[Study on determination of trace copper(II) by catalytic kinetic discoloring spectrophotometry]

A kinetic spectrophotometric method for the determination of trace Cu(II) was developed in this paper. This method is based on the discoloring oxidation reaction between malachite green and hydrogen peroxide catalyzed by copper(II) in the medium of HCl solution. The influential factors of reaction and the optimum conditions for the determination of Cu2+ were investigated in detail. The decrease in absorbance was measured at 615 nm at fixed time intervals. The linear determination range is between 0 and 22 microg x L(-1) of copper(II). A detection limit of 1.92 microg x L(-1) is achieved. The catalytic and non-catalytic reactions are the first-order on copper(II), in the reaction time interval 15-20 min at 70 degrees C. The apparent activation energy of the catalytic reaction is 122.3 kJ x mol(-1). The apparent rate is 7.70 x 10(-4) s(-1). The Relative Standard Deviations (RSD) are 1.16% and the recoveries are 98.3%-100.3%. By masking Fe(III) ion with PO4(3-), the method can be applied to the determination of copper in water sample and foodstuffs with satisfactory results.