Micelle mediated extraction of titanium and its ultra-trace determination in silicate rocks

A highly sensitive method for extractive spectrophotometric determination of titanium in silicate rocks is described. Titanium in the range 0-10 microg as TiO2 is extracted into benzene or toluene by the formation of a ternary complex of the metal with thiocyanate (SCN-) and cetyltrimethylammonium bromide (CTA) in the ratio 1:2:2. A deep yellowish-orange ternary complex thus formed is suitable for the determination of titanium at wavelength 421 nm. The optimum colour intensity of this ternary complex was attained when the complex was extracted from an aqueous solution having concentrations of thiocyanate and HCl, in the range, 1.5-2.5 and 1-5 mol L(-1), respectively. The molar absorptivity and Sandell's sensitivity of the extracted species were found to be 1.1-1.0x10(5) L mol(-1) cm(-1) and 0.47 ng cm(-2) (referred to titanium), respectively, at lambda(max) of 421 nm. Except Fe3+, Nb5+ and V5+, no interference was encountered in the estimation of titanium. While up to 10 mg L(-1) Nb and V did not interfere in the determination of titanium, the interference of Fe(3+) was eliminated by reducing it to Fe2+ using SnCl2 solution. The method is highly sensitive and selective. The results obtained for titanium estimation in a host of silicate rock samples have been found to be highly reproducible, accurate and favourably comparable with certified values of reference materials and those obtained from standard methods.