pressure of 1.5 nini. of mercury), ability to recover sample (although the chemical form may be altered), and easy detection of errors due to impurities (other than isotopic nitrogen.) Most of the difficulties with the optical spectroscopic method are not fundamental but may be overcome by precautions or further development. The sample tubes should be kept as free from water, ammonia, organic solvents, and stopcock grease as possible to reduce the background to a mininium. ACKNOWLEDGMENT
The authors nish to thank T. I. Taylor, Columbia Vnirersity, for providing the nitrogen and nitric oxide gas calibration samplcs. They also are indebted to the nicmbers of the ?\lass Spectronwtrg Section :it the Yational Bureau of Standards for measurement of the calibration samples. Demonstration of technique by Sinioii Rothberg, discussion and advice from R. E. Ferguson and technical assistance froin ,Johan
deGroot are also gratefully acknowledged. LITERATURE CITED
(1) Artaud, J., Blaise, J., Gerstenkorn, S., Spectrochim. Acta 10, 110-18 (1957). (2) Brody, J. K., J . Opt. SOC.Am. 42, 408-15 (1952). (3) Brody, 5. K., Fred, &I.,Tomkins, F. S.,Spectrochim. Acta 6, 383-412 (1954). (4) Brody, J. K., Tomkins, F. S., Fred, M., Ibid., 8, 329-47 (1957). (5) Broida, H. P., Morgan, G. H., d s . 4 ~ . CHEM.24. 799-804 11952). (6) Broida, H. P., Morbwitz,’H. J., Selgin, M., J . Research Natl. Bur. Standards 52, 293-301 (1954). ( 7 ) Broida, H. P., Moyer, J. W.,J . Opt. SOC.Am. 42, 37-41 (1952). (8) Clusius, K., Angew. Chem. 66,497-506 11954). (9j Clusius, K., Becker, E. R., 2. ~Vaturforsch. 2a, 154-9 (1947). (10) Crossvhite, H. AI., Fastie, W.G., J. Opt. SOC.,4nz. 46, 110-15 (1956). (11) Dentsov, Y. P., Striganov, A. R., Zhur. Anal. Khim 12, 5-9 (1957). (12) Dicke, G. H., U. S. Patent 2,585,901 (Feh. 19, 1952). (13) Fassel, V. A, Hettel, H. J., Spectrochive. Acta 7, 175-8 (1955).
(14) Fastie, W.G., J . Opt. SOC.-4m. 42, 641-7 (1952). (15) Ferguson, R. E., Broida, H . P., ANAL.CHEM.28, 1436-8 (1956). (16) Hoch, IM., Weisser, H. R., H c l ~ . Chim. Acta 33, 2128-34 (1950). (17) Hunt, D. J., Pish, G., J . Opt. SOC. Am. 46, 87-91 (1956). (18) Kostkowski, H. J., Broida, H. P., Ibid., 46, 246-54 (1956). (19) Sprinson, D. B., Rittenberg, D., J . B i d . Chem. 180, 707-14 (1949). (20) Striganov, .4. R., Uspekhi F i z . S a u k 58, 365-414 (1956). (21) Stukenbroeker, G. L., Smith, D. D , Werner, G. K., McNally, J. R., Jr., J . Opt. SOC.-4m. 42, 383-6 (1952). (22) VeInberg, G. U., ZaIdel, A. N., Petrov, -4.A,, Optika i Spektroskopiya l , 972-82 119.56) (23) \T’alc‘her,-’W., Nucleonics 6, 28-36 (June 1950). (24) Werner, G. K., Smith, D. D. Ovenshine, S. J., Rudolph, 0. B., RIcNally, J. R., Jr., J . Opt. SOC.Am. 45, 202-5 11955). (25) Youden, ;:1 J., “Statistical Methods for Chemists, p. 17, Wiley, Kea, Tork, 1951. RECEIVEDfor review March 5, 1958. Accepted July 17, 1958. Work supported in.part by the U. S. htomic Energy Commission.
Spectrophotometric Determination of Microgram Quantities of Indium E. JOHNSON, M. C. LAVINE,
J.
and A. J. ROSENBERG
Lincoln laboratory, Massachusetts Institute of Technology, lexingfon, Mass.
b 5,7-Dibromo-8-quinolinol has been utilized in a colorimetric determination of indium in the microgram region. An extraordinarily linear color response with an average deviation of 0.12 y was obtained with samples containing up to 100 y of indium.
I
of studying the dissolution of indium antimonide i t became necessary t o measure 1 to 100 y of dissolved indium with a sensitivity of 0.1 y. A colorimetric method for the estimation of small amounts of indium, given by Rloeller (Z), utilizes the yellow color of the chelate compound of indium and 8-quinolinol, and yields accurate and reproducible results for 15 to 1000 y of indium. =Ittempts t o adapt AIoeller‘s proccdure to the above requirements through the use of microtechniques were unsuccessful. The reagent blank was high and unpredictable. This fact, coupled n ith a nonlinear absorbanceconcentration dependence a t low concentrations, invalidated all determinations below 2 y. The blank was reduced by preparing the indium quino5 THE COCRHE
linate as a n aqueous suspension, drying the solution in a desiccator, and leaching the product into d r y chloroform. The reproducibility of the procedure was still inadequate. I n an attempt to obtain a more reproducible system, the 5,7-dibromo derivative of 8-quinolinol was tested. In view of recent work (1, 3, 6) with 5,7dihalo-8-quinolinols , an increase in color intensity was also t o be expected. Actually, the use of 5,7-dibromo-8-quinolinol shifts the absorption maximum t o a higher wave length and the absorbance is diminished (Figure 1). Furthermore, the absorbance is a strict linear function of concentration over t h e entire range from 0 t o 100 y. The analytical procedure is simple, rapid, and relatively specific. Neutral salts inhibit the rate of color development but do not otherwise interfere. PROCEDURE
Standard indium solutions were prepared by dissolving weighed amounts of the pure metal in concentrated hydrochloric acid. A convenient concentration of stock solution is 1 mg. of indium per ml. T o obtain the calibration curve,
aliquot portions of indium solution are pipetted into 15-ml. graduated, glassstoppered centrifuge tubes, and 2.5 ml. of 0.2M potassium acid phthalate are added. The p H is adjusted to within the range 3.5 t o 4.5 using a p H meter with a suitable probe electrode, and the solution is diluted to 10 ml. with distilled water. Five milliliters of a solution containing 0.1 gram of 5,7-dibromo-8-quinolinol (recrystallized seyera1 times from absolute alcohol) in 100 ml. of reagent grade chloroform are added t o the centrifuge tube which is stoppered and shaken vigorously a t intervals over a &minute period. After brief centrifugation, samples of the chloroform layer are transferred by pipet to a 1-cm. cuvette, and the absorption is measured at 415 mp, using pure chloroform as the reference solution. The same procedure is utilized in sample analysis. With the aid of the calibration curve the weight of indium present in the sample and reagent blank may be determined. Complexing of indium by various anions, reported by Sunden ( 8 ) , may inhibit the rate of color development, in which case a more prolonged shaking time may be required. The recornVOL. 30,
NO. 12, DECEMBER 1958
0
2055
Table I. Determination of Indium by Complex Formation with 5,7-Dibromo8-quinolinol "/I=
0
Absorbance, Exptl. 0.009 0.009 0.010 0.010 0.011 0.010
0.010 0.0154
+
"/~n ,,, . 2
0.010
1
0.023 0.026
0.025
2
0.040
0.041
3
0.057
0.056
4
0.071 0.075
0.072
5
0.087 0.087
0. 087
6
0.104
0.102
7
0.121
0.118
8
0.136 0.132
0.133
9
0.151
0.148
10
0.161 0.165 0.165 0.164
0.164
20
0.318
0.318
30
0.475
0,472
40
0.630
0.626
50
0.775 0.780
0.780
80
1.244
1.241
100
1.545 1.547
1.549
11 \
RESULTS
The absorbance of the chloroform solution at 415 mp is a linear function of the indium content to at least 100 y. Table I compares the observed absorbances in a series of measurements using standard indium solutions with those calculated by the equation
ANALYTICAL CHEMISTRY
1
,
I
I
\
.\',.
\
\ '\
I \
. \ -I\L/"
!
;"
'OY
II
\\. 1
'
1,
1
"\
k---
mended time of 5 minutes of intermittent shaking is generally adequate for complete color development. A check of possible interference has shown that under the conditions used in the colorimetric estimation of indium, stannous, antimonous, ferric, aluminum, and cupric ions interfere, while arsenic, arsenous, lead, zinc, and cerium ions give no appreciable color a t the 400-7 level.
2056
=
0 360
370
380
390
400
wavE
---_____ 410
420
430
440
450
LENGTH i m p i
Figure 1. Absorbance curves for indium derivatives in chloroform
___
log Io/I
=
0.010
+ 0.154
8-Quinolinol 5,7-Dibromo-8-quinolinol
"/xn
where 71n is the indium content in micrograms of the sample. This equation was obtained by a least squares calculation from the data in Table I, giving equal weight to each measurement. The average deviation is 0.12 7 in the range of 0 to 100 y of total indium. DISCUSSION
Several authors (1, 6) have commented upon the yellow color produced in chloroform solutions of 8-quinolinol upon shaking the colorless, dry chloroform solution with water. Nasanen et al. (7) have measured the equilibrium between 8-quinolinol and its conjugate acid and base, by utilizing the absorbance maximum which occurs between 350 and 400 mp for both conjugates. This indicates that a high residual reagent color is t o be expected when using 8-quinolinol as an analytical reagent in conjunction with a hydroxylic solvent, and especially when one is not dealing with neutral solutions. Though indium oxinate has an absorbance maximum a t 395 mp, as reported by Moeller @), in practice one finds that it is but a small peak a t the toe of a large absorbance maximum which is due to the acidic conjugate of the excess 8-quinolinol. One cannot avoid this situation by reducing the concentration of 8-quinolino1, for the ex-
cess is necessary for the development of any color whatsoever. The ratio of the absorbance of the indium complex t o that of the reagent is more favorable with the dibromo derivative than with the 8-quinolinol. The nonreproducibility of the reagent blank in Moeller's method may arise from the fact that in the pH range 3.7 to 4.1 the percentage of 8-quinolinol in the chloroform layer increases by a factor of two (4). Judging from the authors' results, however, the distribution properties of 5,7-dibromo-8-quinolinol are far less sensitive to the solution conditions than those of 8-quinolinol. LITERATURE CITED
(1) Hollingshead, R. G. W., ''Oxine and Its Derivatives," Buttemorths, London, 1954-56. (2) Moeller, T., IXD.ENG.CHEM.,ANAL. ED. 15, 270 (1943). (3) Moeller, T., Cohen, A. J., Anal. Chim. Acta 4,316 (1950). (4) hfoeller, T., Pundsack, F. L., J. Am. Chem. SOC.75, 2258 (1953). (5) Ibid., 76, 617 (1954). (6) Moeller, T., Pundsack, F. L., Cohen, A. J., Ibid., 76, 2615 (1954). (7) Nasanen, R., Lumme, P., Makula, A., Acta Chem. Scand. 5, 1199 (1951). (8) Sunden, N., Suensk Kem. Tidskr. 65, 257 (1953). RECEIVEDfor review January 13, 1958. Accepted July 17, 1958. Research supported jointly by the Army, Navy, and Air Force under contract with the Massachusetts Institute of Technology.
