Anulytico C&mica Acta. 89 (1977) 199-202 @Ekevier Scientific Publishing Company. Amsterdam - Printed in The Netherlands

Short Communication

THE SPECTROPHOTOMETRIC DETERMINATION OF TITANIUM(IV) WITH SODIUM 2-BROMO-4,5-DIHYDROXYAZOBENZENE-4’SULFO- NATE IN ?uE PRESENCE OF CETY~TRIMETHYLAMMONIUM CHLORIDE

YOSHINOBU WAKAMATSU

Deportment of Industrial Chemistry, Hachinohe Technical College. Hachinohe 031 (Japan)

(Received 19th April 1976)

The for&&ion of ternary complexes often improves the sensitivity and selectivity ol an analytical method. During studies on the sensitizing effects of cationic surfactants on the reaction of sodium Z-bromo-4,5dihydroxy- azobenzene-4’-sulfonate (abbreviated as BDAS) with various metal ions [l, 21, the addition of cetyltriiethylammonium chloride (CTMAC) to the titanium(W)-BDAS complex was found to produce a large bathochromic shift in the wavelength of maximum absorption, and a marked increase in the molar absorptivity. This communication describes a sensitive method for the spectrophotometric determination of titanium(IV) by means of this ternary complex. The sensitivity is comparable to, or greater than that df methods based on hydrogen peroxide and xylenol orange [ 3],4(2-pyridylazo)- resorcinol [ 41’ or chromazurol S [ 51; 1,3&phenylguanidine and indoferron [6] or tiron [7] ; hexamethylenetetramine and stilbazo [8] ; or diantipyryl- methane and pyrogallolsulfonic acid [9] _

Experimental Reagents The BDAS used was synthesized from 4bromopyrocatechol

and sodium sulfanilate as described previously [l] . A standard titanium(W) solution was prepared by dissolving the hydrolysis

product of pure titanium(W) chloride in 3 M sulfuric acid and diluting with water. It was standardized compleximetrically and diluted with water as required.

The CTMAC solution was prepared in aqueous 20 % (v/v) methanol. All theether chemicals used were of analytical grade. Appam&s. A Hitachi model 124 spectrophotometer with lo-mm quartz

cells and a Toa Dempa model HII-5-4 pH meter were used. Procedure. Transfer an aliquot of titanium(IV) solution to a 25-ml volu-

metric flask. Add 4 ml of lo-’ M BDAS, 10 ml of buffer solution (0.25 M monochloroacetic acid and 0.25 M sodium acei&& adjusted to pH 2.8--3-O), and 3.5 mi of lo-’ M CTMAC. Dilute to the mark with water. Measure the absorbance at 515 nm against a reagent blank.

200

Resu!ts and discussion Absorption spectra. The absorption spectra of the reagent and its titan-

ium(W) chelate at pH 2.9 in the presence of an excess of CTMAC are shown in Fig. 1. Included for compariion is the spectrum of the binary titanium(W)- BDAS chelate formed at pH 5.0. The ternary complex has an absorption maximum at 515 nm and is stable for at least several hours. The binary com- plex with its absorption maximum at 490 nm is stable at pH 5 for several hours, but is completely dissociated below pH 3. For the determination of titanium, the ternary complex is superior to the binary one in regard to sensitivity and selectivity.

Effects of experirzental condition s. Standard amounts of titanium(W), BDAS and CTMAC solutions were buffered at varying pH values. A plot of absorbance against pH showed that maximal and constant absorbance was obtained at pH 2.6-4.6. Subsequent determinations were carried out at pH 2.9, because the absorbance of the reagent blank increased markedly above pH 3.5.

The effect of the CTM_IAC concentration on the complex formation was investigated for solutions con’taining 9.4 pg of titanium (7.8 - IO+ M). Maximum color formation was found when the CTMAC concentration exceeded 8.0 - lo4 M. It was also found that both the titanium(IV) complex and the reagent are precipitated when less than about 3 - lOA M CTMAC is added. This suggests that the uncharged titanium(IV)-BDAS-CTMAC and BDAS-CTMAC species are present as finely dispersed particles protected within the CTMAC micelles in solution.

The effect of the BDAS concentration on the cola: formation-was then investigated by varying the BDAS concentration. A constant absorbance was obtained when the BDAS concentration exceeded 1.0 - 1W4 M.

Calibration curue. With the above optimal conditions, a linear calibration curve was obtained over the concentration range O-14 pg of titanium. The

Fig. 1. Absorption spectra..(I) [BDAS j = 1.6 - 10’ $1; [CT%iACj = 1.4 * 10e3 M; pH 2.9; reference, water. (II) [Ti] = 9.4 ug (7.8 * IO-’ &I); [BDAS] = I.6 * lOti M; [CTMACj = 1.4 - 10-j M: pH 2.9: reference. reagent biank. (III) [I?] = 9.4 ~6; [BDAS] = 1.6 l 10’ M; pH 5.0; reference, reagent blank.

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apparent molar absorptivity was calculated to be 6.2 - 10’ 1 mol-’ cm-’ at 515 nm, and the sensitivity of the reaction was 7.3 - 1W4 pg cm-*.

Nature of complex. The titanium : BDAS ratio in the ternary complex formed at pH 2.9 was determined by the continuous variations method to be 1 : 3. The mole ratio method confirmed this conclusion.

Effect of foreign ions. The effect of foreign ions on the determination of 9.6 ccg of titanium was studied. Of the anions examined, chloride, nitrate and sulfatz ions showed no interference at alI concentrations; fluoride, thiosulfate, citrate and nitrilotriacetate ions did not interfere in lOO-fold molar amounts, or tartrate and phosphate ions in lo-fold amounts. Perchlorate ion, however, must be absent.

About lOO-fold concentrations of divalent metal ions, such as nickel, cobalt, cadmium, zinc, lead, calcium and magnesium, did not interfere. The results for the othe? ions examined are presented in Table 1. Some of the interfering ions could be masked by EDTA, although too large excess of EDTA gave negative errors.

The color development of the ternary complex was retarded by addition of EDTA. The reaction time was measured in the absence of EDTA and in the presence of 8.0 - 10e4 M EDTA (100 times that of the titanium), the EDTA being added before the BDAS. About 100 min was required to obtain maximal absorbance of the ternary complex in the presence of EDTA, only a few min being sufficient when it was absent. If EDTA is used as a masking agent for interfering ions, therefore, the absorbance should be measured 2 h after preparation of the final solution.

Analysis of standard steel sample. The proposed method was applied to the determination of titanium in a s+ndard steel sample NBS 6f. The proced- ure was as follows: decompose the sample with equal volumes of hydrochloric and nitric acids, and after removal of insoluble materials, separate the iron(III) by ether extraction froin a 6 M hydrochloric acid solution; add EDTA as a

TABLE 1

Effect of foreign ions for the determination of 9.6 ug Of titanium(IV)

Ion Added Ti found

((Ionlif’I’il) bg)

Ion Added

([Ionl/[Til)

Ti found

bg)

Cu(I1) 50 Ga(III) 1

10 AI(II1) 50

IR(III) 5: Fe(II1) 1

50

9.7 11.8

9.k 9.8 9.8

10.2 12.0

9.6=

TAW) Zr( IV)

UWI) W(W).

Mo(V1)

50 1 1 1 1

10 1 1

10.2 11.5

9.9= 10.1 11.1 lO.Ob

17.3 13.4c

“2 ml of lo-’ M EDTA added. bl mi of 0.1 M sodium citrate added. =2 ml of lo-’ M

sodium tartrate added.

2.02

masking agent for minute amounts of iron and other interfering ions, and determine the titznium content as described zzbove.

An average value of 0.061 SE was ob+dned (certificate value, 0.063 5%).

The author is grateful to Dr. M. Otomo of Nagoya Iz&itute of Technology for his critical rezding of the preliminary manuscript 2nd valuable suggestions.

REFERENCES

I Y. Wakamatsu and &I. Otomo. Anal. Chim. Acta. 79 (1975) 322. 2 Y. \Vakamatsu and hi. Otomo. unpubiished. 3 h!. Otomo, Bull. Chem. Sot. Jpn.. 36 (1963) 1331. 4 T. Ozawa, BuF_seki Kagaku, 16 (1967) 435. ti H. Nishida. Bunseki Kagaku. 19 (1970) 30. 6 Y. Wakamatsu and M Otomo. Bunseki Kapaku. 20 (1971) 862. 7 Y. Wakamatsu and ZIl. Otomo. Bull. Ciiem. Sot. Jpn., 45 (1972) 2764. 8 T. Owwa. Nippon Kagnku &s&i. 92 (1971) 522. 9 A. I. Busev and N. G. Solovieva. Zh. Anal. Khim., 27 (1972) 1283.