The use of BF(-)(4) as the supporting electrolyte anion in voltammetric studies on carbon electrodes-a cautionary note

BF(-)(4), a supporting electrolyte anion commonly employed in aprotic as well as protic solvents, is found to give an anodic peak at around +0.8 V vs. SCE on glassy carbon electrodes in dimethylformamide media. The voltammetric peak is influenced by the sweep-rate as well as the concentration of BF(-)(4). The electrode, when anodically polarized under these conditions, is also found to retard the charge-transfer rate of the ferricyanide/ferrocyanide redox system. Possible mechanisms for formation of a film on the electrode are discussed; possibilities are fluorination of carbon atoms on the electrode surface by reactions such as C(lattice) + BF(-)(4) --> (CF ... BF(3))(lattice) + e(-) or CH(lattice) + BF(-)(4) --> (CF ... BF(3))(lattice) + H(+) + 2e-. The analytical importance of considering the influence of BF(-)(4) and other fluoride species on carbon electrodes in the anodic region is emphasized.