Selective collection of inorganic iron(III) colloids in water with oxine-impregnated water-in-oil emulsion

Abstract

An oxine-impregnated emulsion was prepared by dissolving 100 mg of oxine and 0.3 ml of non-ionic surfactant (Span-80) in 10 ml of toluene and mixing with 3 ml of 1 mol l −1 hydrochloric acid by sonication (20 kHz). The water-in-oil emulsion was injected into 50 ml of water sample (containing iron(III) at the ppb level, pH 4–7) and dispersed by stirring for 10 min as numerous small globules (0.1–0.5 mm in diameter). The iron diffused through the toluene layer into the small droplets of hydrochloric acid. The emulsion was separated by flotation and heated to segregate the aqueous (hydrochloric acid) and organic (toluene) phases. The iron in the aqueous phase was determined by graphite-furnace atomic absorption spectrometry (GFAAS). Hydrated iron(III) oxide having particle sizes of larger than 1 μm did not penetrate into the emulsion. Other iron species which were not incorporated into the emulsion include humic complexes and hybrid particles of hydrated iron(III) oxide and humic substances. This discrimination can be attributed to the surfactant layer at the oil–water interfaces and gentle stirring of the solution. The conventional liquid–liquid extraction, however, did not offer such a selectivity, because all iron(III) species were simultaneously extracted into the organic phase with vigorous shaking. The unique property of the emulsion method has been applied to the separation and determination of inorganic dissolved iron species in river water.