Influence of some amino acids and vitamin C on the anodic dissolution of tin in sodium chloride solution

The safety of canned foodstuffs should be evaluated not only by recognition of functional foods but also by the presence of toxicants in the human die t. In this study, the anodic dissolution of tin in 3.5% NaCl solution with and without 25-100mM glycine, serine, methionine, vitamin C and some of the ir binary mixtures was studied by means of potentiodynamic and impedance te chniques. The corroded tin surface was examined by SEM. The results indicat ed that the passive behaviour of tin is greatly improved by the presence of 50-100mM glycine and methionine while such improvement is achieved only at 100mM serine. Both cysteine and vitamin C showed aggressive action. The in fluence of the glycine/methionine mixture was found to be similar to that o f the individual components, whereas the presence of cysteine in the cystei ne/methionine mixture annuled: the inhibiting action of methionine. The imp edance results revealed that the dissolution reaction of tin in NaCl soluti on with and without glycine, serine and methionine is controlled by the cha rge transfer process while in the presence of cysteine and vitamin C, the m ixed charge transfer and diffusion control is dominant. A rough, bare tin s urface was observed in the presence of cysteine and vitamin C while a clean surface covered by corrosion products, in some zones, was observed in NaCl solution containing methionine. (C) 2001 Society of Chemical Industry.