Short communication

Flow-through optosensor combined with photochemically induced fluorescence for simultaneous determination of binary mixtures of sulfonamides in pharmaceuticals, milk and urine

A sensitive and selective flow-through optosensor implemented with photochemically induced fluorescence (PIF) is proposed for the simultaneous determination of mixtures sulfamethoxazole/sulfanilamide and sulfathiazole/sulfanilamide. The resolution was accomplished by placing in the flow system a minicolumn filled with an appropriate solid support. Whereas one of the sulfonamides is not retained in the minicolumn and is determined by measuring its native fluorescence on the solid surface of the sensing microbeads in the detection area, the other one is retained and, after its elution, it is photochemically converted into a strongly fluorescent photoproduct which is transitorily retained on the sensing support in the flow cell and monitored. Linear calibration graphs were obtained over a concentration range of 2-3 orders of magnitude. The detection limits for the determination of sulfamethoxazole, sulfanilamide and sulfathiazole are 8.1, 2.9 and 5.7 ng mL(-1), respectively. The method was applied to pharmaceuticals, milk and human urine. The recovery of sulfamethoxazole from pharmaceuticals was 102.5% indicating no interference from trimethoprim which is not photochemically active. The recoveries for urine and milk samples fortified with sulfonamides at levels between 0.1 and 0.7 microgmL(-1) agreed within 95.0-107.5% of spiked levels.

A flow injection sensor for simultaneous determination of sulfamethoxazole and trimethoprim by using Sephadex SP C-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 microg ml(-1) with detection limits of 9.5 and 0.6 microg ml(-1) (500 microl 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.

Use of p-benzoquinone for the spectrophotometric determination of certain sulphonamides

A simple spectrophotometric method for the determination of 15 sulphonamides in bulk and in dosage forms is described. The method is based on the interaction of p-benzoquinone with sulphonamides in 0.1 M hydrochloric acid. The resulting chromophore is measured at 500 nm. The effects of different variables on colour development were established. Beer's law was obeyed in a concentration range of 10-50 micrograms ml-1. Results from the analysis of different sulphonamide tablets and ophthalmic solutions marketed locally were in good agreement with that of a reference method. Correlations between A1cm(1%) and certain physical parameters such as pKa values, characteristic volume Vx, and molecular connectivity indices 1X and 1Xv were determined by linear regression equations. A poor correlation was found between A1cm(1%) and bulkiness parameters but a highly significant negative correlation was obtained with apparent pKa values.