Abstract
An analytical method for multielement determination of tarce elements in natural water (terrestrial water and seawater) by ICP-AES (inductively coupled plasmaatomic emission spectrometry) and ICP-MS (inductively coupled plasma massspectrometry) has been explored with the aid of chelating resin preconcentration, using Chelex-100 resin from Bio-Rad Laboratories (USA) . In order to evaluate the analytical reliability, the present chelating resin preconcentration/ analytical plasma spectrometry (ICP-AES and ICP-MS) method was applied to the determination of trace elements in river water certified reference material issued from the Japan Society for Analytical Chemistry and coastal seawater certified reference materialissued from National Research Council of Canada. The present method was alsoapplied to the analyses of Lake Biwa and Kagamiga-ike pond water samples. Furthermore, chemical speciation of trace elements in natural water by a combined system of SEC (size exclusion chromatography) / UV absorption/ ICP-MS (or ICP-AES) wasperformed after ultrafiltration preconcentration to elucidate the dissolved states or species of such trace elements. In ultrafiltration preconcentration, an ultrafiltrationfilter with the molecular permeation limit of 10, 000 Da in molecular weight (MW) wasused. As a result, it has been elucidated that most of trace elements exist as the largeorganic molecule-metal complexes (LOMMCs) in natual water. Such LOMMCs areobserved at Peak 1 (MW > 300, 000 Da) and Peak 2 (MW 10, 000-50, 000 Da) on the SEC chromatogram detected by ICP-MS. The fractional distributions of trace elements in the small-molecule, large-molecule and particle fractions of seawater werealso evaluated from the determination of trace elements in membrane (pore size 0.45, um) -filtered seawater, ultrafiltration (molecular permeation limit 10, 000 Da) -filteredseawater and particles remained on the membrane filter. In consequence, it wasconfirmed that LOMMCs of trace metals exist even in seawater. From these experimentalresults, a string-ball model is proposed as the dissolved species in naturalwater. The string-ball model is a formation model of LOMMCs with MW larger than 300, 000 Da, corresponding to Peak 1 in the SEC chromatogram, in which LOMMCs arecomposed of hydroxide colloides of Al and Fe as the cores and biogenic organicmaterials and diverse inorganic metal ions as the adsorbents on the cores, and such LOMMCs may grow their sizes to form the suspended particles in natural water. Onthe other hand, LOMMCs corresponding to Peak 2 in the SEC chromatogram may bemetal complexes of trace elements with biogenic protein-like compounds.
