Analytical Chemistry of Tungsten: Method of Trace Determination of Tungsten (VI) Using 6- Chloro-3-hydroxy-7-methyl-2-(2’-thienyl)-4-oxo- 4H-1-benzopyran as an Analytical Reagent

Abstract

A binary complex of tungsten (VI) with 6-chloro-3-hydroxy-7-methyl-2-(2’-
thienyl)-4-oxo-4H-1-benzopyran (CHMTB) is produced from hydrochloric acid medium
and studied spectrophotometrically. The 1:3 (M: L) complex is quantitatively extracted into
dichloromethane and absorbs light intensity in the range 410-418 nm. Beer’s law as shown
by the calibration curve holds good in the W(VI) concentration range of 0-1.6 μg ml-1 in the
measured solution (r = 0.9998). The molar annihilation coefficient and Sandell’s sensitivity
are calculated to be 9.93 × 104l mol-1 cm-1 and 0.00185 μg cm-2, respectively at 415 nm. The
proposed method offers advantage of a quick, cheap, reproducible, sensitive and selective
technique and has been successfully used in the determination of tungsten in spiked
samples like flue dust and water with satisfactory results.