Estimation of methionine and its metal complexes by oxidation with chloramine-T and dichloramine-T

A simple method for the estimation of methionine (HMt) in aqueous solution has been developed, based on its oxidation with chloramine-T and dichloramine-T at room temperature. The direct titration, with visual or potentiometric end-point involves a two-electron change, corresponding to the formation of methionine sulphoxide. Most amino-acids do not interfere, but cysteine, glutathione and thiourea are oxidized under these conditions. A back-titration procedure in which methionine is oxidized in 0.1M sodium hydroxide by excess of chloramine-T with a four-electron change corresponding to the formation of methionine sulphone has also been developed. Methionine is oxidized to the respective nitrile, however, with excess of dichloramine-T. The methods have also been employed in estimating methionine in two of its soluble complexes, [NiMt]ClO(4) and Na[AgMt(2)].