Spectrophotometric determination of trace amounts of iron(III) in oxalates by extraction of the mixed-ligand iron-oxalate-purpurin complex

Abstract

A sensitive method is described for the determination of microgram amounts of iron(III) by means of its reaction at pH 8.5 with oxalate and purpurin (1,2,4-trihydroxyanthraquinone) and extraction into 4-methylpentan-2-one. The molar absorptivity of the 1 : 1 : 2 iron(III)-oxalate-purpurin complex is 5.7 × 10³ m² mol^–1 at 600 nm. Beer's law is obeyed from 0.05 to 0.20 p.p.m. of iron in the aqueous phase. Iron contents in oxalates of the order of 10^–4% can still be determined with certainly by means of this method.