Extraction Equilibria and Spectrophotometric Determination of Vanadium(V) with 4-Nitrocatechol and the Ion-Pair Reagent Thiazolyl Blue Tetrazolium

The formation and liquid-liquid extraction of a yellow ternary complex of vanadium(V) with 4-nitrocatechol (NC) and the ion-pair reagent Thiazolyl Blue Tetrazolium {3-(4,5-dimethyl-2-thiazol)-2,5-diphenyltetrazolium bromide, MTT} with 1 : 2 : 3 stoichiometry (V : NC : MTT) was studied. The optimum extraction conditions (pH, concentration of the reagents, extraction time), spectrophotometric parameters of the extract and key constants (extraction constant, association constant, distribution constant) were determined. Beer's law was obeyed for concentrations ranging from 0.12 to 1.2 mu g/mL of vanadium(V) with a molar absorptivity of epsilon = 3.13 x 10(4) L/mol cm at lambda(max) = 400 nm. The effect of diverse ions was studied and extraction-spectrophotometric procedures for determination of vanadium in catalysts and steels were proposed.