Speciation of dissolved iron(II) and iron(III) in environmental water samples by gallic acid-modified nanometer-sized alumina micro-column separation and ICP-MS determination

A method has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in water by coupling gallic acid (GA) modified nanometer-sized alumina micro-column separation with inductively coupled plasma mass spectrometry (ICP-MS). The separation of Fe( II) and Fe( III) was achieved based on the obvious difference in reaction kinetics between Fe( II) and Fe( III) with GA. Fe( III) was selectively retained on the micro-column at pH 5.5 - 6.5, while Fe( II) could not be retained by the micro-column at the whole tested pH range of 1.0 - 6.5, and passed through the micro-column. The Fe( II) can be determined by ICP-MS directly without preconcentration/ separation procedure, while Fe( III) retained on the micro-column was then eluted with 1.0 mL of 1 mol L-1 HCl and determined by ICP-MS. The parameters affecting the separation of Fe( II) and Fe( III) were investigated systematically and the optimum separation conditions were established. Under the optimized conditions, the detection limits of 0.48 mu g L-1 and 0.24 mu g L-1 with relative standard deviation of 5.6% and 4.3% (C = 5 mu g L-1, n = 7) for Fe(II) and Fe(III) were found, respectively. No obvious effect on the speciation of Fe( II) and Fe( III) was found with the change of the ratio of Fe( II) and Fe( III) from 0 : 10 to 10 : 0. The proposed method was applied for the determination of trace Fe( II) and Fe( III) in environmental water and the recoveries for spiked samples were found to be in the range of 97 - 105%.