Extractive spectrophotometric determination of tungsten(VI) using 3-hydroxy- 2-(2'-furyl)-4-oxo-4H-1-benzopyran as a complexing agent

Department of Chemistry, Kurukshetra University, Kurukshetra-136 119, India
E-mail : search@ vidya.kuk.ernet.i n; search@ granth.kuk.ernet.in    Fax : 91-1744-238277, 238628
Manuscript received 9 September 2003, revised 6 February 2004, accepted 17 March 2004

An extractive spectrophotometric method is developed for the trace determination of tungsten. Tungsten( VI) forms a light
yellow (1 : 2) complex with 3-hydroxy-2-(2' -furyl)-4-oxo-4H-1-benzopyran (HFB) in acidic medium. The coloured species is
quantitatively extracted into dichloromethanc and absorbance is measured at 405-413 nm. The method obeys Beer's law in
the range 0-2.3 µg W^VI ml^-1 with molar absorptivity and Sandell's sensitivity of 4.88 x 10⁴ dm³ mol^-1 cm^-1 and 0.0038 µg
W cm^-2, respectively, at 410 nm. The method is free from the interference of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Ta, Mo, U,
Zr, Th, Ce, Se, Re, platinum metals and many other analytically important elements. The proposed system handles
satisfactorily the analysis of several samples of varying complexity.