Catalytic Spectrophotometric Determination of Ultra Trace-level Copper(II) with Indigo Carmine

In this paper, a novel kinetic spectrophotometric method for the determination of ultra trace Cu(II) was developed. This method was based on catalytic action of Cu(II) on the oxidation of indigo carmine by ammonium persulfate in Na2B4O7-HCl buffer solution (pH = 9.09) and in presence of the surfactant-TritonX-100. Effects of some factors on the reaction speed were investigated in this study. It was observed that the concentration of Cu(II) was linearly correlating to Delta A in the range of 2.0 x 10(-10)-1.6 x 10(-9) g/mL for Cu(II) in this method. The detecting limit of the proposed method was 1.8 x 10(-11) g/mL. This system was a first-order reaction for Cu(II). The apparent rate constant was 3.19 x 10(-4) s(-1) and the apparent activation energy was 112.5 kJ/mol in this system. Most of the foreign ions did not interfere with the determination and the interferences of Fe(III) and Al(III) could be masked by F-. The proposed method was applied to the determination of ultra trace-level copper(II) in real samples with satisfactory results.