SELECTIVE METHOD FOR THE SPECTROPHOTOMETRIC DETERMINATION OF VANADIUMIN THE PRESENCE OF OTHER REFRACTORY ELEMENTS WITH 2,2'-IMINODIBENZOICACID

A selective method for the spectrophotometric determination of V in th e presence of other refractory elements is proposed. It is based on th e re-examination of its redox reaction with 2,2'-iminodibenzoic acid i n 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 (less than or equal to 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 nitrit e. The molar absorptivity of this system was found to be 1.2 X 10(4) 1 mol(-1) cm(-1) at 610 nm. The Lambert-Beer law is obeyed over the con centration range 0.4-2.0 mu g ml(-1) of V with the linear regression e quation A = 0.0188C-0.0229 (C = mu g of V per 25 ml) and correlation c oefficient r = 0.9990. The standard deviation (n = 10) and relative st andard deviation at the level of 20 mu g of V were found to be 0.88 mu g and 4.4%, respectively. The versatility of the proposed method was demonstrated by incorporation of the preconcentration of V with N-benz oyl-N-phenylhydroxylamine as precipitant and Mo-VI as carrier.