Comparison of metal pre-concentration on immobilized Kelex-100 and quadruple inductively coupled plasma mass spectrometric detection with direct double focusing inductively coupled plasma mass spectrometric measurements for ultratrace multi-element determinations in sea-water

The extraction/pre-concentration capabilities of the liquid ion exchanger 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline (Kelex-100) immobilized on octadecyl silica have been evaluated for the analysis of trace metals in sea-water by quadruple ICP-MS (ICP-QMS) and the results are compared with those directly obtained by double focusing ICP-MS (ICP-SMS), after a simple 1 + 4 dilution of the sea-water sample. The retention capabilities of the different materials (Kelex-100 retained on Amberlite XAD-7 and Bondapack C-18 (BC-18)) were evaluated by using copper as test element and ICP-QMS for detection. Kelex-100 supported onto BC-18 provided the best performance and was evaluated, both on-line and off-line, for the pre-concentration of different trace elements present in sea-water.. Using the selected "off-line" procedure, satisfactory recoveries (95-104%) and adequate detection limits in the ng l(-1) range (V, 10; Ni, 30; Mn, 70; Cu, 170; Zn, 150: Cd, 7; Pb, 10 and U, 1 ng l(-1)) were obtained. Such multi-elemental trace metal determinations in sea-water were also attempted directly, after a simple 1 + 4 dilution of the sample and calibration with internal standards (IS) using different mass resolutions to avoid polyatomic interferences when necessary. The analytical performance characteristics and limitations of both approaches for multi-elemental determinations in coastal sea-water are compared. (C) 2001 Elsevier Science B.V. All rights reserved.