chlorides was investigated and the results are shown on Figure 3. Twenty micrograms of each metal as the chloride were heated in platinum crucibles a t various temperatures for 1 hour. All the salts volatilized at temperatures above 750’ C. Loss of rubidium and cesium started abruptly a t 500’ C. and was almost complete at 700’ C. Serious lithium, sodium, and potassium losses were observed above 600’ C. Calcium and magnesium were not volatilized to the extent of the alkalis. Figure 4 shows the retention of alkali fluorides after heat treatment. Table I11 lists the decreasing order of volatility a t 550’ C. for the alkali chlorides and fluorides taken from Figures 3 and 4. The compounds are also listed in decreasing order of vapor
pressure and increasing order of melting point. The vapor pressures a t 550’ C. were extrapolated from data of Stull(9). With the exception of lithium chloride and fluoride, the alkali salts fall into three identical orders of decreasing formula weight. From the data in Table 111, it can be seen that the relative volatility of the alkali chlorides a t 550” C. can be predicted on the basis of melting point and vapor pressure. LITERATURE CITED
( 1 ) Assoc. Offic. Agr. Chemists, “Methods of Analysis,” 6th ed., p. 559, Washington, D. C., 1945. (2) ASTM Standards, Methods of Testing, D811-48, D1026-51, and D1318-64. (3) Gorsuch, T. T., Analyst 84, 135 (1959).
(7) Ritter, R., -Vuturwissenschujten 51, 144 (1964). (8) Roscoe, H. E., Schorlemmer, C., “Treatise on Chemistry,” Vol. 11, p. 121, Macmillan, London, 1913. (9) Stull, S. R., Ind. Eng. Chem. 39 517 (1947). (10) Thiers, R. E., “blethods of Biochemical Analysis,” Vol. 5, Chap. 6,
D. Glick, ed., lnterscience, Sew York, 1957.
T. Y. KOMETANI Bell Telephone Laboratories, Inc. Murray Hill, N. J. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., hlarch 1966.
Ra pid Rad ioche mica I Se pa rations of S tro nti um-90-Y tt rium-90 and Calcium-45-Scandium-46 on a Cation Exchange Resin SIR: Y90 is extensively used in medicine, both in research and as a means of providing intense local radiation to various parts of the internal body. Moreover, Y90 is often required in the purest form as a standard beta source for calibration in nuclear spectrometry. Numerous methods for its separation from Sr90 have been reported (5-6,11). Radioactive calcium of high specific activity is required as a tracer, like Y”, in many investigations, particularly biological ones. Neutron irradiation of natural calcium gives preparations of Ca45with low specific activity, because of low neutron capture cross section and low percentage (-2.1%) of Ca44in the natural mixture, Preparations of high specific activity could be obtained by irradiating an enriched sample of Ca4‘, but this method is costly. Ca45is more suitably produced by (n,p ) reaction on natural scandium. The production of Ca45 in a carrier-free form from scandium and its separation from other alkaline earths by various methods have been reported (6,Y). Recently, Macasek and Cech (8) have described a procedure for the separation of Y90 from Sr” using EDTA and Dowex 50-X2 resin. Strelow (IO), on the other hand, has published a paper in which is given equilibrium distribution coefficients of more than 40 elements between Dowex 5OW-XS resin and different normalities of nitric and sulfuric acids. Before this, dilute nitric acid was employed for the separation of Razz* from Ac22* and other decay products of RaZz4( I ) and also for the purification of Ba140 from Lala (8). 1598 *
ANALYTICAL CHEMISTRY
This work is the continuation of that described earlier ( I , 9). Most of these procedures were developed either for preparing Y90 tracer from Sr” or for purifying Ca45. This paper describes a simple and rapid procedure for separating SrgOfrom Yw and producing Ca45 from scandium target employing a cation exchange resin and dilute nitric acid. This acid could be removed easily and quickly to obtain clean and carrier-free sources of Srw and Ca45. Briefly, fast milking of Y” from Srw employing easily available lactate solution is described. EXPERIMENTAL
Reagents. Baker analyzed Dowex 50W-X8 resin (200-400 mesh) was used. lMost of this resin, when graded in a water column, settled within 20 minutes a t a height of 30 cm. This fraction was selected for the study. Merck guaranteed reagent nitric acid and lactic acid were employed. Dilute solutions from 0.5 to 2.5 moles per liter were prepared from the former after making it colorless. Ammonia was used to prepare solutions of the latter at various pH values. Phenol, the final concentration of which was O.ZOJ,, was added as a preservative for lactate solutions. Tracer solutjons, Srw-Yw, So4, Ca4s and SrW9, were supplied by the Atomic Energy Establishment Trombay (A.E.E.T.), Bombay. These were diluted as desired. Their assaying was done by counting the activity with either a NaI(T1) scintillation spectrometer or with an end-window GeigerMuller tube employing a utility scaler (Type DS 411) supplied by A.E.E.T., Bombay.
Distribution Studies. Employing mg. of accurately weighed air-dried Dowex 50W-X8 resin con taining 32% moisture and tracers such as Sr55!Sg Y”, etc., in a known volume of either dilute nitric acid or lactate solution, the distribution studies were carried out a t 30’ & 1’ C as described (9). The shaking of the resin with the tracer solution was continued for about 5 hours, and the liquid counted thereafter. They were filtered through borosilicate-glass filters to remove suspended resin particles before counting. A11 these experiments were conducted in duplicate but in some cases where the duplicates did not agree, they were repeated to ensure accurate results. From the volume of the solution, the amount of the resin taken, and the counting rate of the solution before and after shaking, the equilibrium distribution coefficient was calculated in each case. The results so obtained were plotted on log X log and semilog paper and are shown in Figures 1 and 2. Separation of Srw from Yw and Cad5 from Sc&. An aliquot of Sr” in equilibrium with Y90 was evaporated to dryness in a beaker and a few drops of dilute nitric acid of a known concentration were added to it. The solution containing most of the activity was then transferred to a resin column of diameter 0.58 cm. and length 3.3 cm. (bed volume -0.87 ml.). The resin column was previously equilibrated with the same acid that was used to dissolve the tracers. The adsorbed activities were then eluted with dilute nitric acid of a known concentration a t a flow rate of about 1 cm. per minute. Two-milliliter portions were collected in test tubes. They mere monitored immediately. The elution was con50-100
A 0
x
tinued until the collection of one activity as seen from the elution peak was completed. Nitric acid was then changed to 3 moles/liter to expedite the elution of the remaining activity on the resin column. Employing a 4n plastic scintillator mounted on a photomultiplier and a nuclear data multichannel analyzer with 512 channels, a beta ray spectrum was taken for the activities collected. The sources, for this purpose, were prepared on thin Mylar films. The end point energy of 550 k.e.v. for the first fraction indicated that it was Srm. This beta ray spectrum of SrW showed no more YW present than that corresponding to the natural growth in the time interval between the separation and the measurement. The second fraction, suspected to be Ym, was counted daily for its decay for about 600 hours and a straight line plot giving 'v 64 hours confirmed that it was pure Yga. The entire procedure was repeated for various concentrations of nitric acid using a fresh mixture of the tracers SrW-YgO. Two representative curves are given in Figure 3. A similar experiment was carried out for a mixture of Ca45and Sc46 activities and representative data are given in Figure 3. Milking of YgOfromSrgO and Separation of Scu from Ca45. d n aliquot of Sr90 activity in equilibrium with YgO was adsorbed on a resin column similar to that described in the foregoing, but in the ammonium form and equilibrated previously with a lactate solution. Elution of Y90 was then carried out
Strontium, Slope = - 2 Yttrium, slope = - 3 Calcium, Slope = - 2 Scandium, slope = - 3
c
c
-I
L " " " " : " ~ " ~
4
10
-
w
-
a
-
I-
(z
a
5
10':
c
-
z 3
-
-
0
-
v
-
IOZ
:
A 30
VOLUME
40
IO
20
30
ELUATE, ml.-
from Dowex 50W-X8 resin by dilute Figure 3. Elution of Srgo-Ygoand Ca45-S~46 nitric acid VOL 38, NO. 1 1 , OCTOBER 1966
1599
Table 1. Comparison of Volume Distribution Coefficients Obtained from Peak Elution Volumes with Those Calculated from Distribution Coefficients, D, for Various Molarities of Nitric Acid
Scandium Nitric D V Obtained acid molarity from peak vol.
Calcium Nitric D, acid Obtained molarity from peak vol. 1.0 1.3 1.5 1.7 1.9
19.54 13.80 9.77 8.05 6.90
Yttrium Calcd. from D
Nitric acid molarity
D, Obtained from peak vol.
Calcd.
from D
Strontium
D,
Calcd. from D
Nitric acid molarity
Obtained from peak vol.
Calcd. from D
18.97 13.42 11.77 8.93 7.36
1.2 1.4 1.67 1.9 2.1
14.95 11.50 9.20 6.90 5.75
14.15 10.36 8.93 6.25 4.84
tion, 3M, wm found suitable to remove them quickly from the resin bed. 2.1M nitric acid was the optimum concentration of the acid to separate Sr9O and Yw rn well as Ca46and Sc46. During the milking of Y" from SrW by a lactate solution, it was observed that lowering the pH from 3.05 to 2.9 increased the collection volume to 120 ml. Hence, this curve was not given in Figure 4. Similar observation was made in the case of Sc46when the pH of the lactate solution was lowered from 2.7 to 2.6 (vide Figure 4). The peak volumes obtained from the elut'ion curves, when nitric acid was employed, were used to calculate volume distribution coefficients, D,, from the following relation
Dv
Peak vol., ml. = Resin bed vol., ml. =
with a lactate solution of a known pH until all the Yw came out, leaving Srw adsorbed on the column. The radiochemical purity of Yw was checked by following its decay. The procedure was repeated employing the same resin bed but with lactate solutions of various pH values between 2.9 and 3.45. The data so obtained are recorded in Figure 4. A curve for pH 2.9 is not given in the figure (vide Discussion). Similar experiments were carried out for a mixture of Ca45and Sca activities. The eluted fractions from an identical resin column were collected in 2-ml. portions and counted. After the removal of Sc" from the column with lactate solution, Cad6 activity adhering to the resin was removed from it with 2M ammonium nitrate solution. This procedure was then repeated with a fresh mixture of Ca4LSc" tracers employing a lactate solution of a different pH. The data so obtained for elution of Sc" with semimolar lactate solutions at various values of pH are given in Figure 4.
eluent. The continuation of the same acid (1.3-2 moles/liter) to elute either Yw or Sc46 was time-consuming. Hence, in these cases, slightly higher concentra-
D.p
where p is the bed density of the resin, which in the present case was found, independently, to be 0.566. Similarly,
DISCUSSION
Because of certain technical difficulties in the reactor, it was not possible to produce Ca45by (n,p ) reaction on scandium. Hence, a synthetic mixture of these tracers obtained from A.E.E.T., Bombay, was prepared and used in this work. Six different concentrations of nitric acid ranging from 0.9 mole per liter to 2.1 moles per liter were employed for the separations of Srw from YW and Ca45from Sc47 but only two representative curves in each case are given in Figure 3. The use of nitric acid of lower concentration than 1M collected the activity of Srw or Ca45 in a large volume of the solution. The acid concentration between 1.3 and 2M on the other hand wm adequate to remove all Srw or Ca45 in a small volume of the
1600
ANALYTICAL CHEMISTRY
-I
VOLUME
E L U A T E , ml,-
Figure 4.(A) Milking of Yw from Srw employing semimolar lactate solution at various pH values
x 0 1
3.45 3.10 3.2
7
A
3.35 3.05
(e)
Separation of S c 4 6 from Cad6 using semimolar lactate solution at various pH values A 2.8 2.9 0 2.7
x
2.6
the equilibrium distribution coefficient (D)values from Figure 1 were converted to D,values for every concentration of nitric acid studied and are given in Table 1. It is clear from Table I that D. values obtained from the peak volumes of the eluted activities and those calculated from distribution coefficients are in good agreement. ACKNOWLEDGMENT
The authors are grateful to Frederick Nelson of Oak Ridge National Laboratory for his comments on this paper.
G. W.,. Higgins, I. R., Roberts, J. T., in ‘‘Ion Exchange Technology,” F. C. Nachod, J. Schubert, e&., p. 419, Academic Press, New York, 1956. (10) Strelow, F. W. E., ANAL. CHEM. (9) Parker,
LITERATURE CITED
(1) Bhatki, K. S., Adloff, J. P., Radwchim. Acta 3, 123 (1964). (2) Bhatki, K. S., Ephraim, D. C., Inddian J . Chem. 4 (6), 261 (1966). (3) Doering, R. F., Tucker, X. D., Stang, J., J. Inorg. Nucl. Chem. 15, 215 (1960). (4) Goldin, A. S., Velten, R. J., Frishkorn, G. W., ANAL.CHEM.31, 1490 (1959). (5) Hamaguchi, H., Ikeda, N., Iwasa, A., Radioisotopes 13, 377 (1964). (6) Lerner, M., Rieman, W., ANAL. CHEM.26, 610 (1954). (7) Levin, V. I., Meshcherova, I. V., Marygina, A. B., Sarvetnikov, 0. E., Radwkhimiya 5 ( l ) , 37 (1963). (8) Macasek, F., Cech, R., Chem. Zvesti 19, 107 (1965).
37, 106 (1965). (11) Susuki, Y., Intern. J . A p p l . Radiutam Isotopes 15, 599 (1964).
A. T. RANE K. S. BBATKI~ Tata Institute of Fundamental Research Colaba, Bombay 5 BR India. 1 Correspondence regarding this publication may be addressed to this author.
Determination of Adsorbed Cobalt and Iron Ethyle ned initrilotetraacetate Com plexes on Platin urn Electrodes by Thin Layer Electrochemistry SIR: Previous studies in these laboratories in which diffusion chronopotentiometry was employed as the measuring technique ( 1 , 2) produced evidence that both cobalt(II1)-EDTA and cobalt(I1)-EDTA anions are extensively adsorbed on bright platinum electrodes. Quantitative measurement of the amount of each complex adsorbed was not attempted because of the poor definition of the waves and the possibility that the data contained some contribution from oxide film formation or supporting electrolyte reduction. When bromide or iodide ion was added to the solutions, the adsorption of the cobalt complexes appeared to be prevented, presumably because of the preferential adsorption of the halides. The general utility of the thin layer electrochemical technique for the quantitative study of adsorption has been established recently (7, 8) and we have applied i t to the cobalt-EDTA system to check the earlier results and to provide a quantitative measure of the extent of the adsorption. The ironEDTA complexes were also examined for possible adsorption. EXPERIMENTAL
The thin layer electrode was the micrometer type previously described ( 5 ) . The area of each face was 0.3175 sq. cm. The electrode was cleaned by alternate potentiostatic oxidation (1.2 volts us. SCE) and reduction (0.0 volts us. SCE) while a stream of oxygen was flowing across the free 1F electrode faces. After the cleaning cycle the electrode was maintained a t 0.4 volt us. SCE for several minutes until any residual current decayed to less than 1 Ha. Both linear potential sweep (8) and integral chronoamperometric [potential
step with current integration (S)] techniques were employed in the manner previously described. All solutions were deaerated with and stored under prepurified nitrogen. The electrode was enclosed in a polyethylene tent which was constantly swept with nitrogen that had been equilibrated with water at the laboratory temperature. Reagents. A 0.1F solution of cobalt(1IbEDTA ICOY-~) was nrepared ‘by mixing equimolar quantities of COS04~7HzOand Na2H2Y .2J+O in a I F pH 7 phosphate buffer solution. CrvstallineNa CoY.4H90 (11) was prepired as follows: An aqueous solution of B ~ ( C O Y ) ~ . ~ Hprepared ZO, according to the published procedure (9), was treated with a slight excess of NazS04, the resulting BaS04 removed by filtration, and the filtrate added to a large volume of anhydrous ethanol. The resulting precipitate was recrystallized from a n aqueous solution to give large violet crystals which were dried for 24 hours a t 50’ C. Purity of the crystals was confirmed by thin layer electrochemical analysis of weighed portions. Attempts to prepare pure NH4FeY HzO by the published procedure (8) were unsuccessful. However, NaFeY. 3H20 (4) was successfully obtained by the following modified procedure: A fresh precipitate of Fe(OH), was prepared by adding excess aqueous ammonia to a neutral solution of FeS04 in the presence of atmospheric oxygen. The precipitate was thoroughly washed by decantation and then treated with slightly less than the stoichiometric quantity of ethylenediaminetetraacetic acid, H4Y, and the pH of the mixture adjusted to about 8.5 with NaOH. The remaining Fe(0H)a was removed by filtration and the filtrate adjusted to pH 5 by addition of acetic acid and sodium acetate in appropriate quantities to give a total acetate concentration of 18’ and a concentration of F e y - of about 0.1F. \
,
After several days’ standing, such solutions yielded large brown-colored crystals of NaFeY .3H20which were collected by filtration, washed with ethanol and ether, and air dried. Purity of the crystals was confirmed by thin layer electrochemical analysis of weighed portions. Solutions of Fey-* were prepared by potentiostatic reduction of F e y - at a large platinum gauze electrode in the absence of oxygen. Other chemicals were reagent grade and were used without further purification. The water was triply distilled; the second distillation was from alkaline permanganate. The special micropipets employed have been previously described (8). RESULTS AND DISCUSSION
COY and COY-’. The single-cycle thin layer current potential curve for reduction of COY- followed by oxidation of COY-2 in 1P NaC104 supporting electrolyte is curve d in Figure 1. The great irreversibility of this couple observed in the earlier studies ( I , 2 ) persists even under thin layer conditions, although the much lower current densities prevailing in the thin layer cell produce anodic shifts in the potential at which COY- is reduced. Addition of iodide ion to the solution causes the electrode reactions to become more nearly reversible, as shown in curve B in Figure 1. This effect is believed to result from the preferential adsorption of iodide ion on the electrode leading to desorption of the cobalt complexes which, when adsorbed, interfere with the electrode reactions ( I , 2 ) . This ability of iodide ion both to desorb the cobalt complexes and to render the electrode reactions more reversible was exploited to measure VOL 38, NO. 1 1 , OCTOBER 1966
1601
