Behaviour of matrix cations (Ca2+, K+, Mg2+ and Na+) during on-line preconcentration and atomic spectrometric detection of trace metals in natural waters

A flow injection procedure with detection by inductively coupled plasma-mass spectrometry (ICP-MS) for the on-line matrix elimination and preconcentration of five elements (Cd, Co, Cu, Mn and Pb) from natural waters on a commercially available iminodiacetic acid resin is described. The results for the certified reference materials (CRMs) NASS-2 (an open ocean seawater) and SLRS-2 (a river water) gave good agreement with certified values. Recoveries from seawater were in the range 95–111% with relative standard deviations (RSDs) (n = 5) in the range 5–8%. The efficiency with which the major matrix cations (Ca2+, K+, Mg2+ and Na+) were removed has also been investigated and the importance of using suitable buffers and concentrations for the efficient removal of all of these cations with minimal reagent contamination is highlighted. The application of this column system for in-situ preconcentration is also discussed (with preconcentration factors of up to 120X) and Mn (selected as a model element) has also been quantified in SLRS-2 by flow injection-flume atomic absorption spectrometry (FI-FAAS) using 15 min preconcentration. This shows that the method can be used effectively with both flame and plasma detection.