DETERMINATION OF TOTAL METALS IN SEWAGE SLUDGES BY ION CHROMATOGRAPHY

An accurate and precise ion chromatographic (IC) method for determination of total Cu, Mn, Ni, Pb, and Zn was developed. The method consists of three steps: (i) digestion of the soil sample by using HNO3, HClO4, and HF; (ii) extraction of the metals by using dithizone in CHCl3; and (iii) destruction of the metal-dithizonate complex with HNO3 and determination of the metals by IC. The IC system consisted of a guard (HPIC-CG5) column and separator (HPlC-CS5) column followed by postcolumn reaction with 4-(2-pyridylazo) resorcinol (PAR) to form colored metal complexes. The absorbance of the metal-PAR complexes was measured by a UV-VIS detector at 520 nm. Two different eluents were required for separation of these metals. Simultaneous determination of Cd, Cu, Mn, and Zn was achieved by using an eluent containing 4 mM 2, 6-pyridinedicarboxylic acid and 50 mM HOAc-NaOAc buffer (pH 4.8). Simultaneous determination of Cu, Ni, Pb, and Zn was accomplished by using an eluent containing 40 mM oxalic acid and 50 mM HOAc-LiOAc buffer (pH 4.8). Results by the IC method for determination of total Cu, Mn, Ni, Pb, and Zn in several diverse sewage sludges were in good agreement with those obtained by atomic absorption spectrophotometry (AA). Results also showed that the proposed IC method is precise and has the same degree of precision as that of AA. Also, the sensitivity and detection limits of IC for these metals are similar to those of flame AA.