Application of a ternary complex of tungsten(VI) with 4-nitrocatechol and thiazolyl blue for extraction-spectrophotometric determination of tungsten

A new ternary ion-association complex of tungsten(VI), 4-nitrocatechol (NC), and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (Thiazolyl Blue, MTT) was obtained and studied using an extraction-spectrophotometric method. The optimum pH, reagent concentrations, and extraction time were determined. The composition of the complex was found to be W(VI) : NC : MTT = 1 : 2 : 2. The extraction process was investigated quantitatively and the key constants were calculated. The molar absorptivity of the chloroform extract at lambda(max) = 415 nm was 2.8 X 10(4) dm(3) mol(-1) cm(-1), and the Beer's law was obeyed up to 8.8 mu g cm(-3) tungsten(IV). The limit of detection and limit of quantification were calculated to be 0.27 mu g cm(-3) and 0.92 mu g cm(-3), respectively. The effect of foreign ions and reagents was studied and a competitive method for determination of tungsten in products from ferrous metallurgy was developed. The residual standard deviation and the relative error were 0.53 % and 0.2 %, respectively.