A voltammetric study of trimethoprim.

With a dropping-mercury electrode well-developed dc. polarographic reduction waves of trimethoprim (1) were obtained with 0.1 M H2SO4, citrate buffers (pH = 3--4) and acetate buffers. The solutions contain 25% ethanol as co-solvent. The reduction process is irreversible and the limiting currents are directly proportional to the concentration of I within the range from 5.10(-5) to 10(-3)M. Coulometric measurements indicate that 4 electrons are consumed per molecule. The reduction process is initiated by the reduction of the 3, 4 double bond in the pyrimidine moiety but results in the final splithing-off of two amino groups. In acetonitrile with 0.1 M LiClO4 as supporting electrolyte, two concentration-proportional anodic oxidation waves are obtained with a rotated gold disk electrode.