Fluorimetric determination of iron using 5-(4-methoxyphenylazo)-8-(4-toluenesulfonamido)quinoline

A highly sensitive and relatively interference-free fluorimetric method for the determination of iron(III) is described. The method is based on the reaction between iron(III) and 5-(4-methoxyphenylazo)-8-(4-toluenesulfonamido)quinoline in the presence of cetyltrimethylammonium bromide. The fluorescence intensity (lambda(ex) = 317 nm, lambda(em) = 534 nm) is linear up to 3 mu M (170 ng ml(-1)) iron(III) in aqueous solution with a repeatability (RSD) of 3.2% at a concentration of 180 nM (10 ng ml(-1)) and a detection limit (3s) of 2 nM (0.12 ng ml(-1)). The influence of reaction variables and the effect of interfering ions are reported. The proposed procedure was applied to the determination of trace amounts of iron(III) and total iron in tap water, canal water and wine samples without the need for preconcentration, pre-separation or organic solvent extraction.