Spectrophotometric determination of iron(III) with 8-quinolinol in the presence of nonionic surfactant and sodium thiosulfate.

Abstract

Iron(III) formed a water soluble complex with 8-quinolinol in the presence of Triton X-100 and sodium thiosulfate at pH 4.4, showing two absorption maxima at 460 nm and 580 nm. Sodium thiosulfate was added as a masking agent of copper(II). Recommended procedure is as follows : Take a sample solution containing up to 500μg of iron(III) and adjust pH to 3.43.5 with 0.25 mol dm-3 sodium acetate solution. Add 0.2 cm3 of copper(II) sulfate solution(Cu 10 mg cm-3), 2 cm3 of Triton X-100 solution(0.12 g cm-3), 3 cm3 of 1 mol dm-3 sodium thiosulfate solution, and 2.0 cm3 of 8-quinolinol solution(8 mg cm-3). Copper sulfate solution was added to favor the formation of iron-8-quinolinolate complex. Adjust the pH to 4.4 with 0.25 mol dm-3 sodium acetate solution and dilute to 25.0 cm3 with water. After allowing to stand for 20 min, measure the absorbance at 460 nm or 580 nm against a reagent blank. Beer's law is valid over the range of 2200 ppm of iron(III). The apparent molar absorptivities at 460 and 580 nm are 5.17 × 103 and 3.91 × 103 dm3 mol-1 cm-1, respectively. Up to 10 mg of Cu(II), 4 mg of Cd(II), Mn(II), Pb(II), 1 mg of Cr(III), Mo(VI), 0.4 mg of Ni(II), 0.2 mg of Zn(II), Al(III), and 0.1 mg of Co(II), Ti(IV), and V(V) do not interfere. Interference of Cu(II) 10100 mg is removed by coprecipitation of iron(III) with manganese (IV) hydroxide from its ammoniacal solution containing hydrogen peroxide.