Catalytic kinetic spectrophotometric determination of trace copper with copper(II)-p-acetylchlorophosphonazo-hydrogen peroxide system

Copper(II) catalyzes the oxidation of p-acetylchlorophosphonazo(CPApA) by hydrogen peroxide in 0.10 M phosphoric acid. A novel catalytic kinetic-spectrophotometric method is proposed for the determination of copper based on this principle. Copper(II) can be determined spectrophotometrically by measuring the decrease in the absorbance of CPApA at the wavelength of 554 nm using the fixed-time method. The optimum reaction conditions are as follows: H3PO4 (1.00 M) 1.0 mL, CPApA (2.19 × 10-4 M) 1.5 mL, H2O2 (4.30 × 10-2 M) 1.2 mL, reaction temperature 100 oC and reaction time 13 min. The linear range for the determination of copper(II) is 0.020-0.30 μg/mL. The limit of detection is 10.94 ng/mL. The method was satisfactorily used to determine copper in tomato and cucumber samples. The relative standard deviation of thirteen replicate determinations was 1.20-1.34% and the recovery of the method was 99.5-103.9%.