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

Abstract

A sensitive method is described for the determination of microgram amounts of iron(III) by means of its reaction at pH 9.0 with salicylate and purpurin (1,2,4-trihydroxyanthraquinone) and extraction into 4-methylpentan-2-one. The molar absorptivity of the 1:1:2 iron(III)-salicylate-purpurin complex is 4.7 × 10⁴ l mol^–1 cm^–1 at 590 nm. Beer's law is obeyed up to a concentration of 10 µg of iron in 40 ml of aqueous phase. Iron contents in salicylate, acetylsalicylate and pharmaceutical products containing these compounds can be determined at levels of the order of 10^–5%.