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 λ_max = 415 nm was 2.8 × 10⁴ dm³ mol⁻¹ cm⁻¹, and the Beer’s law was obeyed up to 8.8 μg cm⁻³ tungsten(IV). The limit of detection and limit of quantification were calculated to be 0.27 μg cm⁻³ and 0.92 μg 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.