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Determination of iron species in natural waters by ICP-AES

The determination of the oxidation states and other species containing iron is of considerable interest in both atmospheric chemistry and oceanographic research. It has recently been suggested that iron may be the limiting factor for primary bilogical productivity in the open oceans. Fe(II) is probably the preferred nutritient for phytoplankton. In clouds, fog rainwater the photoreduction of Fe(III) to Fe(II) has also been proposed as a major source of aqueous hydroyxl radical which is a key radical in atmospheric photochemistry. In addition Fe(III) complexes have been shown to be effective catlysts for the heterogeneous autoxidation of SO2 in coluds. The redox cycling of (Fe(II) and Fe(III) has significant effects on the other redox processes in many natural water systems. A great number of investigations of the iron presence in atmospheric water has been limited to the determination of its total dissolved amount, and relatively little is known about its oxidation state. Most of the analytical techniques proposed for the total iron determination are quick and selective but they lack in sensitivity at low concentration levels. Preconcentration and separation are usully required prior to analysis [1]. The determination of the oxidation states of iron in natural water systems has been generally achieved by complexation with specific chelating reagents follwed by spectrophotometric measurments or by voltametry. Both techniques suffer from interferences caused by the presence of the variety of Fe(III) oxides or different ligands present in real samples [2-4]. Iron species in natural waters can be preconcentrated and separated on an ion chromatographic column. Significant improvement in speciation has been by coupling of chromatography with an element-specific detectors like ICP-AES. Problems that occur in real sample analysis are mainly due to instability of some iron species and for this reason sample preparation and storage do considerably effect the results. If the sample preparation step is influenced by acidifying the results depend on the amount of acid added [5]. In this work iron species were separated as anionic complexes with PDCA (pyridine-2,6-dicarboxylic acid) using a Dionex HPIC-CS5 column. The ion chromatograph was connected by a PTFE tubing directly to the nebulizing system of the ICP spectrometer. The analog signal of the phototube was registrred directly by a digital voltmeter (sampling frequency 2Hz). Samples of natural water were analysed after preconcentration on a HPIC-CS5 guard column. The most prominet iron emission line of 259.925nm was used for all measurments of the iron species and for determination of the detection limits. Coupling of IC with ICP-AES is a powerful tool for the on-line preconcentration, separation and detection of Fe(II) in water matrices. [1] Pehkonen, S., Analyst. 1995, 120, 2655. [2] Kolotyrkin, I.Y. Shpigun, L.K., Zolotov, Y. A., Malahoff, A., Analyst, 1995, 120, 201. [3] King, D. W., Lin, J., Kester, D. R., Anal. Chim. Acta, 1991, 247, 125. [4] Hirayama, K., Unohara, N., Anal. Chem., 1988, 60, 2573. [5] Urasa, I. T., Mavura, W. J., Intern. J. Environ. Anal. Chem., 1992, 48, 229.

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