Extraction-spectrophotometric determination of iron as the ternary tris(1,10-phenanthroline)-iron(II)-picrate complex

Abstract

A highly sensitive extraction-spectrophotometric method has been developed for the determination of iron based on the formation of a ternary complex with 1,10-phenanthroline as a primary ligand and picrate as a counter ion. The slightly soluble red-orange complex obtained in the pH range 2–9 is easily and completely extracted into 1,2-dichloroethane. The absorbance is measured directly in the organic phase at 510 nm against a reagent blank. Beer's law is obeyed over the concentration range 0.1–3.6 µg ml^–1, corresponding to 0.01–0.36 µg ml^–1 of iron in the aqueous solution. The apparent molar absorptivity and Sandell's sensitivity were 1.3 × 10⁵ l mol^–1 cm^–1 and 0.43 ng cm^–2, respectively.

The interference of various ions was examined and the serious interferences arising from common metal ions, which are sometimes unavoidable in other methods, were not observed in the proposed method.