Spectrophotometric determination of tungsten(VI) using 3-hydroxy-6-methyl-2-(4'-tolyl)-4-oxo-4H-1-benzopyran

A new, simple, sensitive and selective spectrophotometric method is developed for the trace determination of tungsten. A light yellow (1: 2) complex of tungsten(VI) is formed with 3-hydroxy-6-methyl-2-(4'-tolyl)-4-oxo-4H-1-benzopyran (HMTB) in perchloric acid medium. The coloured species is extracted into chloroform and absorbance is measured at 396-402 nm. The method obeys Beer's law in the range 0-9.5 μg W VI ml ―1 , with a molar absorptivity and Sandell's sensitivity of 1.43 x 10 5 dm 3 mol ―1 cm ―1 and 0.0013 μg W VI cm ―2 , respectively at 398 nm. The method is free from the interference of a large number of elements and has been applied for the determination of tungsten in a variety of samples with satisfactory accuracy.