Kinetic determination of trace amounts of Cu(II) in water based on its catalytic effect on the reaction of mercaptosuccinic acid and Cr(VI)

A kinetic method is presented for the determination of Cu(II) in water. It is based on the catalytic effect of Cu(II) on the oxidation of mercaptosuccinic acid by chromate in acidic media. The extent of the reaction is followed spectrophotometrically at 345 nm and pseudo-first order rate coefficients are determined as a function of catalyst concentration. The optimum operating conditions regarding ionic strength, temperature and concentration of reagents were established. Interference by several ionic species was studied and the effects of Fe(III) and Pb(II) were suppressed by complexation with pyrophosphate. Calibration lines were obtained for both low (30-640 mug . 1(-1)) and high (640-1500 mug . 1(-1)) catalyst concentrations. The relative standard deviation for 625 mug . 1(-1) Cu(II) is 6.1% (n = 5). The detection limit is 22 mug . 1(-1). The method was applied to real samples of river water of the mining region of Baia-Mare, Northern Romania. The results were compared to those obtained by an officially standardized AAS method. Good agreement was attained. The method is inexpensive, fairly rapid and sensitive. Moreover, its working range covers the exact range of concentrations usually encountered in the mentioned geographic area.