Spectrophotometric determination of titanium(IV) in water with hexasodium 50,51,52,53,54,55-hexahydroxycalix [6] arene-5,11,17,23,29,35-hexasulfonate

Hexasodium 50,51,52,53,54,55-hexahydroxycalix [6] arene-5,11,17,23,29,35-hexasulfonate (denoted as CALX-S6) reacts with titanium(IV) to form a yellow 1: 1 complex in weakly acidic solution. The color reaction took place completely in about 30 min and the color of the solution was stable for more than three days. The absorption maximum was found to be at 403 nm and the absorbance changed remarkably with pH, reaching the maximum value at pH 2.0~2.6. The absorbance at 403 nm was proportional to the concentration of titanium(IV) in the range of 0~4.8 ppm. The molar absorptivity of titanium (IV) was 1.02×104M-1 cm-1. Most of the foreign metal ions and anions, except iron(III), did not produce any coloration with CALX-S6 at pH 2.3. Although a little interference due to foreign ions such as manganese(II), cerium(III), zirconium(IV), hafnium (IV) and phosphate ion including iron(III) was observed, these effects were completely eliminated by the addition of hydroxylamine hydrochloride. Based on these results, a simple and direct spectrophotometric method with high selectivity and sensitivity was proposed. This method was successfully applied to the determination of titanium (IV) extracted into 1 M hydrochloric acid from soil samples.