Development and application of a sensitive and rapid analytical method to determine the rare-earth elements in surface waters

Abstract

A new cost-effective method to determine the 14 rare-earth elements (REE's) in waters to levels as low as 0.2–1.0 ng l −1 (ppt) has been established. Inductively coupled plasma mass spectrometry (ICP-MS) is used for measurement following automated preconcentration using the Dionex® MetPac CC-1 resin of iminodiacetate functionality. The free REE ion is chelated onto the resin while alkali and alkaline-earth elements are washed through and separated, enabling the method to be applied to seawater as well as fresh water. The eluant, 0.8 M HNO 3, provides an ideal medium for analysis by ICP-MS and the suite of elements determined can be expanded to include first-row transition elements, Cd, Pb and U. Based on replicate analyses of control samples and data for field and laboratory duplicate samples (lakes and streams), relative standard deviations are better than ±10% except where concentrations are below 5 ng l −1. Application of this method to 135 lake waters in the Baie d'Espoir region of Newfoundland indicates: (a) contamination is not introduced from sampling bottles (Nalgene®, LPE) or during the filtering and acidification process, even at low ng l −1 levels; (b) there is a high degree of correlation in element distribution patterns between lake waters and their corresponding centre-lake sediments for Yb and Tb; (c) the chondrite-normalized plots for water and sediment are similar in shape and show consistent patterns within geological units but are distinct between such units; and (d) the powerful potential of REE concentrations in surface water for geochemical mapping.