Specific identification test for gold

A simple and specific identification test has been worked out for gold in presence of noble metals and many common ions. It is based on a new redox reaction between gold(III) and manganese(II) in presence of diamino-cyclohexanetetraacetic acid (CDTA). At pH 5-6 gold(III) chloride in high dilutions (10 -3 M) was reduced to colloidal red-violet coloured solution of elementary gold by the addition of manganese(II)-CDTA complex. At room temperature the reaction proceeds slowly and at 40~ rapidly. The manganese(III)-CDTA formed as the oxidation product of this reaction was of ruby-red colour. The redox system is represented by the following reaction