Ultraviolet absorptiometric determination of titanium with hydrogen peroxide and oxine
1973 Volume 22 Issue 7 Pages 811-815
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1973 Volume 22 Issue 7 Pages 811-815
Titanium forms so stable a ternary complex with hydrogen peroxide and oxine at pH 3.06.3 that the chloroform extract is not immediately decomposed by dilute sulfuric acid. The excess oxine in the organic phase, which interferes the measurement of the absorbance in ultraviolet region, can almost completelywashed out by a single agitation with 2N sulfuric acid solution for two minutes. Thus the sensitivity at 265 nm is eight times as large as at 425 nm. The blank is small and constant, although Hashitani et al. have stated not be so in determinations of palladium and rhodium. Further washing decreases the absorbance. When the concentration of sulfuric acid is increased, the distribution ratio of oxine is remarkably decreased up to 2N and then gradually as shown below. Constant absorbance is obtained with more than 10-3 M hydrogen peroxide and 6 × 10-3 M oxine concentration. The maximum absorption in the ultraviolet region is present at 265 nm. The apparent molar absorptivity is 4.28 × 104, and the sensitivity by Sandell's method is 0.0011 μg Ti/cm2.
For determination of less than 20 μg of titanium in solution, add 1 ml of 0.6% hydrogen peroxide and 2 ml of 1% oxine acetate solution, adjust the pH to 3.03.5 with dilute sodium hydroxide solution and 10 ml of 1 M acetate buffer solution of pH 3, and dilute to 25 ml with water. Extract with 25.0 ml chloroform, wash with 40 ml of 2 N sulfuric acid in another separatory funnel, filter through dry filter paper, and measure the absorbance at 265 nm. Beer's law is obeyed over the titanium concentration range of 1 to 20 μg/ 25 ml chloroform. About 1 mg amounts of aluminum and copper do not interfere, but cobalt, chromium(III), and iron(III) do. In the presence of iron(III), the organic phase becomes colorless when shaken with 2N sulfuric acid, but fairly large absorbance is observed possibly due to an oxidation product of oxine.
Slopes of plots of logarithm of the distribution ratio of titanium against logarithm of total concentrations of hydrogen peroxide and oxine are 1.19 and 2.24, respectively, and that against the pH values is 4.02, which indicates liberation of four protons by the reaction. As titanium and oxine have been shown to exist as TiO2+ and H2+Ox under the experimental conditions, the ternary complex is assigned to be TiO(H2O2) (Ox)2.
2-Methyloxine does not react similarly.
The distribution ratio of oxine between chloroform and sulfuric acid is 1.2 × 10-2, 4.5 × 10-3, 2.4 × 10-3, 1.0 × 10-3, and 5.5 × 10-4 for 1.07, 2.14, 3.22, 4.82, and 6.43N, respectively.
