Chromogenic reaction for tungsten (VI)-4-(6-bromo-2-benzothiazolylazo )pyrocatechol -emulsifier OP micellar complex and its application

In the presence of OP, a non-ionic surfactant, W ( VI ) sensitively reacts with 4-(6-bromo-2-benzothiazolylazo) pyrocatechol (6-Br-BTAPC), a new chromogenic reagent, to form a stable, negatively charged, violet-red, ternary micellar complex in the pH range of 4. 0 to 5. 2. The ratio between W ( VI ) and 6-Br-BTAPC in the complex is 1 : 2 with λ_max 558 nm, contrast (Δγ) 118 nm, apparent stability constant 3. 7×10⁹ and apparent ∈₅₅₈ 7. 34X10⁴ L · mol^-1 · cm^-1 in 20°C and pH 5. 0. Beer's law is obeyed in the range of 0 to 1. 4 mg/L of W ( VI ). The effect of many coexisting ions on the chromogenic reaction was studied. The chromogenic reaction not only has high sensitivity, but also higher selectivity. The structure of the complex was suggested. Satisfactory results have been achieved in applying this analytical method to the determination of trace or minor tungsten in alloy steel.