The simultaneous speciation of aluminium and iron in a flow-injection system

It is possible to speciate Al and Fe simultaneously using complexation in a flow-injection system. Oxine is used as the reagent for Al and Fe(III), and 1,10-orthophenanthroline in combination with iodide as the reagent for Fe(II). The reaction products are extracted into chloroform. A diode array detector is used for measurement and a multivariate method, partial least squares, to separate the contributions to the signal from aluminium, iron(III) and iron(II). Results show that our system is able to measure the three components correctly in the presence of each other. The sampling frequency is 85 injections/h and the detection limit 0.06 mg/1 for all three components. Results obtained with natural water samples were satisfactory. The only cation that might possibly interfere in normal samples is Ca2+. The ‘free’ ions, Al3+, Fe3+ and Fe2+, as well as some labile complexes, such as AISO+4, are included in the measured parameter. Aluminium-fluoro complexes and large polymeric hydroxo complexes of Al and Fe(III) are excluded. Complexes with humic or fulvic acids are normally excluded, except in the case of Fe(III), for which they appear to be included to a small extent. The reduction of iron(III) to iron(II) and the oxidation of iron(II) to iron(III), in both cases mediated by humic substances, could be shown.