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 subst ances in environmental samples. The fractionation was effected on-line usin g a pre-concentrating microcolumn containing oxine-derivatised Fractogel. F e(II) and Fe(III) captured by the gel were subsequently eluted with 0.5 M H Cl. Fe(II) was quantified spectrophotometrically as the Fe(II) (1,10-phenan throline)(3) complex at pH 5.0 and total labile Fe (Fe(II) + Fe(III)) by th e same method but with a down-line reduction of Fe(III). The method has a 2 sigma detection limit of 42 nM, and a linear working range of 0.2-25 muM F e, suitable for analysis of Fe species in soil solutions and non-saline wat ers. The effect of possible interferent species on the Fe(II) signal was qu antified, with slight interference being observed for Cu (-13%) and Zn (-9% ) when present in solution at the Fe(II) concentration (10 muM). The abilit y 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) concent rations that occur as a result of Fe(III) photoreduction in humic water sam ples. (C) 2001 Elsevier Science B.V. All rights reserved.