Ion chromatographic preconcentration of Cu and Cd from ultra-high-purity water and determination by electrothermal atomic absorption spectrometry

A method based on preconcentration of Cu and Cd from ultra-high-purity wate r by ion chromatography (IC) and determination by electrothermal atomic abs orption spectrometry is described. A small low-capacity ion-exchange concen trator Dionex HPIC-CG5 and mobile phase of 3 mM pyridine-2,6-dicarboxylic a cid (PDCA) are used. Water samples are loaded onto the preconcentration col umn at a flow-rate ranging from 1 to 3.5 mi min(-1). Large sample volumes ( up to 200 mi) can be loaded onto the concentrator without losing metal ions . Elution is carried out in the reverse direction of sample loading and the volumes of effluent are as small as 0.150 and 0.200 mi for copper and cadm ium, respectively. Under these conditions the preconcentrated ions coelute. The detection limits, based on the Hubaux-Vos method, for Cu using a 1300- fold preconcentration in the IC step was found to be 1 pg ml(-1), and was l imited due to impurity in PDCA, while the detection limit found for Cd usin g a 1000-fold preconcentration was 0.02 pg ml(-1). Ultra-high-purity water produced by a Millipore system is successfully analysed by the proposed met hod and the content of Cu and Cd are found to lie in the range 1-10 pg ml(- 1). (C) 2001 Elsevier Science B.V. All rights reserved.