A voltammetric approach to an estimate of metal release from tinplate promoted by ligands present in canned vegetables

A linear sweep voltammetric (LSV) approach is proposed for achieving rapid information on metal release from tinned containers into preserved vegetables. Chopped tomato and pea preserves were chosen as prototypes for acid and nearly neutral canned food, respectively. Metal release in these vegetables tinned into both bare and lacquered containers was compared with that found in synthetic samples containing some organic complexing agents (acetic, ascorbic, citric, malic, oxalic, pyroglutamic acids) present in the vegetables considered, thus showing that some of these components affected markedly the metal release in bare cans. These ligands were concomitantly found to also affect LSV profiles recorded in parallel at Sn and Fe electrodes in synthetic samples, causing the starting potential for their oxidation to be lower, the higher the ligand activity of the species considered. The data indicated that metal release and starting potentials for metal discharge are strictly related, so that LSV is able to provide rapid and useful information on the nature of the protective effect (electrochemical or physical) of tin on the steel underlayer, as well as on the extent of Sn and Fe release.