Distribution Studies between Thenoyltrifluoroacetone (TTA) in Methyl Isobutyl Ketone (MIBK) and Aqueous Solutions Using Radiotracers of Group II and Group 111 Elements W. Morrison Jackson,‘ Geoffrey I. Gleason, and Percy J. Hammons, Jr. Special Training Division, Oak Ridge Associated Universities, Oak Ridge, Tenn.
Using a procedure designed to yield distribution coefficients which can be quantitatively compared, 13 Group II and Group Ill elements were studied. Under standard conditions a radiotracer of the element of interest was distributed between an a ueous phase and an organic phase consisting of O.1MCfTA in MIBK. The distribution coefficients were computed from the ratio of activity in the organic phase to that in the aqueous phase. By varying the pH of the aqueous phase, distribution coefficients within the range of 10-3 to 103 were obtained. From the data, pH conditions can be selected to give single stage separation factors of 1000 or greater between the following element pairs: Ca-Sc, Ca-Y, Ca-La, Zn-Sc, Sr-Sc, Sr-Y, Sr-La, Cd-Sc, Cd-Y, Cd-In,. Cd-La, Ba-Sc, Ba-Y, Ba-La, Sc-Y, Sc-In, Sc-La, Sc-TI, Y-TI, In-TI, and La-TI. (Parentdaughter radioisotope pairs are underlined.) Certain system limitations were found for beryllium, gallium, and mercury.
-
THE USE OF TTA as a reagent for solvent extraction is well established in analytical chemistry. Its ability t o extract metal ions from stronger acid solutions than most other chelating agents, thus avoiding interference from hydrolysis, makes it applicable to most of the metallic elements. A summary of the studies through 1960 by Poskamzer and Foreman ( I ) showed that most investigators used benzene as the solvent for TTA. A few studies indicated enhanced extraction of certain elements when MIBK was used as the organic solvent (2-4). Later studies by Crowther and Moore (5) proved that MIBK retarded the decomposition of TTA when the pH of the aqueous contacting solution was basic. Using MIBK as the solvent for TTA, Akaza (6) studied the extraction of magnesium, calcium, strontium, and barium over a wide pH range using atomic absorption for the measurement of the concentrations. The objective of these studies was to determine the distribution of Group I1 and Group I11 elements between aqueous and TTA-MIBK solutions under standard conditions, so that the feasibility of separating two or more elements can be concluded from a comparison of their distribution coefficient curves. This information should be of particular interest to the radiochemist, because of the three radioisotope parent-daughter pairs, gOSr-VoY, 11sCd-1151n,and 14OBa-*4oLa, as well as to 1
Present address, Alabama Power Co., Birmingham, Ala.
(1) A. M. Poskamzer and B. M. Foreman, Jr., J. Inorg. Nucl. Chem., 16, 323 (1961). (2) J. R. Thomas, H. W. Crandall, T. E. Hicks, B. Rubin, and J. Soldick, USAEC Report No. KLX-44, Kellex Corp., New York, N. Y. (April 29, 1949). (3) D. L. Heisig and H. W. Crandall, USAEC Report No. UCRG 764. Universitv of California. Radiation Lab., Berkeley. Calif. (June 30, 195oj. (4) T. Kiba and S. Mizukami, Bull. Chem. SOC.Jup., 31, 1007 (1958). ( 5 ) P. Crowther and F. L. Moore, ANAL.CHEM., 35, 2081 (1963). (6) I. Akaza, Bull. Chem. SOC.Jup., 39,971 (1966).
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0
the chemist who is interested in the separation of elements within the two groups. EXPERIMENTAL
Apparatus. A Burrell “Wrist-Action Shaker,” Model BB, was used for equilibration of samples. For gamma counting, a 2-inch NaI(T1) detector shielded with 1 inch of lead was used in combination with a single channel analyzer. For beta counting, a Beckman “Liquid Scintillation System,” Model LS-100, was used. Reagents. ORGANICSOLUTIONS.Thenoyltrifluoroacetone (TTA) supplied by Columbia Organic Chemicals Co. was dissolved in methyl isobutyl ketone (MIBK) to make 0.1M solutions. TRACER STOCKSOLUTIONS.The radioisotopes, l 33Ba, 45Ca, ‘@La, s5Sr, ssY, and 65Zn in HC1; 115Cd-11SIn , 2oaHg, and 204Tlin “ 0 3 were obtained from the Nuclear Division, International Chemical and Nuclear Corp. The radioisotopes 7Be, lI4mIn, and 4 e S in ~ HC1 were obtained from the Amersham/Searle Corp. Gallium-67 in HCl was obtained from the Oak Ridge National Laboratory. AQUEOUS TRACERSOLUTIONS.For chloride solutions, pH of 1 or above, the stock tracer solutions were diluted with 0.1N HC1 until a 2-ml sample placed directly on the NaI crystal housing gave a gamma count rate of about 100,000 cpm, or a 0.1-ml sample in a liquid scintillator gave a beta count rate of between 50,000 and 100,000 cpm. The addition of NH4OH was used to obtain pH values greater than 1. For 115mIn,the equilibrium 115Cd-115mInmixture was adjusted to a pH of 4, equilibrated with an equal volume of 0.1M TTA in MIBK, the phases separated, and the 11jmIn extracted from the organic phase into 0.1N HCl. The pH’s of the tracer solutions, which were less than 1, were computed from the normality of the diluting acid. For the preparation of 204Tl(I) solutions, HNOs was used instead of HCl. LIQUID SCINTILLATION “COCKTAIL.” The liquid scintillator was prepared by dissolving 7 grams of 2,5-diphenyloxazole (PPO), 0.375 gram of 1,4-bis-2(5-phenyloxazolyl)benzene (POPOP), and 150 grams of naphthalene in 1 liter of dioxane. Procedure. The procedure, except where noted, was to equilibrate a 5-ml aqueous solution containing a radioactive tracer with a 5-ml 0.1M TTA-MIBK solution in a 1-oz glass vial for 10 minutes at room temperature. The shaking speed was set at the maximum with the vials moving in an arc of about 7 inches in radius. After separation of phases the pH of the aqueous phase was measured. For gamma counting, 2-ml volumes of the aqueous and organic phases were pipetted into plastic vials. The energy window of the single channel analyzer was adjusted for the tracer of interest and the samples were counted under fixed geometry for a time period of up to 10 minutes in order to minimize statistical counting errors. For beta counting, a liquid scintillation procedure developed by Beihn and Noakes (7) for minimizing chemical (7) R. M. Beihn and J. E. Noakes, Oak Ridge Associated Univ.,
Oak Ridge, Tenn., personal communication, 1970.
ANALYTICAL CHEMISTRY, VOL. 42, NO. 11, SEPTEMBER 1970
Table I. Distribution of Beryllium between Aqueous Chloride Solutions and 0.1M TTA in MIBKa PH Dist. coeff. (D)
0
1.30 1.64 1.97 2.03 2.60 3.28 3.45 4.02 4.28 4.77 5.17 5.72 Distribution from aqueous to
3.03 f 0.23 X 3.69 f 0.06 X 1.03 f 0.01 X lo-' 1.22 4 0.01 x 10-1 1.45 4 0.01 x 10-l 4.03 f 0.03 X 10-l 6.81 4 0.04 X 10-l 2.52 f 0.02 X loo 8.53 f 0.08 X loo 1.08 f 0.03 X loz 5.26 -I: 0.50 X lo2 5.81 =!= 0.69 X IO2 organic phase only.
isotopes for 5 of the 18 Group I1 and Group 111 elements. Thus, distribution studies were not made for magnesium, radium, boron, aluminum, and actinium. According to Irving (8), the solvent extraction of a metallic inner complex, MR,, formed by the equation Mn+
quenching from sample solutions was used. A 0.1-ml sample from each phase was pipetted into glass counting vials and evaporated with gentle heating, almost to dryness. Then, 10 ml of the liquid scintillation cocktail was added to each vial. The beta energy window was selected to give a maximum count rate for the tracer and the count rates for the samples were measured. The relative quenching for each sample was measured by the internal standard ratio method. The attainment of equilibrium for each element was tested by recombining the phases including the 2-ml gamma counting samples, adding a drop or two of acid to lower the pH, then equilibrating, and remeasuring the p H and activity in each phase as described above. Except as noted for metal ions in which reversible equilibrium was not obtained, at least three measurements were made in this way for each element. The values for the distribution coefficient, D , of the metal ions, where
D = -[M"+] Organic Phase [M"+] Aqueous Phase were calculated from the ratio of the counting rates for the organic and aqueous phases. The standard deviation for each distribution coefficient was calculated from the respective count rate standard deviations. RESULTS AND DISCUSSION
The high degree of sensitivity and the specificity with which radiotracers can be detected make them ideally suitable for the determination of solvent extraction distribution coefficients. One limitation in their use is that suitable radioactive isotopes either do not exist or are not readily available for every element. The investigators were unable to secure suitable radio-
+ nHR e MR, + nHf
(1)
where nHR represents TTA in the enol form, is susceptible to a relatively simple and general treatment. First, TTA and the TTA chelate complex exist as simple, unassociated molecules in both phases. Second, solvation is not significant in the process of extraction. Finally, the solutes are uncharged molecules and their concentrations are usually so low that physical chemistry of an ideal solution is applicable. Thus, from Equation 1, a tenfold increase in TTA concentration has the same effect on the distribution coefficient as a one-unit decrease in pH. That is, increasing TTA concentration should result in a lateral shift of the distribution coefficient curves t o regions of higher acidity. Group IIa Elements. Beryllium is notable for its tendency to form complex organic compounds in contrast to the other alkaline earth elements. Thus, the apparent tendency to form a fairly stable complex with TTA was not surprising. The data shown in Table I were obtained by extraction into the 0.1M TTA-MIBK phase. The reverse equilibrium rate was found to be very slow. For example, a 10-minute equilibration of the organic phase shown in the Table for pH 5.17 with 0.2N HCl resulted in a distribution coefficient of 4.68. When log D for the data shown in Table I is plotted us. pH, a departure from the usual S shaped curve having a linear portion in the center is noted at a pH of about 2. This is interpreted as a change in the species being extracted into the organic phase. Recognizing the increased stability of TTA-MIBK solutions for alkaline extractions, Akaza (6) studied the extraction of magnesium, calcium, strontium, and barium into 0.2M m A in MIBK. Atomic absorption was used t o determine the metal ion content of each phase. When log D , for calcium, strontium, and barium, is plotted cs. pH from the data shown in Table I1 and compared with similiar plots of Akaza's data at a pH of 6, the present study shows a higher D value for barium. Also, the expected 0.3 p H unit shift of Akaza's curves toward regions of higher acidity, because of his use of 0.2M TTA, is not evident. The evaporation technique utilized in the preparation of the liquid scintillation samples for beta counting was new to (8) H. M. Irving, Quart. Rev. Chem. SOC.,5, 200 (1951)
Table 11. Distribution of Calcium, Strontium, and Barium between Aqueous Chloride Solutions and 0.1M TTA in MIBK
PH 2.90 4.07 4.67 4.95 5.28 5.45
5.87 6.06 6.46 6.85 7.16 7.68
Calcium Dist. coeff. ( D ) 2.18 =t0.14 X 2.87 4 0.18 X 1.19 f 0.03 X 5.49 f 0.08 X 4.29 & 0.03 X 10-l 8.40 f 0.04 X 4.52 f 0.03 X 1.88 4 0.02 X 9.46 =k 0.18 X
lo-'
100 10' 101 2.65 4 0.09 X lo2 3.25 f 0.15 X loz 5.14 f 0.39 X lo2
PH 3.38 4.20 4.92 5.37 5.86 5.97 6.23 6.40 6.92 7.52 8.25 8.57
Strontium Dist. coeff. (D) 3.34 40.21 x 10-3 4.77 f 0.23 x 10-3 9.04 f 0.26 x 2.20 f 0.04 X 1.78 f 0.02 x 10-1 2.47 f 0.02 x 10-1 8.37 f 0.08 x 10-1 1.87 f 0.02 X loo 1.68 f 0.02 x 10' 1.04 f 0.03 X lo2 2.16 f 0.10 X lo2 2.48 f 0.11 X lo2
PH 4.75 5.10 5.44 5.80
6.07 6.28 6.54 6.75 6.93 7.18 7.45 8.15
Barium Dist. coeff. (D) 1.68 =t0.12 X 6.14 f 0.16 X 10-3 1.75 =k 0.02 x 10-2 4.38 f 0.05 X 2.14 =k 0.02 X 10-l 5.27 f 0.04 X 10-1 1.65 f 0.01 X 100 4.60 f 0.04 X 100 1.04 f 0.01 X 101 3.92 f 0.08 X 101 1.22 4 0.02 x 102 4.65 f 0.21 X 102
ANALYTICAL CHEMISTRY, VOL. 42, NO. 11, SEPTEMBER 1970
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Table 111. Distribution of Zinc, Cadmium, and Mercury between Aqueous Chloride Solutions and 0.1M 'ITA in MIBK
PH 1.88 2.25 2.82 3.08 3.51 4.10 4.33 4.85 5.12 5.65 5.70 6.80
Zinc Dist. coeff. (D) 3.81 f 0.20 x 10-3 4.06 0.02 x 10-3 1.30 f 0.03 X 1.45 f 0.04 x 1.01 f 0.01 x lo-' 9.29 f 0.10 x 10-1 1.55 f 0.02 X lo6 1.59 f 0.02 X 10' 2.78 f 0.04 X 10' 1.53 f 0.05 X lo2 2.16 f 0.09 X loz 9.02 f 0.95 X lo2
PH 3.62 3.75 4.10 4.20 4.40 4.55 4.85 4.95 5.21 5.41 5.55
5.81 6.15 6.60 7.60
Cadmium Dist. coeff. (D) 1.36 f 1.77 x 10-8 3.87 f 1.73 X 10-3 1.05 f 0.19 x 10+ 1.76 f 0.30 X 10-2 5.85 f 0.39 X 10-2 1.01 f 0.04 x 10-l 3.20 f 0.08 x 10-1 5.14 f 0.12 x 10-1 1.53 f 0.03 X 100 4.13 f 0.09 X 100 7.75 f 0.23 X 100 2.68 f 0.17 X 101 1.06 f 0.20 X 102 4.46 f 0.30 X lo2 7.30 f 0.75 X lo2
PH 0.11 0.83 1.63 2.10 3.10 3.65 3.93 4.86 5.20 5.96 7.03
Mercury Dist. coeff. (D) 1.81 f 0.01 X 100 2.46 f 0.02 X 100 3.13 f 0.02 X 100 3.15 f 0.02 X loo 4.53 =!= 0.03 X loo 5.08 f 0.02 X 100 5.18 f 0.04 X loo 9.24 f 0.18 X 100 1.24 f 0.03 X 101 1.05 =!= 0.02 X 101 1.36 f 0 . 0 2 X 101
Table IV. Distribution of Scandium, Yttrium, and Lanthanum between Aqueous Chloride Solutions and 0.1M TTA in MIBK PH 0.0 0.3 0.42 0.69 0.70 1.25 1.50 1.75 2.10 2.40 2.57 3.12 3.60
Scandium Dist. coeff. (D) 1.71 f 0.30 X 4.53 f 0.35 x 1.67 f 0.04 x 3.10 f 0.05 x 6.39 f 0.10 X 7.18 f 0.04 X 10-1 4.19 f 0.03 X loo 2.56 f 0.04 X 10' 1.39 f 0.05 X lo2 3.17 f 0.18 X lo2 4.24 f 0.29 X IO2 5.86 =!= 0.53 X lo2 7.88 f 0.85 X lo2
PH 2.15 2.40 2.65 2.80 3.02 3.20 3.48 3.70 4.02 4.20 4.42
Yttrium Dist. coeff. (D) 6.40 i 0.20 x 10-3 1.85 f 0.04 x 10-2 6.30 f 0.07 X 1W2 2.14 f 0.02 X 10-1 1.15 f 0.01 X IO0 3.15 f 0.03 X 100 1.26 f 0.01 X 10' 5.90 f 0.11 X 101 2.23 f 0.09 X lo2 3.16 i 0.14 X 102 6.55 f 0.34 X loz
the investigators. Also, there was the question of chemical quenching of the count rates by TTA for the organic phase samples. Thus, for calcium, atomic absorption was chosen as a reference procedure. Using this method, values for D of 0.276, 1.76, and 7.22 were obtained for the pH's of 5.18, 5.38, and 5.80, respectively. When log D is plotted us. pH for these values and compared with the same plot of the data for calcium from Table 11, which was corrected for quenching, excellent agreement is noted. The quenching effect of the TTA-MIBK phase samples was only slightly greater than for the aqueous phase samples. By comparison the average value of the internal standard ratio was 0.661 for the TTA-MIBK phase samples and 0.802 for the aqueous phase samples. Since D is a ratio, the net effect of correcting the count rates for quenching was a very slight shift of the D values in the direction of lower pH. From a practical stand-point, the difference resulting from sample quenching is not significant. Group IIb Elements. The distribution coefficients for zinc, cadmium, and mercury as a function of p H are shown in Table 111. When the log D values are plotted us. pH, zinc and cadmium show the expected extraction into the organic phase by TTA with increasing pH. The point of equal distribution between the two phases occurs at about pH 4 for zinc and pH 5 for cadmium. However, the flat slope of the curve for mercury indicates that it behaves in a manner that is completely different. This suggests that the simple extraction of the metallic ion-TTA chelate does not occur for mercury. Group IIIa Elements. The extraction of yttrium into organic solutions of TTA was studied extensively by Schweit1244
PH 1.48 2.26 2.92 3.15 3.38 3.61 3.75 4.20 4.33 4.68 4.92
Lanthanum Dist. coeff. (D) 8.0 0.0 x 10-4 1 . 0 =!= 0.0 x 10-3 2.05 f 0.01 x 10-2 1.03 f 0.01 x 10-1 7.66 f 0.04 X 10-1 6.50 f 0.05 X 100 1.96 f 0.01 X 101 8.17 f 0.08 X 101 1.26 f 0.02 X lo2 7.92 f 0.33 X lo2 9.33 f 0.44 X 102
zer and McCarty (9) using 9lY as a radioactive tracer. A portion of their study was devoted to TTA-MIBK solutions as the organic phase, which included one series of equilibrations with 0.1M TTA in MIBK. The equilibrium coefficients for the elements scandium, yttrium, and lanthanum from the present study are shown in Table IV. When the yttrium data are plotted and compared with the plot of Schweitzer and McCarty's data, the points of equal distribution between the two phases for both studies are at pH's of 3.0 and 2.8, respectively. This close agreement was achieved even though Schweitzer and McCarty used perchlorate solutions, equilibrated the solutions for 9 hours, and maintained the temperature at 30 f 0.5 "C. Referring again to Equation 1, plots of Schweitzer and McCarty's data for TTA concentrations of 0.003M, O.O3M, and 0.3M show an exact shift downward of one pH unit in the midpoint of the curves for each tenfold increase in TTA concentration. Comparative plots of log D us. pH for the scandium, yttrium, and lanthanum data shown in Table I V results in similar almost parallel curves, whose points of equal distribution occur at pH's of 1.2, 3.0, and 3.4, respectively. The slope of the straight midsection of each curve is steeper than for the Group I1 elements, as expected from the higher ionic charge. Group IIIb Elements. The results from these studies showed broad differences in extraction behavior for the three elements, gallium, indium, and thallium. Gallium is classified here as a special case, because equilibrium between the (9) G. K. Schweitzer and S. W. McCarty, Aizal. Chim. Acta., 29, 56 (1963).
ANALYTICAL CHEMISTRY, VOL. 42, NO. 11, SEPTEMBER 1970
Table V. Distribution of Gallium between Aqueous Chloride Solutions and 0.1M TTA in MIBKa Distribution coefficient (D)
Q
PH Equilibration (10 min) 0.74 4.38 f 0.33 X 1.05 5.35 0.34 x 10-3 1.42 9.35 0.38 x 10-3 1.92 5.53 f 0.07 X 2.10 9.98 f 0.09 x 2.21 2.29 f 0.01 X lo-' 2.83 f 0.02 X lo-' 2.35 5.80 f 0.04 X lo-' 2.55 2.78 1.24 f 0.01 X loo 5.84 f 0.07 X loo 2.90 8.03 f 0.07 X loo 2.99 4.36 f 0.48 X lo2 3.75 5.13 f 0.89 X lo2 4.84 Distribution from aqueous to organic phase only.
Equilibration (30 min) 5.25 f 0.34 x 8.36 f 0.38 X 2.24 f 0.05 X 1.35 f 0.01 x 10-l 2.55 f 0.02 X lo-' 5.26 f 0.03 X 10-1 4.41 f 0.02 X lo-' 1.44 f 0.01 x 100 7.31 f 0.06 X IOo 8.93 f 0.60 X 10' 1.36 f 0.07 X 10% 6.48 f 1.03 X lo2 7.02 f 1.61 X l o 2
Equilibration (60 min) 6.71 f 0.36 x 10-3 1.02 f 0.04 X 10-2 3.95 f 0.06 X 2.53 f 0.02 x 10-1 4.75 f 0.03 X 10-1 1.01 f 0.01 x 100 6.89 f 0.03 X 10-1 2.95 f 0.02 X 100 8.26 f 0.27 X 101 2.00 f 0.27 X 102 2.99 rfi 0.28 X 102 7.05 f 1.20 X 102 8.15 f 2.16 X 102
Table VI. Distribution of Indium and Thallium between Aqueous Solutions and 0.1M TTA in MIBK
a
Indium PH Dist. coeff. (D) b. 31 2.68 f 0.81 X (114m) 1.50 3.71 f 0.32 X 1.65 1.22 f 0.11 x 10-2 (114m) 2.03 3.12 f 0.08 X 2.15 5.34 f 0.13 X lo-' (114m) 2.95 1.23 f 0.01 X loo 3.00 2.40 f 0.04 X loo 3.15 4.18 f 0.06 X loo (114m) 3.38 1.61 f 0.03 X 10' 3.48 2.33 f 0.04 X 10' (114m) 3.89 5.95 f 0.21 x 10' 1.33 f 0.05 X lo2 4.45 3.63 f 0.45 X lo2 5.07 9.51 f 3.30 X lo2 5.52 1.22 f 0.56 X lo3 6.20 Nitrate solutions used for aqueous phase.
Thalliums
PH 3.80 4.33 4.70 4.94 5.58 6.12 6.43 7.05 7.73 8.62 9.15
Dist. coeff. (D) 6.40 0.21 x 10-3 1.24 f 0.03 X 10-2 2.24 f 0.04 X 10-2 3.79 f 0.05 X 10-2 1.20 f 0.01 x 10-1 3.36 f 0.02 X 10-1 6.38 f 0.03 X 10-1 3.24 f 0.02 X 100 1.30 f 0.01 X 101 3.03 f 0.01 X 101 3.28 & 0.04 X 101
*
Table VII. Group I1 and Group I11 Element Pairs with Single Stage Separation Factors of 1000 or Greater Element pair pH Range Aqueous phase Organic phase Scandium 2.0-2.2 Yttrium Scandium 2.0-2.3 Indium Scandium 2.0-2.8 Zinc Scandium 2.0-2.8 Lanthanum Scandium 2.0-4.0 Cadmium Scandium 2.0-4.3 Thalium Scandium 2.0-4.6 Calcium Scandium 2.0-4.8 Strontium Scandium 2.0-5.3 Barium Yttrium 3.8-4.0 Cadmium Yttrium 3.8-4.3 Thallium 4 Parent-daughter radioisotope pair.
aqueous and organic phases was not achieved in the standard 10-minute equilibration time. Also, extraction from the organic to the aqueous phase takes place at a much slower rate than from the aqueous to organic phase. The distribution coefficient data shown in Table V were obtained by extraction of gallium from the aqueous phase. A plot of log D U S . pH indicated that the difference in D values for the 10minute and the 60-minute equilibrations are minimized if the pH of the aqueous phase is either less than 1 or greater than 4. A limited number of equilibrations were made t o determine the optimum conditions for extraction of gallium from the organic to the aqueous phase. The most effective HC1 concentration for a 10-minute equilibration was found t o be 0.2N. Also, a series of equilibrations were carried out to test the hypothesis that heat should accelerate the breakup of the gallium-TTA chelate. Four samples of O.1MTTA in MIBK
pH Range 3.84.6 3.84.8 3.8-5.3 3.84.2 3.84.3 4.0-4.2 4.2-4.3 4.2-4.6 4.2-4.8 4.2-5.3
Element pair Aqueous phase Organic phase Calcium Yttrium Strontium" Yttrium0 Barium Yttrium Cadmium0 Indiuma Thallium Indium Cadmium Lanthanum Thallium Lanthanum Calcium Lanthanum Strontium Lanthanum Bariuma Lanthanum"
containing gallium were equilibrated with 0.2N HC1 for 10 minutes. For the solution temperatures at the start of 25, 60, 80, and 90 "C, the values of D were 5.94 x 10-2,2.20 x 1.54 X and 1.20 X respectively. Although, the temperatures of all samples at the end of the equilibrations were at room temperature, the trend indicates that heat should be effective in accelerating the extraction into the aqueous phase. The distribution coefficient data for indium and thallium(1) are shown in Table VI. The results for indium are particularly interesting because the initial D values were obtained using llSmIn, which had been separated from the parent 115Cd at a p H of 4. The later availability of 114mIn gave the investigators the opportunity t o check the data using this radiotracer. For comparison, five measurements labeled (114m) are included in Table VI. A plot of log D us. p H
ANALYTICAL CHEMISTRY, VOL. 42, NO. 11, SEPTEMBER 1970
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shows the excellent agreement between use of the two indium tracers. A change in slope at about p H 3.4 is attributed t o a probable change in the indium species being extracted. The thallium system was different from the other two members of this subgroup in two respects: First, the initial aqueous solution prior t o adjustment of p H was 0.1N ”01; and second, the normal valence state for thallium in dilute aqueous solutions is 1. The shift in D values t o the higher p H region was attributed t o the 1 valence state for the thallium ion. Also, the much flatter slope than for other Group I1 and Group I11 elements, according t o Irving and Williams ( l o ) ,indicates a lower valence for the metal ion being extracted.
+
+
(10) H. M. Irving and J. Williams, J . Chem. Soc., London, 1841 (1949).
CONCLUSIONS The foregoing study shows that an aqueous us. TTA-MIBK extraction system can be used for the separation of many Group I1 and Group I11 elements. The element pairs with single stage separation factors of 1000 or greater are shown in Table VII. Further, the use of MIBK as a solvent for TTA results in a system that is stable for basic, as well as for very acid, aqueous solutions, and which is remarkably free of the problems of emulsification and slowness of phase separation.
RECEIVED for review March 18,1970. Accepted June 24,1970. Presented at the 21st Southeastern Regional Meeting, ACS, Richmond, Va., Nov. 5-8, 1969. Work supported ,by the U. S. Atomic Energy Commission under contract with Oak Ridge Associated Universities,
X-Ray Excited Optical Fluorescence Spectrometry. Scope of Application to Trace Rare Earth Determinations Edward L. DeKalb, Arthur P. D’Silva, and Velmer A. Fassel Inrtitute f o r Atomic Research and Department of Chemistry, Iowa State University, Arne.r, Iowa 50010 X-Ray excited optical fluorescence spectrometry is shown to be capable of detecting the presence of rare earth impurities at concentrations of 100 ppm or less in compounds prepared from 49 of the chemical elements. Several of the more complex compounds provided detectabilities superior to the simple oxides. The excitation mechanism for production of these spectra i s also reviewed.
THESHARP-LINE optical fluorescence emitted by trace rare earth constituents of a sample irradiated by X-rays has been employed by a number of authors (1-7) for the quantitative determination of fractional part per million amounts of most of the rare earth elements in Y203,Gdz03,Thoz, and several ionic fluoride matrices. In view of the excellent reported detectabilities, we have undertaken an exploration in depth on the scope of application of this technique t o the practical determination of trace rare earth impurities in other matrices. The data reported in this communication show that compounds prepared from 49 elements support analytically useful X-ray excited optical fluorescence of one or more rare earth impurity. BASIC PRINCIPLES Many inorganic and organic compounds luminesce when they are irradiated by X-rays (8, 9). Several authors have (1) R. C. Linares, J. B. Schroeder, and L. A. Hurlburt, Spectrochim. Acta, 21, 1915 (1965). (2) J . F. Cosgrove, D. W. Oblas, R. M. Walters, and D. J. Bracco, Electrochem. Technol., 6 , 137 (1968). (3) W. E. Burke and D. L. Wood in “Advances in X-ray Analysis,” Vol. 11, J. B. Newkirk, G. R. Mallett, and H. G. Pfeiffer, Ed., Plenum Press, New York, 1968, pp 204-213. (4) N. Sasaki, Biinseki Kagaku, 17, 1387 (1968). (5) W. A. Shand, J . Mater. Sci., 3, 344 (1968). (6) R. J. Jaworowski, J. F. Cosgrove, D. J. Bracco, and R. M. Walters, Spectrochim. Acta, 23B,751 (1968). (7) T. R. Saranathan, V. A. Fassel, and E. L. DeKalb, ANAL. CHEM., 42, 325 (1970). (8) H. W. Leverenz, “An Introduction to Luminescence of Solids,” Wiley, New York, 1950, pp 421-427. (9) D. Curie, “Luminescence in Crystals,” Wiley, New York, 1960, pp 298-301. 1246
suggested mechanisms for the excitation and emission processes (10-22). Although all aspects of the phenomenon d o not appear t o be clearly understood, it is possible to draw useful generalizations from the experimental data and the suggested mechanisms. The absorption of an X-ray photon by a n atom results in the ejection of a photoelectron from one of the inner electron shells of that atom. If the atom is in the solid state, the ejected photoelectron may yield its free energy in random-sized “bits” of 10 to 30 eV to other atoms of the matrix, which causes them to become either excited or ionized. A single absorbed X-ray photon may thus produce many such secondary excitants (23). These secondary exci(10) H. W. Leverenz, “An Introduction to Luminescence of Solids,” Wiley, New York, 1950. (11) P. R. Thornton, “Scanning Electron Microscopy,” Chapman and Hall, London, 1968, Chapter 10. (12) L. G. Van Uitert in “Luminescence of Inorganic Solids,” P. Goldberg, Ed., Academic Press, 1966, Chapter 9. (13) L. G. Van Uitert, J . Electrochem. Soc., 114, 1048 (1967). (14)F. Matossi and S. Nudelman in “Methods of Experimental Physics,” Vol. 6, Part B, K. Lark-Horovitz and V. A. Johnson, Ed., Academic Press, New York, 1959, pp 293-294. (15) G. Blasse and A. Bril, J. Electrochem. SOC.,115, 1067 (1968). (16) G. Blasse, J . Chem. Phys., 45, 2356 (1966). (17) J. Makovsky, W. Low, and S. Yatsiv, Phys. Lett., 2, 186 (1962). (18) W. Low, J. Makovsky, and S. Yatsiv in “Quantum Electronics-Paris 1963 Conference,” Columbia University Press, New York, 1964, p 655. (19) L. G. Christophorou and J. G. Carter, Nature, 209, 678 (1966). (20) H. N. Hersh and H. Forest, in “Proceedings of the International Conference on Luminescence,” F. Williams, Ed., North Holland Publishing Co., Amsterdam, 1970, pp 862-868; J . Luminescence, 1, 2, 862 (1970). (21) E. R. Ilmas and T. I. Savikhina, in “Proceedings of the International Conference on Luminescence,” F. Williams, Ed., North-Holland Publishing Co., Amsterdam, 1970, pp 702-715; J. Luminescence, 1,2,702 (1970). (22) 1. A. Parfianovich, E. I. Shuraleva, and P. S . Ivakhnenko, Bull. Acad. Sci. USSR,Phys. Ser., 31,838 (1967). (23) H. W. Leverenz, “An Introduction to Luminescence of Solids,” Wiley, New York, 1950, pp 316-318.
ANALYTICAL CHEMISTRY, VOL. 42, NO. 11, SEPTEMBER 1970
