Catalytic spectrophotometric determination of tungsten using the malachite green–Ti(III) redox reaction and a thiocyanate activator

Thiocyanate was found to have a highly activating effect on the tungsten-catalyzed reaction of malachite green with Ti(III). A highly sensitive, selective and simple method was developed for the determination of tungsten based on this effect. The reaction rate was monitored spectrophotometrically by measuring the change in absorbance at 616 nm using a fixed time method. The effect of different parameters was studied and optimum conditions were established. The calibration graph was linear in the range of 1.2–10 and 10–80 ng ml−1. The detection limit was 0.15 ng ml−1 and relative standard deviation for ten replicate measurements of 1.2 ng ml−1 of tungsten was 1.8%. The proposed method was applied successfully for the determination of tungsten in hot spring waters.