Electroanalytical study of salazosulfapyridine and biseptol components at the mercury electrode

The voltammetric behaviour of two sulfonamides, salazosulfapyridine (I) and sulfamethoxazol (II), and trimethoprim (III) was investigated in aqueous medium at various pH using classical and tast DC-polarography and fast scan differential pulse voltammetry (FSDPV) at a mercury dropping and a static drop electrode. Substance I, which contains an azo group, is reduced to a hydrazine derivative. The reduction of II takes place, with difficulty, by a radical mechanism. In case of III the reduction is a two- or four-electron process (depending on the acidity) that leads to the di- or tetra-hydropyrimidine derivative as a final product. The determination of these susbstances was performed using FSDPV and adsorptive stripping voltammetry (AdSV). It is dependent on the pH-value of the medium. For concentrations less than 60 ng/ml in model samples the relative standard deviations were smaller than 5% and the detection limits calculated from regression analyses were in the range 0.2–0.5 ng/ml. The determination of I–III was performed in tablets, too; the results were in accordance with data supplied by the manufacturers.