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 WVI 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.