The oxidation of Fe(III), Ni(II) and Co(II) citrates by peroxomonosulphate (PMS) in the pH range 3.0-6.0 follows autocatalysis mechanism. The acetone dicarboxylic acid (ADC), the oxidative decarboxylation product from citrate, is found to catalyze the reaction. The added metal ions switch the reaction from the ADC catalyzed decomposition of PMS to the oxidation of citrates. Based on the results from alcohol quenching, a mechanism involving oxygen atom transfer is proposed. (C) 2014 Elsevier B.V. All rights reserved.