A flow injection sensor for simultaneous determination of sulfamethoxazole and trimethoprim by using Sephadex SPC-25 for continuous on-line separation and solid phase UV transduction

A flow-through sensor based on integration of spectrophotometric detection and the different kinetics of retention/ elution of analytes on a solid support is proposed for the simultaneous determination of sulfamethoxazole (SMZ) and trimethoprim (TMP). The solid support (Sephadex SP C-25) fills both, a microcolumn placed on-line and the sensing microzone. The intrinsic absorbance of both compounds is monitored directly on the solid phase at 269 nm and so, no derivatization step is required. Using two alternate solutions, 10(-4) M hydrochloric acid and 0.20 M NaAc/HAc (pH 5.0) buffer, the sensor responds linearly in the measuring range of 50-250 and 10-70 mug ml(-1) with detection limits of 9.5 and 0.6 mug ml(-1) (500 mul of sample volume) for SMZ and TMP, respectively. The main advantages of the sensor are simplicity, rapidity and low reagents consumption. Its application to SMZ and TMP determination in synthetic samples and pharmaceutical preparations is demonstrated. The results obtained by the proposed method were compared with those obtained by a standard HPLC method. (C) 2003 Elsevier Science B.V. All rights reserved.