Oxidation of Protopine at a Pyrolytic Graphite Electrode Using Cyclic and Square-Wave Voltammetry

This paper describes oxidation of the isoquinoline alkaloid, protopine (PR) at a pyrolytic graphite electrode (PGE) using cyclic and square-wave voltammetry. In the alkaline range (pH 7.5–10.5) of a Britton–Robinson (B–R) buffer, a PR oxidation can be observed as a well-developed voltammetric peak around + 0.9 V (vs. Ag j AgCl j 3 M KCl). With increasing pH of the B–R buffer, the PR peak is shifted to less positive potentials. The acquired voltammetric data suggest that PR strongly adsorbs onto the surface of the pyrolytic graphite where it is subjected to irreversible electrochemical oxidation in its uncharged free (tricyclic) base form. The results are discussed in connection with the electrochemical oxidation of other isoquinoline alkaloids and the potential applications of these data.