, an isooctane-methylene chloride-2-propanol-acetonitrile-glacial acetic acid (70 + 25 + 5 + 5 + 0.5) mobile phase, and photometric detection at 254 nm. Seven laboratories collaboratively studied this method on powdered composite samples prepared from commercial 500 and 1000 mg tablets and on an authentic tablet mixture containing 83.32% added sulfamethoxazole. Mean assay results for the 500 and 1000 mg tablets were 102.2 and 97.9% of declared, respectively (n = 4). The mean recovery value for the synthetic sample was 99.4% (n = 4). The pooled reproducibility standard deviation (SD) (coefficient of variation (CV)) and pooled repeatability SD (CV) were +/- 1.01 (1.01%) and +/- 0.96 (0.96%), respectively. These results were in good agreement with those obtained by the Associate Referee for the titration method of USP XX. The proposed method can also be used for monitoring the presence of sulfanilamide in sulfamethoxazole by increasing the proportions of both acetonitrile and 2-propanol in the mobile phase. The method has been adopted official first action.