ANALYTICAL APPLICATION OF O,O'-DIALKYL DITHIOPHOSPHATE .10. EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF CHROMIUM(VI) WITH O,O'-DIBUTYL DITHIOPHOSPHATE

Chromium(VI) reacts with O,O'-dibutyl dithiophosphate ion to form tris(dibutyl dithiophosphato)chromium(III) and tetrabutyl thiophosphoryl disulfide in an acidic solution (pH 1.2 - 1.7). Both of the products are extracted into hexane and the absorbance at 278 nm based on these products is utilized for the determination of chromium(VI). The chromium(III) complex corresponding to two-thirds of the initial chromium(VI) concentration and the disulfide corresponding to three-halves of the initial chromium(VI) concentration are extracted under the optimum conditions. The calibration graph obtained is linear over the range of 2X10(-6) - 1X10(-4) mol/dm3 chromium(VI) concentration, and the apparent molar absorptivity (absorbance per initial chromium(VI) concentration in aqueous phase) is 1.69X10(4) mol-1 dm3 cm-1. This method is subject to interference from Cu(II), Fe(II), Cd(II), Pb(II), Hg(II), Pd(II), Sn(IV), Sb(III), Se(IV), Au(III), nitrite, sulfite, thiosulfate and ascorbic acid. This method was applied to the determination of chromium in steel samples, and good results were obtained.