Determination of Sulfamethoxazole and Trimethoprim in Pharmaceuticals by Visible and UV Spectrophotometry

Amethod for the simultaneous determination of sulfamethoxazole (smx) and trimethoprim(tmp), based on a direct determination of smx after diazotization and coupling with 2naphtholby visible spectrophotometry and an indirect determination oftmp in the uv regionby difference was developed. by the suggested procedure, it was possible to analyze smxand tmp in pharmaceutical preparations without separating from each other or from theexcipients. primarily a portion of the sample was diluted to have an absorbance of 0.4-0.7at 271 nm, which corresponds to both smx and tmp. by adding sodium nitrite, hel and 2naptholto 1 ml of the diluted solution, only smx is diazotized and coupled with 2-naphtholforming a colored product with amax at 482 nm where the quantity of smx could be obtaineddirectly from a calibration curve. by plotting another calibration curve for smx at 271 nm,the influence of smx on the total absorbance of a mixture of smx and tmp at 271 nm couldbe deduced. the absorbance corresponding to tmp only was obtained by difference, whichwas transferred to quantity using a calibration curve at 271 nm. this procedure was appliedsuccessfully for the analysis of smx and tmp in pharmaceutical preparations without priorseparation and with acceptable errors.