Kinetic spectrophotometric determination of Co(II) ion by the oxidation of Ponceau 4R by hydrogen peroxide

A new, sensitive and simple kinetic method has been developed for the determination of traces of Co(II) ions based on their catalytic effect in the oxidation of trisodium-2-hydroxy-1-(4-sulphonato-1-naphthylazo)naphthalene-6,8-disulphonate (red artificial color Ponceau 4R) by hydrogen peroxide in borate buffer. The reaction was followed spectrophotometrically by tracing the oxidation product at 478.4 nm within 1 min after the imitation of the reaction. The optimum reaction conditions are: borate buffer (pH = 10.50), Ponceau 4R (8 × 10–6 mol/dm3), H2O2 (3 × 10–2 mol/dm3) at 22 oC. Following this procedure, Co(II) can be determined with a linear calibration graph up to 1.17 ng/cm3 and a detection limit of 0.20, based on the 3s criterion. The relative error ranges between 4.80–3.25 % for the concentration interval of Co(II) ions 1.76–17.61 ng/cm3. The effects of certain foreign ions the reaction rate were determined for an assessment of the selectivity of the method. The method was applied for the determination of Co(II) in pharmaceutical samples.