Selective method for the spectrophotometric determination of vanadium in the presence of other refractory elements with 2,2′-iminodibenzoic acid

Abstract

A selective method for the spectrophotometric determination of V in the presence of other refractory elements is proposed. It is based on the re-examination of its redox reaction with 2,2′-iminodibenzoic acid in H₂SO₄ medium (11.1–11.4 mol l^–1) in the presence of H₃PO₄. Up to 1 mg of Ti^IV, Zr^IV, Nb^V, Mo^VI and W^VI do not interfere. V should be pre-oxidized in H₂SO₄ medium (⩽6.5 mol l^–1) at room temperature with a 0.1% m/v solution of potassium permanganate, the excess of which is removed by adding successively 1 ml of a 10% m/v solution of urea and a few drops of a 0.1% solution of sodium nitrite. The molar absorptivity of this system was found to be 1.2 × 10⁴ l mol^–1 cm^–1 at 610 nm. The Lambert–Beer law is obeyed over the concentration range 0.4–2.0 µg ml^–1 of V with the linear regression equation A= 0.0188C–0.0229 (C=µg of V per 25 ml) and correlation coefficient r= 0.9990. The standard deviation (n= 10) and relative standard deviation at the level of 20 µg of V were found to be 0.88 µg and 4.4%, respectively. The versatility of the proposed method was demonstrated by incorporation of the preconcentration of V with N-benzoyl-N-phenylhydroxylamine as precipitant and Mo^VI as carrier.