Electroanalytical studies of antibacterial and diuretic drugs at rotating disc electrodes of gold and platinum

Abstract

A number of sulpha drugs, examples of penicillin, cephalosporin, aminoglycoside and tetracyclic antibiotics, several sulphonamide and non-sulphonamide diuretics, cephaeline, triprolidine and trimethoprim have been examined for cathodic and anodic activity at rotating disc electrodes of gold and platinum in media ranging from 1.0 mol l^–1 sulphuric acid to 0.1 mol l^–1 sodium carbonate solution. No cathodic activity at solid electrodes was observed, but all the sulpha drugs, together with benzylpenicillin, cephalexine and trimethoprim displayed anodic activity. Trimethoprim gave excellent voltammograms, Levich plots and recoveries. The voltammograms of the sulpha drugs betrayed little promise and showed evidence of strong adsorption; those of the antibiotics were yet more ill constructed. Despite non-zero intercepts in the Levich square root of frequency plots, and some misbehaviour in the concentration plots, the recoveries by rapid voltammetric determination turned out to be satisfactory, showing a mean relative standard deviation of 1.4%. Doubts are felt about the confidence to be reposed in such results. The electrode kinetic parameters, half-wave potentials, mass-and charge-transfer rate constants and charge-transfer coefficients have been determined for trimethoprim and the sulpha drugs, and the reaction mechanisms have been established. The free (protonated) amino group of the sulphas is oxidised by a one-electron reaction to the protonated radical cation imine, while trimethoprim undergoes an unusual 8-electron oxidation of the two amino groups to the dinitroso compound.