Table VII. Comparison of Results by Ultraviolet and Polarographic Methods
Sample 18
19 20 21 22 23 24
--Residual acrylamide, % Polarographic Ultraviolet 0.51 0.050 0.043 0.041 0.025 0.026 0.020 0.020 0.011 0.012 0.008 0.008 0.006 0.007
treated in the same manner, as the acrylamide recovery will be lowered about 10%. Any ultraviolet absorbers not separated during the extraction step or removed by the resin treatment would be expected to interfere. The presence of interfering substances can be readily detected by examination of the sample spectrum. The spectrum should be a smooth curve free of peaks and the absorbance a t 240 mp should normally be 3.0 times the absorbance at 250 mp. Data obtained by this method indicate a standard deviation of 0.003% in the 0.01 to 0.1% range. Table VI1 compares results obtained by this method with those obtained by polarography.
The ultraviolet spectrophotometric procedure is subject to the systematic errors of incomplete extraction which will yield low results, the presence of collidial matter which will cause high results if not compensated, and contamination by other ultraviolet absorbers most of which will distort the spectrum, usually in the direction of high results. ’ Choice of Method. The final choice of t h e measurement procedure is a compromise between simplicity and specificity. For samples of similar character and known interferences t h e spectrophotometric procedure is preferred. The much greater specificity of the polarographic procedures dictates the use of these procedures for samples of unknown character and as reference methods. The Difference Method can be applied directly to a sample which is found to give severe interference using the Direct Method by connecting the auxiliary circuity and adding the DDM. ACKNOWLEDGMENT
The advice and consultation furnished by R. E. Friedrich during the development of these methods is gratefully acknowledged. R. G. Beattie, R. D.
Bicknell, and K. E. Werth rendered assistance in portions of the experimental studies. LITERATURE CITED
(1) American Cyanamid Co. New Product Bulletin, Collective Volume 111, p. 27, American Cyanamid Co., New York 20, N. Y. (2) Beesing, D. W., Tyler, W. P., Kurta, D. X, Harrison, S. A., ANAL. CHEM. 21, 1073 (1949). (3) Critchfield, F. E., Funk, G. L., Johnson, J. B., Ibzd., 28,76 (1956). (4) Friedrich, R. E., Jones, G. D., Heiny, S. M., (To The Dow Chemical Co.) U. S. Patent 3,130,229 (April 21, 1964). (5) Hopke, E. H., The Dow Chemical Co., Midland, Mich., private communication, 1955. (6) Kolthoff, I. >I., Lingane, J. J., “Polarography,” Interscience, New York, 1952. (7) Ibzd., p. 374. (8),McCollister, D. D., Oyen, F., Rowe, \ . K., Tosicol. A p p l . Pharmacol., 6 (2) 172 (1964). (9) Skobets, E. >I., Nestyuk, G. S., Ukr. Khzm. Zh. 28, No. 8, 934 (1962). (10) Skobets, E. M., Nestyuk, G. S., Shapoval, V. I., Ibzd., No. 1, 72-6. (11) Skoda, W., Schura, J., Makromol. Chem. 29, 187 (1959). (12) Ungnande, H. E., Ortega, I., J . Am. Chem. Soc. 73, 1568 (1951). (13) Zuman, P., Collectzon Czech. Chem. Commun. 15, 1109 (1950). RECEIVEDfor review March 4, 1965. Accepted August 30, 1965.
Analysis of Mixtures of Aluminum, Gallium, and Indium by Solvent Extraction and Gas Chromatography GERALD P. MORIE and THOMAS R. SWEET McPherson Chemical laboratory, The Ohio State Universify, Columbus, Ohio Solvent extraction is combined with gas chromatography to produce an effective method of analysis for aluminum, gallium, and indium mixtures. The extraction of these three metals with trifluoroacetylacetone into benzene was studied. The three chelates in the organic phase are withdrawn from the extraction flasks, injected into a gas chromatograph, separated, and determined quantitatively. Aluminum, gallium, and indium were determined with a relative mean error of 2.32, 2.34, and 5.20%, respectively.
B
have been used extensively as reagents for solvent extraction of metals (18). Trifluoroacetylacetone (TFA) has been used in relatively few of-these studies. Schultz and Larsen extracted zirconium and hafnium from aqueous solutions with ETA DIKETONES
1552
0
ANALYTICAL CHEMISTRY
TFA into benzene (13). Omori et al. have studied the extraction of scandium (111) with T F A and other fl diketones (9). Recently, Scribner, Treat, Weis, and Moshier reported the extraction of several metals with TFh into chloroform (16). A TFA isobutylamine system was also used for the extraction of some divalent metals (15). The application of gas chromatography to metal chelate analysis, especially fluoroacetylacetonates has received much attention in recent years. A few quantitative studies of the synthesized chelates have been made using electron capture (10-12). flame ionization (1, 6), and thermal conductivity (14) detectors. Moshier and Sievers have summarized much of the progress in this field in a recent book ( 8 ) . The present paper describes the extraction of aluminum, gallium, and indium with T F A into benzene. The pH,
concentration of metal ion, equilibration time, and effect of diverse ions were studied. Using optimum conditions for extraction, and chromatographic conditions similar to those described by Schwarberg, Moshier, and Walsh ( 1 4 ) , accurate analyses of aluminum, gallium, and indium mixtures were performed. EXPERIMENTAL
Apparatus. An F & M model 720 gas chromatograph equipped with a thermal conductivity detector and a Brown-Honeywell recorder was used for this investigation. The chromatograph was modified by placing a piece of 4 mm. (0.d.) borosilicate glass tubing into the injection port (17 ) . Helium was used as the carrier gas and borosilicate glass columns were used throughout this work. A 50-J. Hamilton syringe with a Chaney adaptor was
used for sample injection. A model G Beckman p H meter equipped with a No. 40495 glass electrode was used for equilibrium p H measurements. Initial p H measurements were taken with a 31983 Beckman combinatlon glasssilver-silver chloride electrode. Solvent extractions were performed in A8312 Duraglass bottles with 20-400 polyseal caps (Owen-Illinois Glass Co.) . A Burrell wrist-action shaker was used to achieve equilibria in batch extractions. Quantitative radioactivity measurements were made with a R I D L model 49-54 Scaler. The detector used was a 5- x 4-inch thallium activated sodium iodide well crystal. Purity checks on each nuclide were made with a R I D L 200 channel pulse height analyzer. Reagents. All reagents were of reagent grade unless otherwise specified. Trifluoroacetylacetone was obtained from Columbia Organic Chemicals Co., Columbia, S. C. The reagent was distilled and the fraction boiling from 106-7" was collected. High purity gallium and indium metal (99.99%) were obtained from Electronic Space Products, Inc., Los Angeles, Calif. Indium-114 was obtained from Oak Ridge National Laboratory, Oak Ridge, Tenn. Gallium-68 was obtained from a bench-top gallium-68 generator made by Nuclear Science and Engineering Co., Pittsburgh, Pa. Synthesis of Aluminum Trifluoroacetylacetonate. Aluminum-TFA was used as a standard in following the solvent extraction of this metal by gas chromatography. The procedure described for the synthesis of tris(acety1acetonate) aluminum(II1) was used ( 2 ) . The chelate was purified by recrystallization from hot hexane and melted within one degree of the literature value (4). Chromatographic Columns. The column was made of 7.0-mm. (0.d.) borosilicate glass tubing, 3.5 feet in length and was bent into a helix
0
x)
Figure 1. In(III)
40
60
80
100 120 Time ( m i n u t e s )
140
160
180
xx)
Effect of time on extraction of AI(III), Ga(lll), and 0 8 X 10%
A
AI 8 x 10-~MG~ 8 X 1 O - W In
prior to filling. The column and solid support were silanized with hexamethyldisilizane according to a procedure used by Bohemen et al. (3). Silanized glass microbeads (60-80 mesh) coated, 0.5% by weight, with silicone DC-550 oil were packed into the column and it was conditioned a t 160' C. Procedure. SOLVENT EXTRACTION STUDIES. Gallium and indium solutions were prepared by dissolving the correct amount of metal in a minimum amount of hot perchloric acid in a 1-liter volumetric flask. The solutions were diluted to the mark with distilled water and transferred to 1-liter polyethylene flasks. A few drops of high specific activity tracer were added and the solutions were mixed. The weight and volume of tracer added were negligible. Aluminum solutions were made from aluminum nitrate and contained no tracer. The dependence of the extraction with respect to pH was investigated using 8 X 10-3M metal solutions. Twenty-five milliliter portions of the standard solutions were transferred to extraction bottles. The p H was ad-
justed with a few drops of 6 M HC104, 6 M NaOH, or 1M NaOH. The volume of base or acid added was recorded and used for calculating distribution ratios. Sufficient KClO, was then added if needed to bring the total ionic strength t o 0.1. Five-milliliter portions of 0.25M TFA in benzene were added and caps were immediately placed on the bottles. The bottles were then placed on a shaker and shaken a t a medium speed for 4 hours. The results of a time study, shown in Figure 1, indicated that this length of time was necessary for equilibration. Extraction flasks were then allowed to attain constant temperature in a bath a t 25' C. f 0.5'. Radiometric measurements were made as follows: Two-milliliter portions of the aqueous and organic phases were withdrawn and placed in 10-ml. screwcap vials for counting. After making background corrections, and a correction for the decay of the short lived gallium-68, the distribution ratios and per cent extraction values were calculated. Because no convenient tracer for aluminum is available, a different tech-
VOL 37, NO. 12, NOVEMBER 1965
* 1553
Table 1.
Concentration Study
Metal ion concn. ALUMINUM 8 x lO-aM 1 . 2 X 10-aM 1 . 6 x 10+M 1 . 6 x 10-*M GALLIUM
TFA concn.
Extraction, %
0.25M 0.25M 0.25M 1.OOM
99.90 85.75 71.40 93.00
0.25~ 0.251M 0.25M 1.OOM
99.90 78.50 63.45 75.15
INDIUM 0 ,25M Carrier Free 8 X lO+M 0 25M 8 x 10-4~ 0 . 2 5 ~ 8 X 10e3M 0.25M 0.25~ 1 . 2 X iO-Ziv 1 . 6 X 10d2M 0.25M 1.OOM 1 . 6 x 10-2M
99 .90 99.89 99.89 99.60 50.90 20.45 35.20
8x 1 0 - 3 ~ 1 . 2 X 10+M
1 . 6 X 10-2M 1 . 6 x 10-2M
nique was used to follow its extraction. An attempt was made to replace the T F A in the aluminum complex with 8hydroxyquinoline and determine the aluminum spectrophotometrically. However, this reaction seemed t o be quite slow in benzene so another approach was taken. Aluminum-TFA was synthesized as described above and standard solutions were prepared in benzene. Different amounts of the chelate were injected into the chromatograph, and a calibration curve based on peak area was obtained. The curve was linear and reproducible over the range investigated (1 to 4 mg. per 25 ml.). Twenty-microliter portions of the organic phase were withdrawn from the extraction flasks with a syringe and injected into the chromatograph. The Table 11.
per cent extraction was obtained from the amount of metal found and the total amount present in both phases. PREPARATION OF CALIBRATION CURVES. Because of the release of hydrogen ions from the ligand upon chelation, the initial p H was adjusted to a higher value than the equilibrium pH. I n order t o obtain a calibration curve for each metal, the initial p H of each 25-ml. aqueous phase was adjusted to a value between 7.5 and 9.5. After injection of the samples, the equilibrium p H was checked to see that it was in the range of optimum extraction. Calibration curves were made by plotting the milligrams of metal originally in the aqueous phase us. the area of the chromatographic peak. Areas were measured by using peak height times width a t half peak height for aluminum and gallium. A planimeter was used to measure the areas of indium peaks. Reproducible, linear calibration curves were obtained for each metal over the range studied. A few points on each calibration curve were repeated each day that a series of unknowns was analyzed. The curves shifted slightly because of small variations in conditions. ANALYSISOF SYNTHETICMIXTURES. Known volumes of aluminum, gallium, and indium solutions were pipetted into extraction flasks to give a total volume of 25 ml. Solutions contained from 1 to 4 mg. of aluminum, 5 to 9 mg. of gallium, and 10 to 25 mg. of indium. The total concentration of metal ions never exceeded 8 X 10-3M. Solutions were adjusted to a p H between 7.5 and 9.5 and 5-ml. portions of 0.25M T F A in benzene were added. After 4 hours shaking, the flasks were allowed to stand and 2 0 4 . samples of the organic layer were withdrawn with a syringe and injected into the chroma-
2.00
2.00 2.00 2.00 2.00
2.00
4.00 4.00 1.00 1.oo
2.00 2.00 3.00 3.00 1.oo
1.00 2.50 2.50 1554
Found, mg. 2.00 2.07 2.03 2.07 2.03 2.03 2.08 2.03 3.97 3.90 1.02 1.00 2.08 1.97
Absolute error, mg.
Rel. error,
%
Added, mg.
0.00
0.00
5.00
0.07 0.03 0.07 0.03 0.03 0.08
0.03 0.03 0.10 0.02 0.00 0.08
0.03
3.50 1.50 3.50
1.50
i.50
4.00 1.50 0.75 2.50 2.00
0.00
4.00 1.50
3.12 3.08 1.02 1.04
0.12 0.02 0.04
4.00 2.66 2.00 4.00
2.55 2.40
0.05 0.10
2.00 4.00
0.08
ANALYTICAL CHEMISTRY
RESULTS AND DISCUSSION
Solvent Extractions. The results of the solvent extractions for each metal are shown in Figure 2 . It should be pointed out t h a t t h e equilibrium p H is given on the diagrams. The equilibrium p H is lower t h a n t h e initial p H since hydrogen ions are released during extraction. Scribner has studied the extraction of aluminum with TFA into chloroform (16). Greater than 98% of the aluminum was extracted in the presence of acetate buffer from p H 4 to 7 . The extraction of the other two metals has not been studied before with TFA. The present study was performed using benzene as the solvent so that the electron capture detector could also be used. The concentration of one of these metals (indium) was reduced to determine whether the extraction is applicable to extremely small amounts. As expected, nearly complete extraction resulted all the way down to carrier free indium-114m. The results for this and for the upper concentration limits of all three metals are shown in Table I. Morrison and Freiser have pointed out ( 7 ) that the stability of metal chelates usually varies inversely with the acidity constant of the ligand, while the reagent anion concentration at a given p H is higher for more acidic
Analysis of Aluminum, Gallium, and Indium Mixtures
Aluminum
Added, mg. 2.00 2.00
tograph. The equilibrium p H of the solutions should be 4.5 to 5.5. If emulsion formation occurred during equilibration, the extraction bottles were centrifuged before a sample was taken for gas chromatographic analysis. The chromatographic column was maintained at 128' C.
5.00 5.00 5.00 7.50' 7 50 7 50 7 50 5 00 5.00 8.50
8.50
Gallium Absolute Found, error, mg. mg. 5.12 0.12 5.05 0.05 5.00 0.00 5.20 0.20 7.70 0.20 7 80 0 30 7 60 0 10 7 70 0 20 4 90 0 10 4.93 0.07 8.30 0.20 8.30 0.20
Rel. error,
% 2.40 1.00 0.00
4.00 2.67 4 00 1 33 2 67 2 00 1.40 3.15 3.15
5.00 5.00 5.00
5.00
5.04 5.05 5.20 5.05
0.04 0.05 0.20
0.80 1.00 4.00
9.00 9.00
9.20 9.30
0.20 0.30
2.22 3.33
6.00 6.00
5.80 5.80
0.20 0.20
3.33 3.33
0.05
1.00
Added, mg. 10.0 10.0 10.0 10.0
Indium Absolute Found, error, mg. mg. 9.0 1,oo 9.5 0.50 9.75 0.25 10.5 0.50
Rel. error,
%
10.0
5.00 2.50 5.00
15.00 15.00
14.50 14.25
0.50 0.75
3.00 5.00
17.50 17.50
16.50 16.50
1.00
1.00
5.70 5.70
25.00 25.00
23.75 23.75
1.25 1.25
5.00 5.00
reagents. The latter is usually more important and extraction occurs at a lower p H for more acidic reagents. This is observed in TFA extractions as compared to acetylacetone (f 9). The extraction of thallium(II1) from aqueous solution was also investigated. Only a very small amount of thallium could be extracted, probably because spontaneous reduction to thallium (I) occurs. Aloeller has stated in an oxine extraction study of thallium(III), that some additional complexing agent would appear to be essential for the extraction of this ion (6). Thallium(1) was also investigated but hardly any extraction occurred in the p H range of optimum extraction for the other three metals. Analysis of Synthetic Mixtures. A series of eight extractions each containing 2.0 mg. of aluminum, 5.0 mg. of gallium, and 10.0 mg. of indium in 25 ml. followed by chromatographic separation and determination was checked for precision. T h e relative standard deviation was 1.9870, 2.4870, and 5.21% for aluminum, gallium, and indium, respectively. The precision of t h e chromatographic procedure alone was checked by making a series of 10 injections from one of the aluminum extractions. The relative standard deviation was 1.03’% for 3.0 mg. of aluminum in 25 ml. The chromatogram for the separation is shown in Figure 3. The results for a series of synthetic unknowns are given in Table 11. The mean relative error was 2.32%, 2.34%,
O.!
*
.)
0
2
.
E
* E
“*
L
Figure 3. Separation of AI(TFA)3, Ga(TFA)3,and In(TFA)3 by gas chromatography Column temperature, 128Oc.i flow rate, 80 cc./rnin.; injection port tern’ perature, 135OC.; detector temperature, 1 5OoC.
and 5.20% for aluminum, gallium, and indium, respectively. The entire method was checked for interferences by various ions. The results of this study are given in Table 111. The amount of metal listed in Table I1 was always present in 25 ml. of aqueous solution. It would be possible to obtain greater sensitivity if larger ratios of aqueous volume to organic volume were used. Moreover, recent studies in which a n electron capture detector was used (10-12) indicate that a n extraction followed by a determination using this detector would be extremely sensitive.
Table 111. Effect of Diverse Ions (2.00 mg. of aluminum, 5.00 mg. of gallium, 10.0 mg. of indium) hIolar ratio Relative error, 70 diverse Added, ion/Ga A1 Ga In Species mg. 2.67 2.50 100 4.00 381 c12.00 1.66 3.50 100 666 NO3 4.10 3.50 3.00 1052 100 S04-2 4.33 100 5.50 5.00 644 Acetate 25 2.15 3.20 4.00 a a a 100 1630 Tartrate a a 25 407 10 2.50 a 163 h Ni f 2 100 630 ... ... a 5.00 25 157 10 2.80 4.00 3.50 63 b 100 ... ... c u +2 682 21.40 c 25 170 c a ... 10 68 b 100 Go +2 ... 633 158 25 3.50 10.0 12:50 10 63 1.50 2.00 3.15 b Cr + 3 100 ... ... 558 3.50 E 6.80 140 25 10 56 2i50 3.00 3.50 bIn +2 I00 ... ... 590 b 25 ... 147 59 10 2.50 5.00 9.50 b Zn +z 702 100 ... ... 2.50 175 25 3.10 3.75 a Very little extraction occurred. * Emulsion formation. c Peak unresolved from Ga peak. (I
(1
G
. I .
ACKNOWLEDGMENT
The authors gratefully acknowledge the sample of gallium-68 contributed by W. G. Myers and the helpful discussions with R. E. Sievers. LITERATURE CITED
(1) Albert, D. K., ANAL.CHEM.36, 2034
11964). (2) Arch, A., Young, R. C., Inorg. Syn. 2,17 (1946). (3) Bohemen, J., Langer, S. H., Perrett, R. H., Purnell, J. H., J . Chem. SOC. 1960, 2444. (4) Fay, R. C., Piper, T. S., J. Am. Chem. SOC.85, 500 (1963). (5) Hill, R. D., Gesser, H., J . Gus Chromatog. 1, 10 (1963). (6) Moeller, T., Cohen, A. J., ANAL. CHEM.22,686 (1950). (7) Morrison, G. H., Freiser, H., “Solvent Extraction in Analytical Chemistry,” p. 27, Wiley, New York, 1957. (8) Moshier, R. W., Sieven, R. E., “Gas Chromatography of Metal Chelates,” Pergamon Press, Oxford, in press, (1965). (9) Omori, T., Wakahayashi, T., Oki, S., Suzuki, N., J . Inorg. Nucl. Chem. 26, 2265 (1964). (10) Ross, W. D., ANAL. CHEM.35, 1596 (1963). (11) ROSS,W. D., Sievers, R. E., Wheeler, G., Ibid., 37,598 (1965). (12) Ross, W. D., Wheeler, G., Ibid., 36, 266 (1964). (13) Schultz, B. G., Larsen, E. M., J . Am. Chem. SOC.72,3610 (1950). (14)Schwarberg, J. E., Moshier, R. W., Walsh, J. H., Tahnta 11, 1213 (1964). (15) Scribner, W. G., Kotecki. A. M., ANAL.CHEM.37, 1304 (1965).’ (16) Scribner, W. G., Treat, W. J., Weis, J. D.. bloshier. R. W.. Ibid.. D. 1136. (17) Sievere., R. E., 17th Annl‘al Summer Symposium, ACS, Division of Analytical Chemistry, Tucson, Ariz., June 1963. (18) Stary, J., “The,,Solvent Extraction of Metal Chelates, Pergamon Pre‘ss, New York, 1964. (19) Stary, J., Hladky, E., Anal. Chim. Acta 28, 227 (1963). RECEIVEDfor review April 29, 1965. Accepted August 23, 1965. VOL. 37, NO. 12, NOVEMBER 1965
1555
