DETERMINATION OF LEAD IN SOIL SAMPLES BY IN-VALVE SOLID-PHASE EXTRACTION FLOW-INJECTION FLAME ATOMIC-ABSORPTION SPECTROMETRY

Solid-phase extraction (SPE) using an immobilized crown ether as an ex tractant was applied to the flow injection FAAS determination of Pb-II with in-valve minicolumn preconcentration and separation, Lead(II) wa s first loaded on to a column filled with the crown ether resin from a nitric acid solution (0.8-2.0 mot dm(-3)). Among the eluents studied (oxalic acid, ammonium oxalate, citric acid, sodium citrate and tartar ic acid), 0.05 mol dm(-3) ammonium oxalate was found to be most suitab le, Calibration was made either by variation of the preconcentration t ime (using a single standard) or by using standard solutions of differ ent concentrations, The detection limit (3 sigma) was found to be 0.08 mu g of Ph and an RSD of 4.1% was achieved for 0.8 mu g of Pb-II (n = 15), An upper limit for the working range of 5 mu g of Pb-II per samp le was found, Interferences of cationic and anionic sample components were found to be negligible. Application to the determination of Pb-II in digested soil samples is described and the method was validated by using certified reference materials.