Spectrophotometric Determination of Copper with Violuric Acid

Copper with violuric acid at pH 9 formed a watersoluble yellow complex with absorption maximum at 343mμ, by which copper was spectrophotometrically determined. The sample solution containing 20～75μg of copper transffered to a 25ml volumetric flask. The pH was adjusted to 9 with 5ml of buffer solution (0.2 M H_3BO_3 and KCL : 0.05 M Na_2B_4O_7 1 : 4), and 5ml of 4.0×10^<-3> M violuric acid solution was added. After 15 minutes the absorbance was measured at 343mμ against reagent blank. The apparent molar absorptivity at 343mμ was 16200,and the sensitivity was 0.0040 μg Cu/cm^2. The mole ratio of copper to violuric acid was 1 : 4. Cations such as iron, cobalt, nickel, chromium and anions such as citrate, oxalate, thiosulfate, EDTA, cyanide ion interfered.