DETERMINATION OF TRACE-METALS IN NILE RIVER AND GROUND-WATER BY DIFFERENTIAL-PULSE STRIPPING VOLTAMMETRY

The determination of trace metals in river water and ground water by DPSV is seriously disturbed by the presence of organic complexes. The influence of these substances can be eliminated by acidification of the samples with acids. Cd, Pb and Cu were determined at pH 1.1 (HNO3 medium) and Zn, Cd, Pb and Cu at pH 2 (HCl medium), in both the Nile river and ground water. Zn was determined at pH 3.5 in HCl and pH 4.5 in HNO3, after neutralizing the samples with NH3/NH4Cl buffer. Manganese could then be determined, after further addition of ammoniacal buffer solution up to pH 7.5 and 8.5. Ni and Co were determined in the adsorptive mode after formation of dimethylglyoximates at pH 9.2. The effect of pH on the stripping peaks of manganese was studied. Good agreement was observed between DPSV and AAS results for Zn, Cd, Pb, Cu and Mn, but the concentrations of Ni and Co were below the detection limits for AAS. Good agreement was obtained between DPSV results in HCI and HNO3 for Ni and Co. The results indicate that decomposition of organic complexes by acidification with HNO3 is better than in the case with HCl for Zn, Pb, Cu, Ni and Co, but HCl is better than HNO3 for Cd and Mn.