Flow injection method for iron fractionation by reaction with oxine-derivatised Fractogel

A simple and rapid flow injection analysis (FIA) method is reported for the fractionation of Fe (redox state and lability) associated with humic substances in environmental samples. The fractionation was effected on-line using a pre-concentrating microcolumn containing oxinederivatised Fractogel. Fe(II) and Fe(III) captured by the gel were subsequently eluted with 0.5M HCl. Fe(II) was quantified spectrophotometrically as the Fe(II) (1,10-phenanthroline)3 complex at pH 5.0 and total labile Fe (Fe(II)+Fe(III)) by the same method but with a downline reduction of Fe(III). The method has a 2sigma detection limit of 42nM, and a linear working range of 0.2-25µM Fe, suitable for analysis of Fe species in soil solutions and nonsaline waters. The effect of possible interferent species on the Fe(II) signal was quantified, with slight interference being observed for Cu (-13%) and Zn (-9%) when present in solution at the Fe(II) concentration (10µM). The ability of the oxine-derivatised Fractogel to sequester Fe(II) and Fe(III) bound in organic species was evaluated using both model ligands and a fulvic acid. The developed protocol was used to follow the increases in Fe(II) concentrations that occur as a result of Fe(III) photoreduction in humic water samples.