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 analysed for the dissolved trace metals Mn, Fe, Cu and Zn using an ion chromatograph (IC) coupled directly to an inductively coupled plasma-atomic emission spectrometry (ICP-AES) system is described. Direct determination by ICP-AES of these metals in the samples was not possible since detection limits of this instrument are too high in the estuarine water matrix. The coupling of the IC to this ICP-AES system lowers detection limits sufficiently to allow analysis in two ways. First, the sample is pre-concentrated on-line; second, much of the background emission caused by the matrix is removed prior to analysis, which improves the 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 samples from the entire salinity gradient to be accurately measured against an aqueous standard calibration line. The only required pre-treatment for samples is filtration (0.2 μm) 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, Fe:1•46, Mn:0•20, Zn:0•75 μg 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 μg l−1(22, 22, 5 and 17 nM, respectively), which improved for freshwater samples. The method has a large linear range and is accurate based on analyses of standard reference material.