Successive Spectrophotometric Determination of Copper and Lead in Water Samples by Dithizone-CCl4 Extraction

Dithizone extraction spectrophotometry was applied to the successive determination of Cu(Ⅱ) and Pb(Ⅱ) in water samples. Carbon tetrachloride (CCl4) was used as extraction solvent in both cases. The extraction of Cu(Ⅱ) dithizonate was carried out in an acetate buffer medium of pH 3.8,and the absorbance of the complex in CCl4 was measured at the wavelength 551 nm. An ammoniacal buffer solution of pH 11 was added to the aqueous phase remained after extraction of Cu(Ⅱ),and appropriate amount of 1 mol·L-1 NaOH solution was added to adjust the pH of the solution to pH 9.2. Lead(Ⅱ) was then extracted as its dithizonate by CCl4 from the solution and its absorbance measured at the wavelength of 525 nm. Values of molar absorptivity of Cu-dithizonate and Pb-dithizonate in CCl4 were found to be (εCu) 6.8×104L·mol-1·cm-1 and (εPb) 1.3×105L·mol-1·cm-1 respectively. In the determination of Cu(Ⅱ) and Pb(Ⅱ) in a sample of tap water,values of RSD′s (n=6) obtained were 3.0% and 8.4% for Cu(Ⅱ) and Pb(Ⅱ) respectively.