Abstract A high-performance liquid chromatographic assay is described for establishing the completeness of electro-oxidation of a purine nucleotide drug tubercidin-5′-monophosphate (TMP) and the sequence of product formation. The assay shows that TMP was completely oxidized after ca. 2 h of electrolysis and that the product distribution continued to change after this time. The same assay was also used to show the sequence of product formation in the electro-oxidation of uric acid. Both separations were isocratic, with a 0.02 M potassium dihydrogenphosphate (pH 4.6–5.1) mobile phase.