ION CHROMATOGRAPHY-INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY (IC-ICP-AES) AS A METHOD FOR DETERMINING TRACE-METALS IN ESTUARINE WATER

A method by which estuarine water samples have been successfully analy sed for the dissolved trace metals Mn, Fe, Cu and Zn using an ion chro matograph (IC) coupled directly to an inductively coupled plasma-atomi c emission spectrometry (ICP-AES) system is described. Direct determin ation by ICP-AES of these metals in the samples was not possible since detection limits of this instrument are too high in the estuarine wat er matrix. The coupling of the IC to this ICP-AES system lowers detect ion limits sufficiently to allow analysis in two ways. First, the samp le is pre-concentrated on-line; second, much of the background emissio n caused by the matrix is removed prior to analysis, which improves th e signal-to-noise ratio, This latter feature of the method is shown to remove observable matrix effects from sample analysis, precluding the need for the use of the method of standard additions, and allowing sa mples from the entire salinity gradient to be accurately measured agai nst an aqueous standard calibration line. The only required pre-treatm ent for samples is filtration (0.2 mu m) and buffering to pH 5.4 with ammonium acetate; multi-elemental analysis is complete within 10 min. For the metals determined, the limits of determination were Cu:1.11, F e:1.46, Mn:0.20, Zn:0.75 mu g l(-1) (17, 26, 4 and 11 nM, respectively ). Precision on saline samples was estimated at Cu:1.41, Fe:1.23, Mn:0 .27, Zn:1.11 mu g l(-1) (22, 22, 5 and 17 nM, respectively), which imp roved for freshwater samples. The method has a large linear range and is accurate based on analyses of standard reference material.