Spectrophotometric determination of tungsten(VI) enriched by nanometer-size titanium dioxide in water and sediment.

The adsorption of W (VI) on different metal oxides (TiO(2), ZrO(2)), different crystal form of TiO(2) (rutile, anatase) with high surface areas was studied and compared under different pH. A novel method for preconcentration of W (VI) with nanometer size titanium dioxide (rutile) and determination by spectrophotometry has been developed. W (VI) was selective adsorbed on 100 mg TiO(2) from 250 ml solution at pH 3.0, then eluted by 2 ml 9 mol l(-1) sodium hydroxide solution. The eluent was adjusted to 5 ml pH 0 solution, added 0.5 ml 12 mol l(-1) HCl, 0.3 ml 3% TiCl(3), 0.3 ml 50% NH(4)SCN, stirred for 20 min, used for the analysis of W (VI) by measuring the absorbance at 402 nm with spectrophotometry, based on the chromogenic reaction between the W (VI) and the mixture of TiCl(3) and NH(4)SCN. This method gave a concentration enhancement of 50 for 250 ml sample, eliminated the sizable interferences on direct determination with spectrophotometry. Detection limits (3sigma, n=11) of 1.2 ng ml(-1), relative standard deviation of 2.3% at 10 ng ml(-1) level were obtained. The method was applied to determine the W (VI) in hot spring water, river water, tap water and stream sediment. Analytical recoveries of W (VI) added to samples were 98-101%.