The Chemistry of Indium A Colorimetric Method for the Estimation of Small Amounts of Indium THERALD MOELLER, Noyes Chemical Laboratory, University of Illinois, Urbana, Ill.
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tity corresponding to 1000 mg. of indium per liter of chloroform. Characteristic data are given in Figure 1. Measurements a t concentrations greater than 50 mg. of indium per liter are not included, but the curves obtained differ only in a marked broadening of the absorption band.. Maximum absorption is noted a t 395 mp for most samples, with a tendency to shift to 400 m p at higher concentrations. Inasmuch as this absorption band is rather broad, differences in transmittancy between 395 and 400 m p are in no instance particularly great. Because of this fact and because 400 m p represents the lower limit on some instruments, all further measurements were made a t 400 mp.
suitability of 8-hydroxyquinoline as a reagent for the estimation of small amounts of indium was pointed out by Geilmann and Wrigge ( 5 ) ,who reported that quantitative precipitation of the compound I n ( C ~ H e O N could )~ be effected at 70" to 80" C. from a sodium acetate-acetic acid buffer, and indium then determined either by direct weighing of the precipitate after drying at 120" or by application of the usual bromometric titration procedure after solution of the compound in warm 10 to 15 per cent hydrochloric acid. Accurate results in the concentration range 0.83 to 70.8 mg. of indium were obtained. The possibility of utilizing the 8-hydroxyquinoline derivative of indium for the colorimetric estimation of the element has, apparently, escaped consideration. The compound In(CsHaON), dissolves readily in chloroform (a not unexpected fact, since chelate linkages within the molecule completely satisfy the coordination number of six which is normally shown by indium) yielding bright yellow solutions, the colors of which are of sufficient intensity to be readily detectable even at indium concentrations below 1mg. per liter of solvent. Consequently, it seemed advisable t o investigate this possibility, and the results here reported summarize a spectrophotometric examination of the system and a procedure for the extraction of the metal and its subsequent colorimetric estimation as the 8-hydroxyquinoline complex.
Apparatus and Materials All colorimetric measurements reported herein were made with a Cenco-Sheard spectrophotelometer (Q),using cells of I-cm. (*0.5 per cent) thickness and employing a slit width of 5 mp. Measurements of pH were made with a Beckman Laboratory Model G DH meter, the glass electrode of which was calibrated against a ktandard phthalate buffer. A standard indium sulfate solution containing 11.64 mg. of indium per milliliter as determined grawmetrically by hydroxide precipitation (8) was repared from anhydrous sulfate obtained originally from a sampye pf the metal of 99.98 per cent purity (8). From one portion of this solution, the Indium derivative of 8hydroxyquinoline was prepared according to the directions of Geilmann and Wrigge (6). The washed and dried product analyzed 20.81 per cent indium as compared with 20.97 per cent calculated for In(C,HsON)s. From a second portion of the sulfate solution, a stock indium solution containing the equivalent of 1 mg. of the metal in 10 ml. was obtained by dilution. Chloroform, containing 1 per cent ethanol by volume, was of analytical reagent quality. During the investigation, it was found convenient to recover chloroform containing 8-hydroxyquinoline or its indium derivative by shaking with 6 N sulfuric acid, which completely extracts these materials, distilling from lime, and adding ethanol in the same fashion as recommended for recovery from dithizone extractions ( 2 ) . Chloroform so recovered was colorimetrically indistinguishable from the original material. Indium can be recovered after destruction of the quinoline material (6). The 8-hydroxyquinoline used was an Eastman Kodak preparation, and other chemicals were of the best qualities obtainable. Gallium and thallic sulfate solutions were obtained from the pure oxides.
Extraction and Colorimetric Estimation of Indium Indium, like aluminum and ferric iron ( I ) , can be extracted from aqueous salt solutions by shaking with a chloroform solution of 8-hydroxyquinoline. The procedure followTed in all extractions amounted to vigorous shaking of a 25-m1. aqueous solution of the indium salt with four successive 5ml. portions of a 0.01 M solution of 8-hydroxyquinoline in chloroform. The combined extracts were then diluted to 50 ml. with chloroform before colorimetric examination. At optimum pH values, usually the third, and always the fourth, extract appeared colorless. The marked effect of p H upon precipitations with 8-hydroxyquinoline (3, 4, 6) is also apparent in these extractions (1). The most suitable p H for complete extraction of indium was found by extracting solutions containing the equivalent of 20 mg. of indium per liter of chloroform and adjusted
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Spectrophotometric Examination of Chloroform Solutions of the Indium Derivative of 8-Hydroxyquinoline Spectral transmittancy studies over a wavelength range of 350 t o 700 m p were made upon solutions prepared by dilution to appropriate concentrations of a stock solution containing the indium derivative of 8-hydroxyquinoline in quan-
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FIGURE 1. TRANSMITTANCY CURVESFOR INDIUM DERIVATIVE OF
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8-HYDROXYQUINOLINE IN CHLOROFORM
April 15, 1943
ANALYTICAL EDITION
OF INDIUM IN INDIUM SULFATE TABLEI. ESTIMATION SOLUTIONS
Mg. of Indium per Liter of Chloroform Taken Found Deviation 0.20 $0.10 0.10 0 0.30 0.30 0.60 -0.10 0.70 1.45 -0.05 1.50 0 4.00 4.00 7.90 -0.10 8.00 11.9 -0.1 12.0 16.0 16.0 0 20.0 0 20.0 -0.5 23.5 24.0 33.8 f1.8 32.0
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Plotted in Figure 3 are data obtained from transmittancy studies a t 400 m p upon extracts made a t p H 3.5 from indium sulfate solutions of varying concentrations prepared from the stock solution containing 1 mg. of indium in 10 ml. Beer's law is obeyed a t concentrations up to 18.0 mg. of indium per liter of chloroform, but a t larger concentrations deviations become increasingly great. Intersection of the curve with the zero axis of concentration a t a point below that corresponding to 100 per cent transmittancy is due to the fact that a chloroform solution of 8-hydroxyquinoline, although apparently colorless, shows a slight absorption a t 400 m p (1, 7). Use of constant conditions of extraction obviates this difficulty. 2.000
to various p H values by the addition of either 0.1 N sodium acetate or sulfuric acid, determining the per cent transmittancies a t 400 mp, and comparing these values (through the use of a calibration curve) with the sample showing maximum absorption. I n this manner, the degree of extraction was obtained a t each pH value. Reference to the plot of these results given in Figure 2 indicates that while extraction begins slightly above p H 1.9, it is complete only a t p H 3.2. Complete removal of indium occurs within the pH range of 3.2 to 4.5, and in all subsequent extractions a pH of 3.5 was employed.
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FIGURE 3. RELATION BETWEEN TRANSMITTANCY AND INDIUM CONCENTRATION
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The reproducibility and accuracy of the method are indicated by the data in Table I. I n the range of 0.30 to 20.0 mg. of indium per liter of chloroform, deviations are small, but a t higher and lower concentrations they become marked. If concentrations be expressed in terms of actual indium content instead of per liter of chloroform, the sensitivity of the method is apparent. Since given concentrations were obtained from 50-ml. chloroform solutions, accurate measurements resulted with actual indium contents in the range 0.015 to 1.00 mg.
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FIGURE 2. EFFECTOF pH UPON EXTRACTION OF INDIUM
The p H values given in Figure 2 are for the aqueous solutions before shaking with the 8-hydroxyquinoline reagent. During the extraction process, some of the amine enters the aqueous phase with an attendant increase in pH, but under standard conditions of extraction, the initial p H appears to be the more readily attainable and therefore the more important. When the p H is 1.9 or less, 8-hydroxyquinoline is completely extracted from the chloroform owing to combination with the acid, and a t p H values above 4.5, precipitation of hydrous indium hydroxide both decreases the amount of extractable indium and renders layer separation difficult through emulsification of water in chloroform.
Nitrate, chloride, or sulfate solutions containing in 25-ml. portions the equivalents of 20 mg. of various metals per liter of chloroform (on the basis of complete extraction) were extracted a t pH 3.5 by the above procedure, transmittancies a t 400 mp being determined. The following ions were not extracted under these conditions: magnesium, calcium, strontium, zinc, cadmium, mercuric, stannic, lead, manganous, chromic, and silver. The following ions yielded extracts showing transmittancies below that for 8-hydroxyquinoline and were, therefore, extracted (at least in part): aluminum, gallium, thallic, stannous, bismuth, cupric, ferric, ferrous, nickel, and cobalt (slightly). Ions of the latter group would interfere with the estimation of indium by this method. Estimation of indium should be possible in the presence of any ion not extractable at p H 3.5. I n Table I1 are summarized data for determinations made in the presence of varying quantities of zinc, cadmium, and lead ions, concentrations again being expressed relative to 1 liter of chloroform. The feasibility of the procedure is apparent. Since the most persistent impurity in indium is iron, a method for the estimation of indium in the presence of iron would be of value. Application of the present procedure
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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TABLE11. ESTIMATION OF INDIUM IN PRESENCE OF ZINC, CADMIUM, OR LEAD (20.0 mg. of indium per liter of chloroform taken in all cases) Impurity Added Indium Found Ion Mo. Mo Zn++ 20 20.0 100 20.0 20.0 200 20.0 Cd++ 20 20.0 100 20.0 200 20.0 Pb++ 20 20.0 100a Some precipitation of lead sulfate noted.
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would be feasible if it were possible to extract either ferric iron or indium to the exclusion of the other a t an appropriate pH. However, since the extraction of the ferric derivative of 8-hydroxyquinoline is complete only a t pH values above 1.9 to 2.0 (1, 7) whereas extraction of indium begins in this p H interval] such a procedure would not appear to be suitable. Furthermore, the extensive absorption of the ferric complex a t 400 mp (7) would cause any iron unextracted a t a pH lower than 1.9 to interfere with indium extracted a t pH 3.5. Attempts a t successive extractions of iron and indium have fully demonstrated the lack of reliability of such a procedure.
Summary The 8-hydroxyquinoline derivative of indium dissolves readily in chloroform, yielding yellow solutions which show a fairly broad absorption band in the region of 395 to 400 mp. At 400 mp, such solutions obey Beer’s law in concentrations up to 18.0 mg. of indium per liter of chloroform and lend themselves to the colorimetric estimation of the element. Indium ion can be completely extracted from aqueous
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solutions in the pH range 3.2 to 4.5 by shaking with a chloroform solution of 8-hydroxyquinoline. Of the commoner ions, only the following are extracted at pH 3.5 and therefore interfere with the colorimetric estimation of indium in the chloroform extracts: aluminum, stannous, bismuth, ferric, ferrous, cobalt, nickel, and cupric. Gallium and thallic ions also interfere. Indium can be estimated accurately in the presence of considerable quantities of zinc, cadmium, and lead ions, but it appears impossible to determine indium accurately in ferricindium ion solutions by extraction of ferric iron a t a low pH and subsequent extraction of indium followed by colorimetric examination. The colorimetric procedure yields accurate results for indium concentrations in the interval of 0.3 to 20 mg. per liter of chloroform or 0.015 to 1.00 mg. of the metal in a 25-m1. aqueous solution. Analyses of samples containing larger amounts of indium should be possible through sufficient dilution of the chloroform extract.
Literature Cited (1) Alexander, J. W., in “Summaries of Doctoral Dissertations, University of Wisconsin”, Vol. 6, p. 205, Madison, Wis., University of Wisconsin Press, 1942. (2) Biddle, D. A., IND. ENQ.CHEM.,ANAL. ED.,8, 99 (1936). (3) Fleck, H. R., Analyst, 62, 378 (1937). Ibid., 58, 388 (1933). (4) Fleck, H. R., and Ward, A. iM., ( 5 ) Geilmann, W., and Wrigge, F. W., 2.anarg. allgem. Chem., 209, 129 (1932). (6) Got8, H., Science Repts. TBhoku I m p . Univ., First Ser., 26, 391 (1937); 26, 418 (1938). (7) Moeller, T., IND.ENQ.CHEW,ANAL.ED. (forthcoming). (8) Moeller, T., J . Am. Chem. Sac., 62, 2444 (1940). (9) Sheard, C., and States, M. N., J . Optical Sac. Am., 31, 64 (1941)
THIS is the seventh in a seriea of articles, t h e first six of which have appeared 8s follows: J . Am. Chem. SOC.,62, 2444 (1940): 63, 1206 (1941); 63, 2625 (1941); 64,953 (1942); J . Phys. Chem., 45, 1235 (1941); 46,794 (1942).
The Dead-Stop End Point As Applied to the Karl Fischer Method for Determining Moisture GRANT WERNIMONT
AND
F. J. HOPKINSON, Eastman Kodak Company, Rochester, N. Y.
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HE! chemical reaction involved in the Karl Fischer method (2) for determining water was given originally as follows: 2H90 I* SOz.2CsHsN f 2CsHsN = (CsHsN)2H2S0, 2CsH6N.HI
+ +
+
Smith, Bryant, and Mitchell (4) have shown that the reaction is not so simple as this and that it occurs in two distinct steps : 12
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