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

Nivedita Agnihotri*, Navneet Kaur, Rajesh Agnihotri

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6-Chloro-3-hydroxy-7-methyl-2-(2’-thienyl)-4-oxo-4H-1-benzopyran, Determination, Extraction, Spectrophotometry, Tungsten


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.