VALENCE STATE OF IRON IN THE PRESENCE OF ASCORBIC-ACID AND ETHYLENEDIAMINETETRAACETIC ACID

The valence state of iron in solutions of pH 2.6-6.0 in the presence o f ascorbic acid (AA) and ethylenediaminetetraacetic acid (EDTA) was in vestigated by reduction-oxidation titration. The results indicate that 2 mol of Fe(III) was reduced by 1 mol of AA in the pH range. The redu ction rate of Fe(III) by AA decreased drastically as the pH value incr eased. Addition of EDTA prevented Fe(III) from being reduced by AA; th at is, when a 1:1 Fe(III)-EDTA complex was formed, Fe(III) could not b e reduced by AA, at pH 2.6-6.0. Ferric iron can be reduced by AA only when the pH is below a limit, somewhere between pH 6.0 and 6.8. Above that pH limit, AA is no longer an effective reducing agent for Fe(III) . The results clarify some controversies reported in the literature an d have important implications in the formulation of iron and AA additi ves in foods and pharmaceuticals.