Pa rt it io n C:hro mato gra phic Se pa ratio n a nd Determination of cis- and trans-l,3Cyclopentlanedicarboxylic Acids E. CAROL BOSSERT, AUDREY DONMOYER, ROBERT D. HINKEL,' and ROBERT MAlNlER Research Department, Koppers Co., Inc., Monroeville, f a .
b A partition chromatographic method has been developed fcr the separation and quantitative determination of cisand frans-l,3-cyclop1~ntanedicarboxylic acids in crude products derived from the oxidation of norbornylene. This procedure determines 40 to 100% total 1,3 - cyclopentanedicarboxylic acid in the presence c'f impurities. A silicic acid-water mixture was employed as the stationary phase, while a gradient mixture of tert-butyl alcohol and chloroform constitiJted the mobile phase. Quantitative (analyses having a precision of about :4=27& were obtained by titrating one half of each eluate fraction with alcoholic potassium hydroxide. The cis and trans isomer regions were characterized by melting point determinations of the evaporated residues from the remaining halves of the eluate fractions.
I
THE COURSE of preparing 1,3cyclopentanedicarbo tylic acid, a method was needed for the quantitative determination of its cis and trans isomers. A literature survey disclosed several modifications of the partition chromatographic method developed by Marvel and Rands (7') f x the separation of certain straight-ch:iin dicarboxylic acids. Similar procedures utilizing water on silicic acid a3 the stationary phase and butanol-chloroform solutions as the mobile phases were reported by Higuchi, Hill, and Corcoran ( 5 ) , Corcoran (4))Smith (Q), and Smith (10). A method for the separation of cyclic compounds, including I-yclobutane and cyclopentane derivatives, was also published by Baldwin, Loeblich, and Lawrence ( 2 ) . After preliminary investigations, a set of optimum conditions was established for the chromatographic separation of cis- and trans-1,3-cyclopentanedicarboxylic acid. These conditions are used in the quantitathe determination of crude 1,3-cyclopentanedicarboxylic acid.
K
A 3.5 volume 7, tert-butyl alcohol in chloroform solution of the acid sample is separated on a co1u)nn of 100-mesh Present address, Greensburg Branch, University of Pittsburgh Greensburg, Pa
silicic acid powder containing 44.3 weight yo water. The eluent is a gradient solvent mixture varying in composition from 3.5 to 8 volume % tertbutyl alcohol in chloroform. The total eluate volume is 400 ml., and the flow rate is maintained constant a t 0.8 ml. per minute. A portion of each eluate fraction is evaporated to dryness. The melting point of the residue after drying is used to identify the cis and trans isomer regions. A second portion of each fraction is titrated with standard alcoholic potassium hydroxide. The amount of cis or trans isomer is calculated from the cumulated titers of the respective fractions. EXPERIMENTAL
Chromatographic column, borosilicate glass tubing, 22-mm. inside diameter, 38 cm. long with 35,'25 standard ball ground-glaqs joint and 2-mm. bore straight Teflon stopcock. Gradient elution apparatus [see Figure 1 and (1) for details of construction]. The mixing reservoir is provided with a magnetic stirrer and stirring bar. Melting point apparatus, improved Fisher-Johns with microcover glasses. Silicic acid, Mallinckrodt analytical reagent grade, IOO-mesh, "suitable for chromatographic analysis by the method of Ramsey and Patterson'' ( 8 ) . Apparatus and Reagents.
Procedure.
PREPARATIOS
OF
SILICICACID. T o ensure uniform column operation over a n evtended
u-
Figure 1 .
8-mm. 0. D.
Gradient elution apparatus
period of time, prepare a single large batch of adsorbent from several 1pound lots of reagent, making certain t h a t t h e silicic acid is thoroughly mixed before sampling. Determine the water content of the silicic acid by drying a test amount a t 110" C. in a n oven for 1 hour and then heating it a t 800" C. for an additional hour in a muffle furnace. The preliminary drying at 110" C. is necessary to avoid loss of sample by spattering. Calculate the volume of water and quantity of silicic acid that must be mixed together to obtain a mixture containing 44.3 weight % water and 55.7% silicic acid and having a total weight of 90 grams. Thoroughly mix the calculated quantities of silicic acid and water in a 500-ml. Erlenmeyer flask until the mixture is a homogeneous powder. Stopper the flask, shake the mixture vigorously for 1 minute, and allow the powder to settle to the bottom of the flask. Slowly add 300 ml. of 3.5 volume % tert-butyl alcohol in chloroform to the wetted silicic acid powder, and intermittently stir the mixture until a fine slurry is obtained.
PREPARATION OF CHROMATOGRAPHIC COLUMN. Insert a small cotton plug a t the bottom of the column before filling. Add the silicic acid slurry sloivly while simultaneously stirring the mixture with a long rod until all air bubbles disappear. After transferring the slurry into the column, slowly remove the rod with constant stirring to free air bubbles and ensure homogeneity of the slurry. As soon as the top of the column becomes firm, slowly add 100 ml. of 3.5 volume 7 , tert-butyl alcohol in chloroform to the top of the column, being careful not to disturb the smooth surface of the packing. Drain the excess tert-butyl alcohol in chloroform solution to the top of the packing before introducing a sample. PREPARATIOK OF APPARATUS AND SAMPLE.Add 200 ml. of 3.5 volume % tert-butyl alcohol solution to the mixing reservoir of the gradient elution apparatus (Figure 1) and 200 ml. of 8 volume % tert-butyl alcohol in chloroform solution to the storage reservoir. Melt the sample if it is a solid mass rather than a fine powder. Then weigh approximately 0.6 gram of acid sample (to the nearest 0.1 mg.) into a 10-ml. volumetric flask. Dilute to volume with 3.5 volume o/o tert-butyl alcohol in chloroform solution to dissolve, and shake I\ cll to ensure thorough mixing, VOL. 36, NO. 7, JUNE 1964
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I t is sometimes necessary to dissolve the acid in 0.35 ml. of tert-butyl alcohol and then to dilute to 10 ml. with chloroform. ANALYSIS OF SAMPLE. Carefully pipet a 1-ml. aliquot of the acid solution dropwise onto the top of the wetted silicic acid column. When the solution has drained to the top of the silicic acid, open the stopcock between the two reservoirs of the gradient elution apparatus, allowing the solutions to mix with continuous mechanical stirring in the mixing reservoir. Adjust the stopcocks controlling the flow of solvent into the column and eluent from the column so that a flow rate of 0.8 ml. per minute is maintained. The liquid level should remain about inch above the level of the silicic acid packing. Collect 44 10-ml. fractions in volumetric flasks. The cis and trans isomers are not eluted in the first 200 ml. of eluate. Therefore a composite eluate fraction of 200 ml. may be collected and discarded if only the cis and trans isomers are to be determined; however, other acidic constituents may be present in the initial fractions. Pipet a 5-ml. aliquot from each fraction into a 10-ml. Erlenmeyer flask, add one drop of 0.1 weight % per volume m-cresol purple indicator in ethanol, and titrate each fraction with 0.05N alcoholic potassium hydroxide. Transfer the remainder of each fraction to a 30-ml. evaporating dish, and evaporate the solution to dryness on a steam bath. Measure the melting point of each residue by use of a Fisher-Johns melting point apparatus. Fractions having melting points from 120" to 123" C. are the cis acid, while fractions having melting points from 98" to 99" C. are the trans acid. The amount of cis or trans isomer may be calculated from the cumulative titers of the respective isomer fractions. DISCUSSION
Melting Point Calibration. To characterize the purity of the 1,3cyclopentanedicarboxylic acid fractions recovered in the chromatographic separations, melting points were determined. Occasionally a fraction, eluted between the cis and trans isomers, had a melting point range from 86" to 120' C. 'To determine whether these low melting points were due to a n impurity present in the sample that had eluted with the isomers or a mixture of the two acids caused by incomplete separation, melting points of mixtures containing different percentages of the cis- and trans-1,3-cyclopentanedicarboxylic acids were measured. A melting point curve (Figure 2) reaches a minimum of 85' to 88' C. a t a concentration of 69 weight % tran.s-1,3-cyclopentanedicarboxylic acid and 31 weight yocis-1,3-cyclopentanedicarboxylic acid. It was therefore concluded that fractions having a melting point range between 86" and 120' C. were mixtures of the two isomers. The relative amounts of each isomer may be determined from the curve.
12 14
ANALYTICAL CHEMISTRY
130
FIGURE 2 MELTING RANGE FOR MIXTURES OF CIS-and
I
5b
do
Ib 20 30 20 60 70 so WEIGHT PER CENT TRANS- I, 3-CYCLOPENTANEDICARBOXYLIC ACID
Column Operation. ; i number of chromatographic separations were made t o determine the effect of different variables in the separation. Preliminary analyses were conducted with silicic acid columns containing 44.394 water as the stationary phase. Subsequent attempts to improve the separation of the cis and trans isomers of 1,3-cyclopentaned1carboxylic acid were made by altering this phase. N o significant improvement in resolution was obtained by increasing the acidity of the stationary phase as reported by Isherwood (6) or the alkalinity as recommended by S'andenheuvel and Hayes ( 2 1 ) . Furthermore, attempts to buffer the column with 1 M (pH 5.40) citrate buffer used as the stationary phase (5, 10) or 2-14 glycine solution on silicic acid adjusted to a pH of 8 with concentrated sodium hydroxide (4), failed to effect a sharper separation of the isomers. lJ3-Cyclopentanedicarboxylic acid was not recovered on a column of silicic acid mixed with ammonia and water as described by Ramsey and Patterson (8). A qualitative method of acid detection employing m-cresol purple as an internal indicator (9) was also abandoned in favor of a more systematic method for determining the components of the eluate fractions by titration. Initial chromatographic separations were carried out having mobile phases of n-butyl alcohol in chloroform. However, the crude acid samples decreased in acidity upon standing. To minimize the possibility of the acid samples' undergoing esterification during the slow passage through the column ( 5 ) , all subsequent separations were conducted with tert-butyl alcohol in chloroform solutions as the mobile phase. Separations using an elution scheme of 2 volume yo tert-butyl alcohol in chloroform followed by 5 volume % tert-butyl alcohol in chloroform separated the cyclopentanedicarboxylic
IiO
acid from other impurities in crude samples. However, the cis and trans isomers were not separated. Since attempts to improve separation of the cis and trans isomers by varying the concentration of the eluting solvents were not successful, a qystem was set up for gradient analysis in which the tertbutyl alcohol-chloroform ratio was increased continuously and linearly. Initial evperiments were conducted 1%ith a gradient solvent mixture varying in composition from 1 to 8 volume % tert-butyl alcohol in chloroform. I n an attempt to decrease the time for an over-all analysis, the starting tert-butyl alcohol composition of the gradient mixture was increased. Additional experiments were conducted with gradient mixtures of 3.5 to 8, 4 to 8, and 5 to 8 volume % mixtures of tertbutyl alcohol in chloroform. Since the use of these compositions, in effect, decreases the rate of change of tert-butyl alcohol concentration in the eluent, it permits a better resolution of the cis region. At the same time, the higher starting alcohol concentration causes the cis and trans acids to move more rapidly through the column. The optimum rate seems to exist with the starting 3.5 volume % concentration, where the leading trans fractions are not appreciably pushed into any sample impurities that may have eluted just ahead of this isomer. Original experiments were made using a flow rate of 2 ml. per minute. Lowering the flow rate effected a better separation of the cis and trans acids; however, no improved separation could be observed a t a flow rate of less than 0.8 ml. per minute. h comparison of analyses conducted on silicic acid columns averaging 12.6 to 40.0 em. in length revealed that the 40-em. column resulted in marked improvement in separation. Columns longer than 40.0 cm., which would increase the time of analysis, were not tried, since separations were adequate using the 40.0-cm. column.
:!OW
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sample; the second, 9.5 weight Yo. To characterize further the identity of the substances separated, infrared spectra were obtained of mineral oil mulls of the isolated dried acid fractions. The suspected trans fractions exhibited qualitatively similar spectra, except for some significant variations in band shapes and intensities in the 7- to 8- and 10- to 15-micron regions (Figure 5 for irans fraction 33) ; the cis fractions, however, exhibited absorption identical to that of the ,is standard. The spectra of trans fractions could be changed and made to appear identical by the addition of suitable amounts of water (Figure 6). Examination of various wetted residues indicated that the variations observed in the original spectra must be due to the presence of varying amounts of water, which apparently lead to variable amounts of hydrate formation. Since the trans fractions, by titration, comprised about 90 weight yo of the original sample, their spectra should be similar to those of the starting material shown in Figure 7 . However, neither the wet nor the dry forms of the fraction residues showed any agreement with the original. Furthermore, the addition of water to some of the original sample did not produce a sample having a spectrum similar to that observed for the fractions. Such behavior led to the belief that the 10 % of cis acid present in the original sample may have caused some
700
1
WAVELENGTH (MICRONS)
Figure
3. Infraiped spectrum of cis- 1,3-cyclopentanedicarboxylic acid I-
3s
7I
8
5
b? m ?
El 6 8
6 1
t; a t:
;4
-?
/-SOLVENT / COMPOSITION
d
I 0
/'
f 5-
cn' z 0
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/
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-6
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I
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-
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-
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Figure 4. Chromatographic separation of trans 1,3 - cyclopentane dicarboxylic acid
8 J
4
500 CUMULATIVE VOLUME OF ELUATE FRACTIONS,
Nature of cis- and trans-l,3-Cyclopentanedicarboxylic Acids. Cassidy (3) reported that a pure cis compound may be altered to a mixture of cis and trans isomers and. yield two zones. I n view of this information, the reference acids provided by synthesis were analyzed chroniatographically to test for the occurrence of this phenomenon and simultaneously to determine the purity of the reference materials, A portion of the cis acid standard was chromatographed on a silicic acid column and eluted at' a flow7 rate of 0.8 ml. per minute with a gradient mixture varying in composition from 1 to 8 volume % tert-butyl alcohol in chloroform. (As ;mentioned before, this gradient mixture was used for preliminary chromatographic separations.) Recovery of cis-l13-cyclopentanedicarboxylic acid, as determined by titration of each fraction with alcoholic potassium hydroxide, was 100.8 % of theoretical with no trace of the trans isomer. The infrared spectra of the eluted fractions were found to be identical to the spectrum of the cis acid standard, shown in Figure 3. Cont,rary to the above results, the elution curve for the trans acid standard (Figure 4) showed two well separated groups of fractions i,hat appeared to correspond t'o the trans and cis isomers, respectively. The first group represented 92.2 weight 70 of the
ml.
40063000 100
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WAVELENGTH (MICRONS)
Figure 5. infrared spectrum of trans- 1,3-cyclopentanedicarboxylic acid, chromatographic fraction 33
WAVELENGTH (MICRONS)
Figure 6. Infrared spectrum of trans- 1,3-cyclopentanedicarboxylic acid, chromatographic fraction 33 with water added VOL. 36, NO. 7 , JUNE 1964
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Figure 7. Infrared spectrum of trans- 1,3-cyclopentanedicarboxylic acid sample containing 10% cis- 1,3-cyclopsntanedicarboxylic acid
4OOO3000
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IS00
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WAVELENGTH (MICRONS)
Figure 8. Infrared spectrum of synthetic mixture of 10% cis- and trans-1,3-cyclopentanedicarboxylic acid
interaction, preventing hydrate formation with the material separated in these fractions. This hypothesis was tested by obtaining the infrared spectrum of an approximate 10/90 weight % mixture of the standard cis acid and one of the sample trans fractions (Figure 8 ) and comparing it to the spectrum of the reference trans acid. The two spectra were identical, and the addition of water to the mixture, like the standard trans isomer, produced no change in its spectrum. These experiments on the trans acid standard, together with the information reported previously for the cis standard, indicate that these isomers are not decomposed or rearranged
90%
during the course of the chromatographic analysis. It is not probable that the other components of a crude 1,3cyclopentanedicarboxylic acid sample promote such decompositions or rearrangements. Analysis of Synthetic Mixtures. To establish the validity of the method, a synthetic mixture of the reference isomers was separated under conditions similar to those used to analyze the
reference acids. The elution curve (Figure 9) shows two sharply resolved group; of fractions. The first group, upon evaporation to dryness, gave residues having narrow melting point ranges, all of which were within 96" to 99" C. and appeared to correspond to the values for the trans isomers. The infrared spectra of these same fractions corresponded to the spectrum previously obtained for the trans fractions of the trans acid standard. The second group of fractions yielded residues having melting points and infrared spectra which compared very closely with those of the cis standard. The composition of the synthetic mixture is listed in Table I along with the experimental data obtained for the mixture. The basic method described here has been used successfully for the quantitative Separation and determination of the cis and trans isomers of 1,3-cyclopentanedicarboxylic acid in crude samples in the form of either the free acid or the amine salt. Impurities such as formic acid, hydrochloric acid, 1,3cyclopentanedicarboxaldehyde, monomethyl norcamphorate, and dimethyl norcamphorate elute before the acid and do not interfere. An overall comparison of the data indicates that the separations obtained are reproducible, both with respect to the manner of elution and the quantities of acid determined. It is estimated that, under ordinary conditions, a precison of +2y0 may be expected. ACKNOWLEDGMENT
The authors express their appreciation to the Koppers Co., Inc., for permission to publish this work, and to S. C. Temin and M. E. Baum of the Polymer Chemistry Group for suggestions initiating this investigation and preparation of standards.
Table I. Analysis of a Synthetic Mixture of cis- and frans-1,3-Cyclopentanedicarboxylic Acid
Component cis-l,3-Cyclopentanedicarboxylic acid trans-l,3-Cyclopentanedicarboxylic acid
Weight yo ReAddeda covered 75 1
i3 9
24 9
26 1
a Correction made for amount of cis1,3-cyclopentanedicarboxylicacid in trans acid standard used to prepare mixture.
1 2 16
ANALYTICAL CHEMISTRY
CUMULATIVE VOLUME OF ELUATE FRACTIONS, ml. Figurt 9. Chromatographic separation of cis- and trans- i,3-cyclopentanedicarboxylic acid
LITERATURE (CITED
( 1 ) Back, R. M., Ling, S.-S., ANAL. CHEM.26, 1543-6 (1984). ( 2 ) Baldwin, D. E . , Loeblich, V. M., Lawrence, R . V., Jbzd., pp. 760-2 (1954). ( 3 ) Cassidy, H . C., “Fundamentals of Chromatography,” in “Technique of Organic Chemistry,” Vol. X, p . 283,
Interscience, Xew York-London, 1957. ( 4 ) Corcoran, G. B., ANAL. CHEM.28, 168-71 (1956). ( 5 ) Higuchi, T., Hill, N. C., Corcoran, G . B., Ibid., 24,491-3 (1952). ( 6 ) Isherwood, F. A., Biochem. J . 40, 688-95 (1946). ( 7 ) Marvel, C. J., Rands, R. TI.,J . Am. Chem. SOC.72,2642 (1950). ( 8 ) Ramsey, L. L., Patterson, W. I.,
J . Assoc. O$c. Agr. Chemists 31, 139-50 (1948). ( 9 ) Smith, A. I., ANAL.CHEM.31,1621-24 (1959). (10) Smith, E. D . , Ibid., 32, 1301-4 (1960). ( 1 1 ) Vandenheuvel, F. A., Hayes, E. R., Ibid., 24, 960-5 (1952). RECEIVEDfor review December 16, 1963. Accepted March 16, 1964.
Separation of Scandium from Yttrium, Lanthanum, and the Rare Earths by Cation Exchange Chromatography F. W.
E. STRELOW
and C. J. C. BOTHMA
National Chemical Research laboratory, South African Council for Scientific and lndustrial Research, Pretoria, South Africa
b Scandium is separated from yttrium, lanthanum, cerium, scimarium, erbium, and ytterbium b y cation exchange chromatography. The scandium is eluted from a column of A G 5 0 W - X 8 resin with 2N sulfuric: acid while the rare earths are retciined. The rare earths can then b e eluted with 4 N hydrochloric acid. Results of quantitative separations are reported for two different column size!;: 0.377 mg. of scandium could b e separated quantitatively from 443.6 mg. of lanthanum or from 288.4 mg. of ytterbium, and 150.8 mg. of scandium from 0.887 mg. of lanthanum. Flow rates are critical, especially .For the smaller columns. The procedure should also separate scandium from the rare earths not named above.
I
N RECENT YEARS, various procedures
applying ion exchange chromatography for the separaiion of scandium from the rare earth elements have been described. Radhakrishna (11) separated scandium from yttrium and lanthanum using a column of Amberlite IR-100H cation exchange resin and a citrate eluent. The wandium, which is eluted first, shows a strong tailing effect. Iya investigated the cation exchange separation of scandium from the rare earths in citrate ( 7 ) and E D T A (8) media, and Vickery (16) employed EDTA and hydrazinl. diacetic acid as eluents. Again strong tailing effects were observed and thfl separations were not quite quantitative. Fritz and Umbreit (3) separated scandium and yttrium using a Dowex 50-X4 cation exchange column. The ions were complexed with E D T A before adsorption and eluted with EDTA solutions of definite p H valueq. Quantitative separations of scar dium from the other rare earths are suggested by ion retention against pH curves given in their paper. Spedding et al. (IS) separated
scandium from the rare earths on cation exchange columns using HEDTA and Cu-EDTA as complesing agents. Minczewski and Dybczynski (10) investigated the anion exchange behavior of the EDTA complexes of scandium and the rare earths and found that separation of scandium from some rare earths was possible but from others, especially from thulium, ytterbium, and lutecium, was improbable. Rezanka et al. (12) separated scandium from lanthanum on a Katex S cation exchange resin using a lactate eluent. James, Powell, and Spedding (9) found that scandium is eluted before the rare earths from Amberlite IR-120 cation exchange resin using EDTA as eluent. KO results of separations are given. Hamagushi et al. (4, 5 ) investigated the separation of scandium from a number of elements using Diaion SK-1 cation exchange resin and HCI-NHa SCN mixtures as eluents. The separation of scandium from dysprosium and europium does not seem to be satisfactory and the heavier rare earths are not separated at all. A separation of scandium from yttrium and the lanthanides using a strongly basic anipn exchange resin and 13N HCl as eluent has been described by Hamagushi, Kuroda, and Shimizu (6) and by Yoshimura, Takashima, and Waki (17’). The value of this separation appears to be somewhat doubtful because the distribution coefficient for scandium is very low, even at 135 HC1. Only small amounts of scandium can be absorbed ( < 3 mg. of Sc203) and an early break-through occurs. Furthermore, practical difficulties are encountered in handling the high HC1 concentration. Faris and Warton ( 2 ) investigated the ion exchange behavior of scandium, yttrium, and the rare earths in nitric acid-methanol mixtures using Dowex I and Amberlite CG-400 resin in the nitrate form. He presented distribution coefficients as a function of nitric acid
and of methanol concentrations, as well as separation factors relative t o gadolinium. The values of the distribution coefficients suggest that it should be possible to separate scandium from the rare earths by this procedure, provided that the exchange reaction rates are not slowed down too much by the presence of the organic reagent. KO data on actual separations are given in the paper. Faris ( I ) also investigated the absorption of scandium fluoride complexes on anion exchange resins. Most of the above procedures make use of organic complexing agents which introduce complications into the determinations or into further separations which may be carried out on the eluates. I n addition, quite a number of the procedures do not seem to provide satisfactorily quantitative separations for accurate analytical work. The introduction of a fairly simple eluent able to separate scandium quantitatively from the rare earths, therefore, seems to have its attractions. .4 s>sternatic survey (15 ) of equilibrium distribution coefficients of cations in sulfuric acid using Bio-Rad AG 50W-X8 resin was undertaken in this laboratory and suggested that it should be possible to separate scandium quantitatively from yttrium and the rare earths by elution with about 2A‘ H2S04. At 2.V acid, the distribution coefficient for scandium is 8.5 and the separation factors are cusc-~&= 32.3, ag,-y = 5.8, crgc-yb = 5.6. EXPERIMENTAL
Reagents and Apparatus. Analytical reagent grade chemicals were used whenever possible. Scandium oxide and rare earth oxides of 99.9% purity were obtained from L. Light and Co., England. T h e xylenol orange was supplied by E. Gurr, Ltd., London. Standard solutions containing 5 meq. of the cation per 20 ml. in 0.1S sulfuric acid were prepared and standardized titrimetrically with EDTA VOL. 36, NO. 7, JUNE 1964
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