Solid-liquid separation after liquid-liquid extraction: spectrophotometric determination of iron(II) by extraction of its ternary complex with 2,2′-dipyridyl and tetraphenylborate into molten naphthalene

Abstract

A method for the spectrophotometric determination of iron(II) after extraction of its ternary complex with 2,2′-dipyridyl and tetraphenylborate into molten naphthalene has been developed. Iron(II) reacts with 2,2′-dipyridyl to form a water-soluble coloured complex. This complex cation forms a water-insoluble stable ternary complex in the presence of sodium tetraphenylborate, which is easily extracted into molten naphthalene in the pH range 2.8–7.6 by vigorous shaking for a few seconds. The solid naphthalene containing the iron 2,2′-dipyridyl tetraphenylborate complex is separated by filtration and dissolved in acetonitrile. The absorbance is measured at 521 nm against a reagent blank. Beer's law is obeyed in the concentration range 2.2–65.5 µg of iron in 10 ml of acetonitrile solution. The molar absorptivity and Sandell's sensitivity are 8.89 × 10³ l mol^–1 cm^–1 and 0.006 3 µg cm^–2 at 521 nm, respectively. The interference of various ions has been studied in detail. The method has been applied to the determination of iron in standard metallic samples and the results are compared with those obtained by the 1,10-phenanthroline method.