SPECTROPHOTOMETRIC DETERMINATION OF COPPER(II) BY USING CATALYTIC-OXIDATION OF CYSTEINE IN AN AQUEOUS N,N-DIMETHYLFORMAMIDE SOLUTION

In order to develope a new kinetic method for the determination of trace amounts of copper (II), the Cu(II)-catalyzed oxidation of such water-soluble thiols as cysteamine, L-cysteine, 2-mercaptoethanol and 2-mercaptopropionic acid has been examined in water or in a mixture of water and such aprotic solvents as N,N-dimethylformamide (DMF), dimethyl sulfoxide and acetonitrile. In this method, the decrease in the concentration of thiols was measured spectrophotometrically for the determination of Cu(II). The best sensitivity was achieved using 60% DMF solution as the reaction media and L-cysteine as water-soluble thiols. The calibration curve of Cu(II) was linear over the range 0-1.1 x 10(-6) M and passed through the origin. The determination limit was reached down to 3.9 x 10(-8) M (2.5 ppb) for Cu(II). The relative standard deviation of five successive experiments was 1.8% at 1.7 x 10(-7) M of Cu (II). The selectivity achieved by the proposed method was highly excellent, since most of diverse ions tested were tolerated high ratios. The proposed method has been applied successfully to the determination of Cu(II) in waste water.