COLUMN SOLID-PHASE EXTRACTION AS PRECONCENTRATION METHOD FOR TRACE-ELEMENT DETERMINATION IN OXALIC-ACID BY ATOMIC-ABSORPTION SPECTROMETRY AND INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

Column solid phase extraction using solid sorbent [Foam-Pap - hexamethyleneammonium hexamethylenedithiocarbamate (HMDC) immobilized on polyurethane (PU) foam mixed with methyltrioctylammonium chloride (MTOAC) immobilized on filter paper as well as the solid sorbent PU-HMDC-MTOAC mixture of the above ligands immobilized on polyurethane foam only] was applied to the preconcentration of traces of Cd, Co, Cu, Hg, Ni and Pb in analytical-reagent grade oxalic acid prior to their measurements by atomic absorption spectrometry (AAS) or inductively coupled plasma atomic emission spectrometry (ICP-AES). A disposable syringe served as a preconcentration column. Recoveries of sorption of the analytes were higher than 97%. For AAS determinations the solid chelate forming sorbents (HMDC and MTOAC) were completely dissolved in isobutyl methyl ketone (IBMK). The sorption on Foam-Pap sorbent combined with electrothermal AAS (ETAAS) allows the determination of 0.1 ng g(-1) Cd, 0.3 ng g(-1) Pb, 1 ng g(-1) Ni, 2 ng g(-1) Co and Cu, and 0.1 mu g g(-1) Hg. For ICP-AES measurements a quantitative elution was obtained with 4 mol l(-1) HNO3 for Cd, Cu, Ni and Pb, permitting the determination of 0.05 mu g g(-1) Cd, 0.1 mu g g(-1) Cu, 0.2 mu g g(-1) Ni and 1.0 mu g g(-1) Pb. The PU-HMDC-MTOAC sorbent permits the quantitative preconcentration of Cd, Cu, Fe, Hg and Pb. The combination of sorption on PU-HMDC-MTOAC sorbent with subsequent ETAAS determination allows the determination of 0.3 ng g(-1) Pb, 0.4 ng g(-1) Cd, 2 ng g(-1) Cu and Fe, and 0.1 mu g g(-1) Hg.