Separation of Strontium-90 and Yttrium-90 by Isotopic Exchange Thin Layer Ch romatography Rokuro Kuroda and IKoichi Oguma' Laboratory for Analytical Chemistry, Faculty of Engineering, University of Chiba, Yayoi-cho, Chiba, Japan
MANYSPECIFIC METHODS have been developed for separating radioisotopes by isoto,pic exchange reactions. Meinke and collaborators (1-6) have worked out the effective separation of various radionuclides by amalgam exchange techniques. An interesting application of isotopic exchange to the determination of mercury in a solvent extraction system has been reported by Handley (7). Qureshi has effected the separation of radioactive cobalt (8) and antimony (9) by isotopic exchange using a respective insoluble compound. An isotopic-ion exchange method has recently been developed
(1) J. R. DeVoe, C. K. Kim, and W. W. Meinke, Tulantu, 3, 298 (1960). (2) J. R. DeVoe, H. W. Nass, and W. W. Meinke, ANAL.CHEM., 33, 1713(1961). (3) W. B. Silker, Zbid., 33,,233 (1961). (4) R. R. Ruch, J. R. DeVoe, and W. W. Meinke, Tuluntu, 9, 33 (1962). (5) I. H. Qureshi and W. W. Meinke, Zbid., 10,737 (1963). (6) F. E. Orbe, I. H. Qureshi, and W. W. Meinke, ANAL.CHEM., 35, 1436 (1963). (7) T. H. Handley, Zbid., 36, 153 (1964). (8) I. H. Qureshi, Tulanru, 11, 1550 (1964). (9) I. H. Qureshi and M. Shabbir, Zbid., 13, 847 (1966).
by Tera and Morrison (IO) for the rapid multitrace-element separation from large amounts of radioactive matrix elements. Isotopic exchange in gas chromatography has also been applied to the labeling of inorganic compounds, determination of inorganic compounds separated by gas chromatography, and a study of the interaction between the solid stationary phase and the solute in gas-liquid chromatography (11, 12). Until now no application of the isotopic exchange reaction to thin layer chromatography has been reported. In this work the isotopic exchange reaction has been utilized in thin layer chromatography so that the separation of carrier-free Y-90 and its parent Sr-90 can be achieved in a rapid and simple way. By using an equilibrium mixture of Sr-90 and Y-90 on a SrS04 layer and developing with dilute HzS04, Sr-90 is retained, while Y-90 advances upward almost to the HzSOafront, so that a clear separation can be accomplished rapidly. 1 Present address, Government Chemical Industrial Research Institute, Shibuya-ku, Tokyo, Japan.
(10) F. Tera and G . H. Morrison, ANAL.CHEM., 38, 959 (1966). (11) J. Tadmor, Zbid., 36, 1565 (1964). (12) J. Tadmor, Zbid., 38, 1624 (1966).
x 10
SA
90
Sr
9 0r ~
1
s*f:
9oY
D I. S T A N CE (cm)
1
)O
s,f.
Sr
I
d
Figure 1. Thin layer chromatographic separation of Sr-90and Y-90 Developing agent: (a) 1N H B 0 4 . (b) 0.1N HSOr (c) 0.01N HS04 s.f. = solvent front VOL. 39, NO. 8, JULY 1967
0
1003
s:f.
s,f.
1
D
I.
C
B
1
wY
90
Sr
R 4
0
8
-3
Figure 2. Effect of silica gel in adsorbent mixtures on the chromatographic behavior of Sr-90 and Y-90 Adsorbent: ( D ) 25 Z SrS04
+ 75 Z silica gel
(050 Z SrS04
EXPERIMENTAL
A commercially available crystal powder of %SO4 was treated with boiling HNOI (1 :1) for 1 hour. SrS04 crystals thus activated were washed with distilled water, followed by 95% ethyl alcohol. The crystals were then dried in an air oven at 80" C for 1 hour and cooled in air. A slurry of the sulfate, prepared by mixing the sulfate with soluble starch, varying amounts of silica gel, and distilled water, was spread 250 microns thick on 2.5 X 20 cm2 glass plates with an applicator assembly. The plates were air-dried and then heated in an oven at 80 O C for 45 minutes. Adsorbent systems utilized were: (A) 100% SrS04 no silica gel; (B) 75% SrS04 25% silica gel; (C) 50% SrS04 50 % silica gel; and (D) 25 % SrS04 75 % silica gel. To each adsorbent system 5 % soluble starch was added to ensure a stable thin layer. Approximately 5 p1 of 0.01N HC1 solution containing the equilibrium mixture of Sr-90 and Y-90 were applied to the plate (25 mm away from the edge) with a glass capillary, and air-dried for 20 minutes. The spot was then developed by the ascending technique with 0.1N HzS04 solution except for system A, in which the concentration of H2SO4 was varied from 0.01 to lN, until the solvent front had traveled 12 cm high. Subsequently, the plate was air-dried and Sr-90 and Y-90 were detected on the plate with a conventional Geiger-Muller counting scanner. Two sections, 1 cm wide, of the layer of system A (obtained by development with 0.1N HzS04),which correspond to peaks of Sr-90 and Y-90, respectively, were scraped off the plate, placed in counting trays, and subjected to decay and growth rate measurements.
+
+
+
+
RESULTS AND DISCUSSION
Thin layer chromatographic behavior of Sr-90 and Y-90 in adsorbent system A coupled with HzS04 of varying concentrations as a developing agent is illustrated in Figure 1. 1004
0
ANALYTICAL CHEMISTRY
+ 50% silica gel
( B ) 75 Z SrSO4
+ 25 % silica gel
Sr-90 is retained by the isotopic exchange, while Y-90 moves upward rapidly along with the solvent front, showing a R, value of about 0.90, When the concentration of &So4 decreases to O.OlN, however, a part of the Sr-90 tends to advance and Y-90 tails markedly over almost the entire range through which the major portion of Y-90 passes. This may be due to the hydrolysis of Y-90 at lower concentration of HzS04. With the increasing concentration of H2S04, the spread of both spots of Sr-90 and Y-90 becomes less marked, thus providing good separation. The effect of silica gel in adsorbent mixtures on the behavior of Sr-90 and Y-90 is illustrated in Figure 2, where 0.1N was used as the developing agent throughout. With increasing proportions of silica gel the spot of Sr-90 broadens out, while that of Y-90 tends to become more sharp. R1 values of Y-90 increase also with increasing proportions of silica gel: 0.89 for the system B, 0.94 for C, and 0.99 for D, respectively. The time required for the solvent front to travel 12 cm high, which is sufficient for good separation, is only 16 minutes for system D, -30 minutes for C, -40 minutes for B, and 45 minutes for A. Decay rate measurement of the Y-90 fraction showed no sign of contamination due to Sr-90 and the recovery curve for Sr-90 in the Sr-90 fraction was found to fit the theoretical formula. Use of HNOa (0.01 to 1N) was also attempted as a possible developing agent for the four adsorbent systems, but the separation was unsuccessful because of a rather high solubility of SrS04 in HNOa solutions. RECEIVED for review January 27, 1967. Accepted March 13, 1967.
