NICKEL AND CHROMIUM IN NATURAL-WATERS - AN APPROACH FOR DETERMINATIONAT THE MU-G L-1 LEVEL BY COMBINED PRECONCENTRATION ICP-AES METHODS

The development of analytical methods for element enrichment at concen trations below the mug L-1 levels in environmental matrices is an area that still presents a great challenge. In this study, methods are des cribed that utilize the iminodiacetic acid-ethylcellulose (IDAEC) ion exchanger in combination with the inductively coupled plasma atomic em ission spectrometry (ICP-AES). Two basic methodologies for the preconc entration, both on-line by means of a flow injection analysis (FIA) co mputer-assisted system and off-line (on-column and/or batch method), a re suggested. These methods have been preliminary applied to the deter mination of Cr and Ni in natural and sea waters, where the elements ar e at the 0.1 mug L-1 level. In fresh waters, both Cr(III) and total Ni were preconcentrated by means of the on-line FIA manifold, with recov eries usually ranging from 97 to 102%. For Ni analysis in sea water, a lthough the rapid on-line procedure afforded enrichment factors of abo ut 10(2), i.e., sufficient to bring the element within the detection p ower of ICP-AES, a preliminary off-line slow step (on-column) was desi rable to remove interferents. On the other hand, Cr(III) could not be enriched from sea water using the same system. This was probably due t o the affinity of Na (present in massive amounts in sea water) for the ion exchanger. Thus, the chelation reaction between Cr(III) and resin , although time-consuming and temperature-dependent (batch method), wa s preferred. Accuracy of the procedure was verified by means of the NR CC CASS-2 Nearshore Seawater reference material.