100
A N A L Y T I C A L C H E M'I S T R Y
Although this method does not qualify as one of extreme accuracy, i t does offer for the first time a means of estimating pyroand triphosphoric acids, or their salts, i n the presence of one another. Since i t can also be used in the presence of both orthoand metaphosphates, i t offers a means of determining the composition of the soluble phosphate glasses as well as mixtures of the dehydrated phosphates. ACKNOWLEDGMENT
The author wishes to thank Howard Adler and Vir. H. Koodstock for many helpful suggestions and criticism and A. R. Wreath for the sodium oxide determinations shown in Table I. LITERATURE CITED (1)
Andress, K. R., and Wust, K., Z .
anorg. allgem. Chem., 237,
113-31 (1938).
(2)
Britske, E. V., and Dragunov, S. S., J . Chem. I n d . (Moscow),
(3)
Fiske, C. H., and Subbarow, Y . , J . Biol. Chem., 66, 375-400.
4, 49 (1927). (1925).
(4) Fleitman, T., and Henneberg, W., Leibigs Ann., 65, 30, 387 (1845). (5)
Gerber, A. B., and Miles, F. T., IND.EXG.CHEM.,A x . 4 ~ .ED.,
10, 519 (1938). (6) Ibid.. 13. 406-11 (1941). (7j Jones, L: T., Ibid.; 14, k36 (1942). (8) Kiehl, S. J., and Coats, H. P., J . Am. Chem. Soc., 49, 2180 (1927). (9) Partridge, E. P., Hicks, V.,and Smith, G. W., Ibid., 63, 454 (1941). (10) Travers, A . , and Chu, P.K., Helv. Chim. Acta, 16, 913 (1933). PRESENTED before the Inorganic and Analytical Group at the Fiftieth Anniversary One-Day Technical Conference of the Chicago Section of the AMEIICAX CHEvIcAL SOCIETY, November 16, 1945.
Colorimetric Determination of Titanium with Disodium- 1,2-d ihydroxybenzene-3,5 - disuIf o nate JOHN H. YOE AND ALFRED R. ARMSTRONG', University of Virginia, Charbttesville, Vu. The reagent used by Yoe and Jones for determining ferric iron has been applied, to titanium. It is sensitive to 1 part of titanium in 100,000,000 parts of solution when observations are made in 50-ml., tall-form Nessler cylinders. Over the pH range 4.3 to 9.6 the tint and intensity of the color remain nearly constant. The yellow colored complex obeys Beer's law over the useful range of concentrations. The effect of diverse ions has been studied and the tolerance to interfering substances determined. Interference caused by ferric iron may be eliminated by reducing it to the ferrous state with sodium dithionite in solutions buffered at pH 4.7. A number of National Bureau of Standards samples have been analyzed with accuracy. With three samples the absorbency caused by the blue ferric complex was measured spectrophotometrically at 560 mp, sodium dithionite added, and the absorbency caused by the yellow titanium complex measured at 410 mp; thus both constituents were determined with the one reagent.
T
H E phenolic compounds which have been investigated as colorimetric reagents for titanium include salicylic acid (S), thymol ( 2 ) , pyrocatechol (5, 6 ) , gallic acid (1, 7 ) , and chromotropic acid (4, 8, 9). Most of these compounds are unstable in solution. The number of interfering substances is relatively large; hence, none has been used extensively for the determination of titanium. Yoe and Jones (If) reported a study of disodium-1,2-dihydroxybenzene-3,5-disulfonate as a coldrimetric reagent for iron and suggested its use for the colorimetric determination of titanium. The reagent forms a stable lemon-yellow titanium complex of high sensitivity. The intensity of the color is nearly independent of pH over a range of 4.3 to 9.6. Interference caused by ferric iron may be eliminated by reducing the iron n-ith sodium dithionite solution buffered a t pH 4.7, so that titanium may be determined in the presence of iron. Disodium-1,2-dihydroxybenzene-3,5-disulfonate is distributed by the LaMotte Chemical Products Company, Baltimore, Md. HzO,molecuThe formula for the reagent is CsH2(OH)2(S020Sa)2 lar weight 332.2. Ignition of a sample of the reagent with sulfuric acid in a platinum crucible left a residue equivalent to 13.8Oy0 sodium in the compound. The theoretical value is 13.847, sodium. The water of crystallization is not lost a t 180" C. (IO). The name Tiron is suggested because the reagent may be used for the colorimetric determination of both titanium and iron. 1 Present address, Department of Chemistry, College of William and Mary, Williamsburg, Va.
APPARATUS AND SOLUTIONS
Instruments. Spectrophotometric measurements were made with a Beckman spectrophotometer, Model D, using 10.00-mm. Corex glass transmission cells. The band width varied between 3 and 5 mp. Visual observations were made with 50-ml. (220-mm.) Sessler cylinders. The pH measurements were made with a glass electrode. Reagent Solution. A solution containing 4 grams pf disodium1,2-dihydroxybenzene-3,5-disulfonate in 100 ml. of water \vas used. The water-clear solution becomes pale yelloTv on aging several weeks and should then be discarded. Standard Titanium Solution. A standard titanium solution was prepared from 20% titanous chloride solution by dilution with 0.5 molar sulfuric acid and adding 3% hydrogen peroxide until a faint yellow color persisted. The solution became colorless on standing a week. The titanium content vas determined gravimetrically as the oxide and adjusted to 100 p.p.m. This solution showed no indication of hydrolysis after standing eight months. Solutions of Diverse Ions. The solutions used in studying the effect of the various ions on the t,int and intensity of the titanium complex were prepared from reagent grade salts which were essentially free of titanium and iron. The solutions generally contained 1 mg. of the desired ion per ml. BulTer. A buffer solution having a pH of 4.7 was prepared by mixing equal volumes of molar acetic acid and molar sodium acetate solution. SPECTROPHOTOMETRIC STUDIES
The spectral transmittancy curves for 1 p.p.m. titanium (I), 5 p.p.m. iron (11), and 500 p.p.m. sodium dithionite (111) are
V O L U M E 1 9 , NO. 2, F E B R U A R Y 1 9 4 7
101 to 0.4 p.p.m. of titanium. I n this range solutions differing by 0.03 p.p.m. can be differentiated. The spot-plate sensitivity was determined by transferring 0.05-ml. drops of successively more dilute standard titanium solutions to depressions in a white porcelain spot plate and adding 0.05 ml. of reagent solution (4 grams per 100 ml.) and a drop of 0.3 molar ammonia. The lowest concentration of test solution to give a distinguishable color contained 2 p.p.m. of titanium; thus 0.1 microgram of the metallic ion in 0.05 ml. of solution may be detected by the spot test. PERMANENCY O F STANDARDS
400
450
500
550
600
Wave Lenpth, nw.
Figure 1.
Spectral Transmittancy
The concentration of reagent is a factor in the rate of development and stability of the color. With 1 p.p.m. of titanium and 20 mg. of reagent per 100 ml. fading began in 24 to 48 hours. When the amount of reagent was increased to 100 mg. per 100 ml. of solution the color intensity increased nearly 1% in 2 weeks, 2% in 5 weeks, and 5y0in 18 weeks. The increase in absorption may have been the result of slow oxidation of the reagent. The useful life of the standards is a t least 2 weeks.
Disodium-1, 2-dihydroxybenzene-3, 5-disulfonate reagent 1.
1 p.p.m. T i + + + +plus reagent. 11. 5 p.p.m. F e + + + plus reagent. 111. 500 p.p.m. sodium dithionite
given in Figure 1. In each case the solution contained the recommended concentration of buffer and disodium-1,2-dihydroxybenzene-3,5-disulfonate: 5 millimoles each of sodium acetate and acetic acid, and 0.4 gram of reagent per 100 ml. The p H of the solution was 4.7. The curve for the dithionite is included because this substance is used in the procedure for titanium. These curves show that the transmittancy of the iron complex can be measured a t a wave length of 560 mp without interference from the titanium. On addition of sodium dithionite the color of the iron complex is destroyed. The transmittancy of the titanium complex may then be measured a t a wave length of 410
nu. Dilute dithionite solution is colorless when observed in Nessler cylinders; it does, however, absorb wave lengths shorter than 410 mp (see Figure 1). Hence in the spectrophotometric determination of titanium all transmittancy measurements are made a t 410 mp rather than at' the wave length of maximum absorbency (-log T ) , 380 mfi.
EFFECT OF DIVERSE IONS
T o measure the effect of diverse ions on the color complex, solutions containing 0.03 mg. of titanium, a measured volume of standard solution of diverse ion, reagent (0.4 gram), and buffer (10 ml.) were diluted to 100 ml. These solutions were compared in both Sessler cylinders and spect,rophotometricallywith standards containing 0.027, 0.030, and 0.033 mx. of titanium per 100 ml. If the prescnce of the diverse ion caused no off-tint and the intensity remained nearer the intermediate standard, it was said not to interfere. The tests for interference were repeated on solutions containing, in addition to the titanium, buffer, and reagent, 50 mg. of sodium dithionit,e per 100 ml. When added in the concentration indicated (p.p.m.) no interference was observed with the following ions: Asttf (20), As04--- (20 As), Ba07-- (100 B), BOs--- (200 B), Be++ (loo), Br- (2500), Cd++ (300), C1- (SOOO), I- (lOOO), Mg++ (loo), h4n++ (250), SOa- (1250), HPO,-- (1000 PtOj), Zn++ (500), succinate (1200), biphthalate (0.05 molar). N o data were obtained on higher concentrations. The ions showing interference with the limiting concentrations which can be tolerated are given in Table I. CLASSIFICATION OF INTERFERING SUBSTANCE
APPLICATION O F BEER'S LAW
Experiments showed that the intensity of the color increased with the reagent-titanium ratio, rapidly a t first and slowly even at the highest ratio. As the color intensity depends on the con,centration of the reagent, a large excess is required to obtain conformity to Beer's lay. With t'he recommended concentration of reagent (400 mg. per 100 ml. of solution) the system follows Beer's law to a t least 4 p.p.m. of titanium. Higher concentrations of the metal were not prepared because the color intensities would have been above the practical limit for spectrophotometric measurement. SENSITIVITY OF THE REACTION
Solutions containing 0.40 gram of reagent and 10 ml. of buffer per 100 ml. of solution together with 1part of titanium in 10,000,$000,25,000,000, 50,000,000, 100,000,000,and 200,000,000 parts of solution and a reagent blank were transferred to Sessler cylinders. After shuffling, the tubes could be rearranged in correct order through a concentration of 1 part in 100,000,000. The wave length of maximurn absorbency lies outside the visible region. -4s a result 1 part of the titanium in 200,000,000parts of solution may be readily detected spectrophotometrically. For comparison i n Nessler cylinders 0.01 to 0.8 p.p.m. of titanium is the useful concentration range. The region of greatest sensitivity between small fixed increments i n concentration is 0.1
Ions Giving Color Reactions. VO++ forms a purple, and Mo04--, OsOd--, and UOn++ form yellow complexes with the reagent; hence these ions must be absent. Table I. Ion AI++-+
p;+
++
Ca'+ Ce'++ co-+ CrT-+ Cu++ +; ; +
-
Hg+-
?dOOa--
N1++
Pb-+ Sb+*+ &?Os--
SiOg-sn-+++ Th++++ u O;+++ 1' 0 WO4--
ZrO + Citrate Oxalate Tartrate +
Tolerance to Interfering Ions Added as
Limiting Concentration, P.P.M. NazSnO4 XazSdh absent present
'
ANALYTICAL CHEMISTRY as 3 p.p.m. of titanium and 10 p.p.m. of iron can be analyzed spectrophotometrically. For visual comparison of the blue iron color with similar standards, observe the cylinders through a filter cutting out wave lengths below 530 mp which eliminates interference by the titanium.
Table 11. Determination of Titanium and Iron N.B.S. Sample Argillaceous stone 1A
lime-
Ti02 N.B.S.,
TiOz Found,
Difference,
%
%
%
Fe01 N.B.S., %
Fe01 Found,
Differ. ence,
%
%
0.164
0,192a 0.028 1.63 1.62 -0.01 1.67 0.04 0.190a 0.026 0.185a 0.021 1.59 -0.04 Feldspar 70 0.002 0.03 0.029 0.0027 O.OoO7 -0.001 0.0020 0.0000 0.026 -0,004 0.0024 0.0004 0.026 -0,004 Fluorspar 79 0.15 0.0043 0.0013 0.003 0.138 -0,012 0.0040 0.0010 0.131 -0,019 0,0044 0.0014 0.136 -0,014 Soda-lime glass 80 0.024 0.02 0.004 ... ..... 0.021 0,001 ... .,... .. 0.023 0.003 ... ..... .. Glass sand 81 0,095 0.094 -0.001 ... ..... .. -0.003 ... 0.092 .. ..... -0,001 0.094 .. ... ..... When samples were opened up according t o procedure recommended on N.B.S. certificates of analysis, Ti02 percentages were 0.159,0.171,0.162,giving an average TiOz, content of 0.164%. Silica residues were found to contain traces of TiOn which were determined and included in values reported in table.
..
DETERMISATION OF TITANIUM AND IROS I S VARIOUS MATERIALS
The reagent was applied to the determination of titanium in a representative group of Kational Bureau of Standards samples. I n three of the samples iron was also determined. The results (Table 11) show that disodium-1,2dihydroxybenzene-3,5-disulfonate mag be applied successfully to the determination of titanium and iron in the same solution. The values obtained are well within the range of values reported by the bureau. METHODS OF ANALYSIS
Iron gives a red color with disodium-1,2-dihydroxybenzene3,s-disulfonate in alkaline solution and a blue in acid solution. The blue color is bleached by reduction of the ferric iron to the ferrous state with sodium dithionite in solutions with pH less than 5 . As the titanium color does not develop its maximum intensity below pH 4.3, the solution must be buffered in the range pH 4.3 to 5.0. At pH 4.7 solutions containing 50 mg. of reducing agent per 100 ml. become turbid in about 20 minutes; he tendency to precipitate sulfur increased with acidity. Oxidizing agents other thah ferric ion interfere. Vigorous agitation of the solution containing dithionite must be avoided because oxygen of the air consumes the reducing agent and the blue color reappears. Ions That Consume Reagent. h l + f ” , Ca++, Ce+++, Hg++, Pb++, Sn++++,T h L + + + ,ZrO++, and WOd-- consume reagent and cause a diminution in the color intensity of the titanium complex. Tolerance to these ions is increased and the interference is largely overcome by using a large quantity of reagent as recommended in the procedure. Tungsten forms a colorless complex showing strong absorption a t the wave length 410 mp; hence in the spectrophotometric measurement it also behaves as an ion giving a color reaction. Anions Forming Titanium Complexes. Certain anions compete with the disodium-1,2-dihydroxybenzene-3,5-disulfonate for the titanium and thus prevent the full development of the color. By using a high concentration of the reagent the bleaching effect of the negative ions is reduced until only fluoride interferes seriously. PROCEDURE
Weigh out a sample of the material of such size that a convenient aliquot of its solution will contain 0.01 to 0.08 mg. of titanium. Open up the sample by use of suitable solvent or flux. If interfering ions are present in quantities exceeding the tolerances shown in Table I, remove them by the usual methods of separation. Make up the solution to volume in a volumetric flask. For visual comparison transfer an aliquot containing not more than 0.04 mg. of titanium to a 50-ml. Nessler cylinder, add 5 ml. of disodium-1,2-dihydroxybeneene-3,5-disulfonate solution ( 4 grams per 100 ml.) and ammonia until the solution is neutral to Congo red paper. Add 5 ml. of buffer, dilute to the mark, and mix thoroughly. Add 25 mg. of sodium dithionite and dissolve it with a minimum of agitation. Compare (within 15 minutes after the addition of the dithionite) v i t h previously prepared standards covering the range of concentrations likely to be encountered. Since the standards are iron-free, no dithionite is used in their preparation and their color is stable for a t least 2 weeks. For the determination of titanium and iron in the same sample, measure spectrophotometrically a t 560 mp the absorbency caused by the iron complex, add dithionite, and measure a t 410 mp the absorbency caused by the titanium complex (see Figure 1). When the amounts of iron and titanium differ in oider of magnitude it is necessary to use separate aliquots of suitable size for the determination of each metal. Solutions containing as high
The argillaceous limestone was ignited in a platinum crucibIe and leached with hot concentrated hydrochloric acid. The silica residue was filtered off, the filtrate was diluted to volume, and the iron and titanium were determined colorimetrically with disodium1,2-dihydroxybenzene-3,5-disulfonate. The silica residue wa5 fused with sodium carbonate, the melt dissolved in hydrochloric acid, and the iron and titanium content of the solution determined. The silica residue contained no iron but about 10% of the titanium (see Table 11). The feldsDar was treated with hydrofluoric, nitric, and sulfuric acids in a platinum crucible and kvaporated to fumes of sulfur trioxide. The sulfates were dissolved in warm dilute sulfuric acid and the residue was filtered off, fused with sodium carbonate, and taken up in hydrochloric acid. The combined acid solutions were poured into excess sodium hydroxide solution which held the aluminum in solution xhile precipitat,ing the iron and titanium. The precipitated hydroxides were filtered, washed, and dissolved in hydrochloric acid, and the titanium and iron were determined with disodium-1,2-dihydroxybenzene-3,5-disulfonate. The fluorspar was treated with hydrofluoric, nitric, and perchloric acids and evaporated to dryness. Then perchloric acid was added and evaporated off twice more. The residue was dissolved in hydrochloric acid, the solution filtered, and ammonia mater added until alkaline. The precipitated hydroxides were filtered, dissolved from the paper with dilute hydrochloric acid, and titanium and iron were determined in an aliquot of the solution. The soda-lime glass was fused with sodium carbonate and the melt treated with dilute hydrochloric acid. The residue was fused with potassium bisulfate, then again with sodium carbonate. The titanium and iron were separated from calcium by precipitation viith ammonia, filtered, and dissolved in hydrochloric acid, and the titanium was determined. The glass sand was evaporated twice with hydrofluoric and sulfuric acids and taken up in dilute hydrochloric acid. After filtering, the residue was fused with potassium bisulfate and the melt leached with water. The small insoluble fraction was fused with sodium carbonate and dissolved in dilute hydrochloric acid. The three acid solutions were combined and diluted to volume and the titanium was determined. LITERATURE CITED
(1) Das-Gupta, P. N., J . I n d i a n Chem. Soc., 6 , 855 (1926). (2) Lenher, V., and Crawford, W. G., J . Am. Chem. SOC.,35, 141 ( 1913).
(3) Muller, J. H., Ibid., 33, 1508 (1911). (4) Panchenko, G. A,, and Raetakii, Vi, V., J . Applied Chena. (U.S.S.R.), 8,718 (1935). (5) Picard, J., Ber., 42,4343 (1909). (6) Pike, N. R., Ficklen, J. B., and Newell, J. K., Ibid., 68B, 1023 IlR.?Fj\. -
\ - - - - I
(7) Shemyakin, F. M.,and Neumolotova, A. J., J . Gen. Chem. (U.S.S.R.), 5, 491 (1935). ( 8 ) Tananaev, N. A , , and Guntsburg, A., J . Applied Chem. (U.S. S.R.), 11, 364 (1938). (9) Tananaev, N. A , , and Panchenko, G. A., 2. anorg. allgem. Chem., 150, 163 (1926). (10) Winthrop Chemical Co., private communication. (11) Yoe, J. H.,and Jones, A. L., IXD.ENG.CHEM.,AXAL.ED., 16, 111 (1944): cf. Yoe, J. H., and Armstrong, A. R., Science, 102,207 (1945)
