- Email: [email protected]
Use of nitrilotriacetic acid and different retaining ions in the separation of rare earths in tracer scale by ion exchange
Technical Acknowledgements-We are grateful to our colleagues from the three centres for many fruitful discussions. One of us (H.A.K.) is grateful to Pakistan Atomic Energy Commission for allowing him to participate in this collaborative programme. Nuclear Engineering Division HAMEED AHMED KHAN Pakistan Institute of Nuclear Science and Technology (PINSTECH) Nilore, Rawalpindi Pakistan Nuclear Research Laboratory Government College Lahore, Pakistan
M. AFZAL P. CHAUDHARY S. MUBARAKMAND
Pakistan Atomic Energy Mineral Centre Lahore, Pakistan Physics Department, Gomal University, D.I. Khan, Pakistan
F. I. NAGI
ABDUL WAHID
References 1. Proc. IAEA Conf. ‘Radon in Uranium Mining’, No. IAEA-PL-56518 (1974). 2. THOMPKINS R. W. Can. Min. J. 91, 103 (1970). 3. FLEISCHEFCR. L., PRICE P. B. and WALKER R. M. In Nuclear Tracks in Solids-Principles and Applications. University of California Press, Berkeley (1975). 4. KHAN H. A. Nucl. Instrum. Meth. 113, 55 (1973). 5. KHAN H. A. Nucleus (Karachi) 8, 63 (1971).
!nternat~onal Journalof AppliedRadiatmnand Isotopes.1977 Vol. 28. pp. 731-732. Pcrgamon Press. Printed in GreatBritain
Use of Nitrilotriacetic Acid and Different Retaining Ions in the Separation of Rare Earths in Tracer Scale by Ion Exchange (Received 1 February
notes
731
almost linear increase is actually known to occur in case of nitrilotriacetic acid (NTA) though the absolute differences in the value in the lightest and the heaviest rare earths are not much as is observed in case of EDTA.” Hence NTA has earlier been proposed also as a good eluting agent for the rare earths’2-6’ and several retaining ions have been used at random for the purpose.‘7-14’ But no systematic work has so far been carried out in this system. A preliminary investigation in this regard is therefore reported here.
Experimental Materials All chemicals used in the investigation were of analytical reagent grade. Dowex 5OW-X8 (2@50 mesh, H’ form) was initially used from which the resins in various ionic forms were prepared in the usual way. Disodium salt of nitrilotriacetic acid (Na-NTA) was used as the eluting agent. The radioactive isotopes, e.g. ‘41Ce(32.5 days), “%rn (47 hr), 16’Tb(71 days) and “‘Tm(l27 days) of high specific activity were procured from BARC, Trombay, in hydrochloric acid medium and were used as the representative rare earths. The radioactive solutions were diluted according to the requirements. Procedure After the column was conditioned, the required amount of tracers in hydrochloric acid medium (- 2 N) were transferred to the top of the resin column where it had been adsorbed and then the column was washed with water. The elution was then carried out by allowing Na-NTA solution of desired concentration to percolate through the column. Fractions (1 ml) of effluent at a flow rate of 15 drops/min were collected successively during the entire course of elution. The activity present in each fraction was then determined.
Results and Discussion To test the possibility of separation of rare earths, a mixture of rare earths, not too much apart from each other, such as “‘Tm, r6’Tb, ‘?Sm and 14rCe were taken. The pH of the eluting solution was taken as 6.5, which was found to be most effective in giving reproducible
1977)
A mixture of rare earth tracers, e.g. “‘Tm, “‘Tb, ‘%m and r4’Ce was adsorbed on a Dowex 5OW-X8 cation . exchange column and elutron was then carried out by using 1% solution of disodium salt of nitrilotriacetic acid at pH 6.5. The effect of the use of various mono- and divalent ions as the retaining ions was studied and it was found that Cs+ and CdZ+ ions amongst them appear to be most effective.
Introduction THE use of aminopolycarboxylic
acids as eluting agents for the separation of rare earths adsorbed on a cation exchange column is well known. The efficiency of separation of the successive rare earths is obviously determined by the differences in stability constants of their relevant complexes. The stability constants usually increase with the increase of the atomic number of the rare earth. An
Volume,
FIG. 1. Elution
ml
curve of “‘Tm, 16’Tb, r5%rn and r4rCe with 1% Na-NTA solution at pH 6.5. Column: 9 x 0.5 cm. Dowex 5OW-X8 (20-50 mesh, Na+-form); flow rate: 15 drops/min.
732
Technical
notes
“‘)lb)
Volume,
ml
FIG. 2. Elution curves of “‘Tm with 1% Na-NTA solution at pH 6.5 using (a) Cs+-, (b) Rb+-, (c) K’-, (d) NH:-. (e) Na+- and (I) Li+-forms of Dowex 5OW-X8 (2C-50 mesh) resin column of 9 x 0.5 cm at a flow rate of 15 drops/min.
results. The composition of the elutmg solution was varied, e.g. 0.5, 1.O and 1.5%. The change in concentration of the eluent has actually a large effect on the elution profile. At lower concentration of the eluent, unusually a longer time and a comparatively large volume of eluent will be required for the elution of the tracer. At higher concentration of the eluent again the peaks become very closer and the possibility of overlapping of peaks becomes imminent if the number of elements are large, making the separation almost impracticable. However, if the number of rare earth elements is comparatively small, a solution of higher concentration may be used whereby the separation would be quicker in comparison. Figure 1 shows the elution curve for the four representative rare earths when the eluent comprises a solution of 1% Na-NTA at pH 6.5. It is needless to stress here that factors such as flow rate, concentration of the eluent, nature of the retaining ions, etc. are important while considering the separation of a large number of rare earth by the same method. The importance of the nature of the retaining ions has already been stressed. The effect of a series of mono- and divalent cations has been stlldied in the present investigation and “‘Tm has been used as the representative of rare earth elements. It is evident from Fig. 2 that in case of the monovalent ions the amount of eluent required for removal of “‘Tm gradually decreases with increasing size of the cationic species. A similar behaviour was also observed in case of divalent ions, as is evident from Fig. 3. The experimental orders of cation affinities towards the resin in the present system are therefore; Li+ < Na+ < NH: < K+ < Rb+ < Cs+ for univalent ions; and Zn’+ < Ni’+ < Cu*+ < Co’+ < Cd’+ for bivalent ions. This observed order of affinities is also in agreement wi!h the known order of selectivity of the respective ions.‘lS’ Moreover, in the case of divalent ions, the amount of eluent required for maximum elution of the rare earth is larger than in case of monovalent ions, and this is also in agreement with that of the general trend of bond strengths between the ions of different charges and the ionexchangers. From the aforesaid results it can then be concluded that amongst the monovalent and divalent ions,
FIG. 3. Elution curves of “‘Tm with 1”” Na-NTA solution at pH 6.5 using (a) Cd*+-, (b) Co”-, (c) Cu2+-, (d) Nil ‘and (e) Zn*+-forms of Dowex 5OW-X8 (20-50 mesh) resm column of 9 x 0.5 cm at a flow rate of 15 drops/min
Cs+ and Cd” forms of resin, respectivelJ will be most suitable for effecting the separation in question since these require minimum amount of eluent to remove the tracer and in both cases tailing is much less compared to that in case of others. Nuclear Chemistry Division, N. R. DAS Saha Institute of Nuclear Physics S. N. BHATTACHARYYA 92, Acharya Prafulla Chaudra Road, Calcutta-700001. India.
References 1. POWELL J. E. and SPEDDING F. H. Trans. AIME 215, 457( 1959). 2. FITCH F. T. and RUSSELL D. S. Can. J. Chem. 29, 363(1951). 3 BECK G. He/u. chim. Acra 29, 357(1946). 4. BECK G. and GA~SER A. Anal. chim. Actu 3, 41(1949). 5. SCHWARZENBACK G., KAMPITSCH E. and STEINER R. He/u. chim. Acta 28, 828(1945). 6. MI~ROFANOVA N. D., MARTYNENKO L. I. and PEROVA I. N. Russ. J. Phys. Chem. (Engl. Transl.) 47 (2). 187(1973). 7. HOLLECK L. and HARTINGER L. Angew. Chem. 68, 41 l(1956). 8. TOPP N. E. Chemy fnd. 1320(1956). 9. WOLF L. and MASSONE J. Chem. Teck. (Berlin) 10, 290(1957). 10. NODDACK W. and OERTEL G. Z. Electrochem. 61, 1216(1957). 11. WEIDMANN G. and LIEBOLD G. Angew. Chem. 69, 753(1957). 12. FRANK B. Annls Uniti. Mariae Curie-Sklodowska Section AA, 2627. 255(1971).
Technical 13. HGRICHE W.. FRANK B. and WYSOCK L. J. ibid. 26-21. 223. 235, 241 (1971). 14. LORIERS J. and CARMINATID. C.r. Hebd. Sdanc. Acad. Sci., Paris 237. 1328(1953). 15. KRESSMAN T. R. E. and KITCHENER J. A. J. chum Sot. 1190. 1201. 1208, 1211 (1949).
lnter~~at~onal Journal of Appkd Radiation and Isotopes. pp 733-135 Pergamon Press. Punted in Great Britain
1977. Vol.
2.
A Single Solvent Cocktail for Liquid Scintillation Counting of Tritium in Aqueous Samples MEASUREMENTof tritium m aqueous solutions is usually carried out by liquid scintillation counting in emulsifying “cocktails”, using one of several commercial or “homemade”“-” cocktail mixtures. Thus, we have explored the practicality of using the surfactant Triton X-100* as the only solvent. following the observation by TURNER(~) that It can function as a primary scintillation solvent. although giving solutions with lower counting efficiency than the usual toluene-Triton mixtures. Preliminary experiments indicated that satisfactory cocktails could be made from purified”’ Triton X-100 and
* Triton X-100 is the trademark name of Rohm & Haas. Ltd. for isoctylphenoxypolyethoxyethanol.
TABLE I. Effects of additives
on the tritium
733
notes
various commercially available fluors. A mixture of PPO and POPOP was more effective than the other combinations tested. Using O.lOg POPOP/l cocktail the tritlum counting efficiency increases with PPO concentration to a maximum at 9g/l. then decreases slowly at higher concentrations. Ten g of PPO was chosen as a practical quantity for subsequent tests. Using a standard 15-m] volume of this cocktail (10 g of PPO and 0.1 g POPOP/l purified Triton X-100) with differing volumes of tritiated water. we confirmed that the countmg efficiency of the resulting homogeneous solutions IS a smooth function of the amount of aqueous solution added and has adequate efficiency (7 -19”“) in the range from 0 to 5 ml of added aqueous treated solution. The effects of various additives upon counting efficiency are indicated in Table 1. Although the efficiency is not affected by salt or sucrose. it drops rapidlq with additions of acid or base. particularly when the larger volume is used. The very large drop associated with addition of sodium hydroxide is at least partly attributable to color quenching. The great capacity of Trlton X-IO&water solutions to dissolve or solubilize salts suggested the addition of a buffer salt to the cocktail to stabilize it for use with acidic or basic samples. Figure I shows the counting effciences of samples made by placing in a hquid scintillation vlal: no, 0.25 g or 0.50 g of ammonium acetates. 15 ml of cocktail and 5 ml of tritiated solutions of HCI or NaOH, followed by heating (to CN. 50°C) and shaking for ca. IOsec to give an apparent homogeneous phase. The simple cocktail, without added buffer. is not satisfactory for general use with acidic or basic aqueous solutions, but 0.25 or 0.5Og of ammonium acetate stabilizes the system over practical ranges of acid or base concentrations. counting
efficiency
of unbuffered
cocktail*
Volume Of
Aqueous phase H,O 0.9”’ NaCl 0.1 ‘b HCI I .O M HCI 0.1 M NaOH I .O M NaOH 3072 sucrose H,O 0.9% NaCl 0.1 M HCI l.OM HC1 0.1 M NaOH 1.0 M NaOH 300/, sucrose
aqueous phaset (ml) 1
I I I
I 1 1 5 5 5 5 5 5 5
Appearance of solution csp!? csp csp csp light yellow yellow csp csp csp csp csp yellow yellow csp
Counting efficiency (c.p.m./d.p.m.)f 0.134 0.134 0.131 0.110 0.121 0.032 0.138 0.073 0.072 0.063 0.036 0.029 0.004 0.077
Efficiency relative to water I.00 1.00 0.9x 0.82 0.90 0.24 I .03
1.oo 0.99 0.86 0.49 0.40 0.06 I .05
* Cocktail composition : 10 g PPO, 0.1 g POPOP, 1 1. purified Triton X-100. t Counting samples made by adding 0.100 ml of tritiated water and 0.90 (or 4.90) ml of test solution to 15.0ml of cocktail, then homogenizing the solutions by heating to ca. 50°C and shaking for 10 sec. $Samples were counted at lGl2”C using a Philips Model PW 4510 automatic liquid scmtillation analyzer. $ tsp. colorless single phase. &I(.,
2X/R-
D
M. AFZAL P. CHAUDHARY S. MUBARAKMAND
Pakistan Atomic Energy Mineral Centre Lahore, Pakistan Physics Department, Gomal University, D.I. Khan, Pakistan
F. I. NAGI
ABDUL WAHID
References 1. Proc. IAEA Conf. ‘Radon in Uranium Mining’, No. IAEA-PL-56518 (1974). 2. THOMPKINS R. W. Can. Min. J. 91, 103 (1970). 3. FLEISCHEFCR. L., PRICE P. B. and WALKER R. M. In Nuclear Tracks in Solids-Principles and Applications. University of California Press, Berkeley (1975). 4. KHAN H. A. Nucl. Instrum. Meth. 113, 55 (1973). 5. KHAN H. A. Nucleus (Karachi) 8, 63 (1971).
!nternat~onal Journalof AppliedRadiatmnand Isotopes.1977 Vol. 28. pp. 731-732. Pcrgamon Press. Printed in GreatBritain
Use of Nitrilotriacetic Acid and Different Retaining Ions in the Separation of Rare Earths in Tracer Scale by Ion Exchange (Received 1 February
notes
731
almost linear increase is actually known to occur in case of nitrilotriacetic acid (NTA) though the absolute differences in the value in the lightest and the heaviest rare earths are not much as is observed in case of EDTA.” Hence NTA has earlier been proposed also as a good eluting agent for the rare earths’2-6’ and several retaining ions have been used at random for the purpose.‘7-14’ But no systematic work has so far been carried out in this system. A preliminary investigation in this regard is therefore reported here.
Experimental Materials All chemicals used in the investigation were of analytical reagent grade. Dowex 5OW-X8 (2@50 mesh, H’ form) was initially used from which the resins in various ionic forms were prepared in the usual way. Disodium salt of nitrilotriacetic acid (Na-NTA) was used as the eluting agent. The radioactive isotopes, e.g. ‘41Ce(32.5 days), “%rn (47 hr), 16’Tb(71 days) and “‘Tm(l27 days) of high specific activity were procured from BARC, Trombay, in hydrochloric acid medium and were used as the representative rare earths. The radioactive solutions were diluted according to the requirements. Procedure After the column was conditioned, the required amount of tracers in hydrochloric acid medium (- 2 N) were transferred to the top of the resin column where it had been adsorbed and then the column was washed with water. The elution was then carried out by allowing Na-NTA solution of desired concentration to percolate through the column. Fractions (1 ml) of effluent at a flow rate of 15 drops/min were collected successively during the entire course of elution. The activity present in each fraction was then determined.
Results and Discussion To test the possibility of separation of rare earths, a mixture of rare earths, not too much apart from each other, such as “‘Tm, r6’Tb, ‘?Sm and 14rCe were taken. The pH of the eluting solution was taken as 6.5, which was found to be most effective in giving reproducible
1977)
A mixture of rare earth tracers, e.g. “‘Tm, “‘Tb, ‘%m and r4’Ce was adsorbed on a Dowex 5OW-X8 cation . exchange column and elutron was then carried out by using 1% solution of disodium salt of nitrilotriacetic acid at pH 6.5. The effect of the use of various mono- and divalent ions as the retaining ions was studied and it was found that Cs+ and CdZ+ ions amongst them appear to be most effective.
Introduction THE use of aminopolycarboxylic
acids as eluting agents for the separation of rare earths adsorbed on a cation exchange column is well known. The efficiency of separation of the successive rare earths is obviously determined by the differences in stability constants of their relevant complexes. The stability constants usually increase with the increase of the atomic number of the rare earth. An
Volume,
FIG. 1. Elution
ml
curve of “‘Tm, 16’Tb, r5%rn and r4rCe with 1% Na-NTA solution at pH 6.5. Column: 9 x 0.5 cm. Dowex 5OW-X8 (20-50 mesh, Na+-form); flow rate: 15 drops/min.
732
Technical
notes
“‘)lb)
Volume,
ml
FIG. 2. Elution curves of “‘Tm with 1% Na-NTA solution at pH 6.5 using (a) Cs+-, (b) Rb+-, (c) K’-, (d) NH:-. (e) Na+- and (I) Li+-forms of Dowex 5OW-X8 (2C-50 mesh) resin column of 9 x 0.5 cm at a flow rate of 15 drops/min.
results. The composition of the elutmg solution was varied, e.g. 0.5, 1.O and 1.5%. The change in concentration of the eluent has actually a large effect on the elution profile. At lower concentration of the eluent, unusually a longer time and a comparatively large volume of eluent will be required for the elution of the tracer. At higher concentration of the eluent again the peaks become very closer and the possibility of overlapping of peaks becomes imminent if the number of elements are large, making the separation almost impracticable. However, if the number of rare earth elements is comparatively small, a solution of higher concentration may be used whereby the separation would be quicker in comparison. Figure 1 shows the elution curve for the four representative rare earths when the eluent comprises a solution of 1% Na-NTA at pH 6.5. It is needless to stress here that factors such as flow rate, concentration of the eluent, nature of the retaining ions, etc. are important while considering the separation of a large number of rare earth by the same method. The importance of the nature of the retaining ions has already been stressed. The effect of a series of mono- and divalent cations has been stlldied in the present investigation and “‘Tm has been used as the representative of rare earth elements. It is evident from Fig. 2 that in case of the monovalent ions the amount of eluent required for removal of “‘Tm gradually decreases with increasing size of the cationic species. A similar behaviour was also observed in case of divalent ions, as is evident from Fig. 3. The experimental orders of cation affinities towards the resin in the present system are therefore; Li+ < Na+ < NH: < K+ < Rb+ < Cs+ for univalent ions; and Zn’+ < Ni’+ < Cu*+ < Co’+ < Cd’+ for bivalent ions. This observed order of affinities is also in agreement wi!h the known order of selectivity of the respective ions.‘lS’ Moreover, in the case of divalent ions, the amount of eluent required for maximum elution of the rare earth is larger than in case of monovalent ions, and this is also in agreement with that of the general trend of bond strengths between the ions of different charges and the ionexchangers. From the aforesaid results it can then be concluded that amongst the monovalent and divalent ions,
FIG. 3. Elution curves of “‘Tm with 1”” Na-NTA solution at pH 6.5 using (a) Cd*+-, (b) Co”-, (c) Cu2+-, (d) Nil ‘and (e) Zn*+-forms of Dowex 5OW-X8 (20-50 mesh) resm column of 9 x 0.5 cm at a flow rate of 15 drops/min
Cs+ and Cd” forms of resin, respectivelJ will be most suitable for effecting the separation in question since these require minimum amount of eluent to remove the tracer and in both cases tailing is much less compared to that in case of others. Nuclear Chemistry Division, N. R. DAS Saha Institute of Nuclear Physics S. N. BHATTACHARYYA 92, Acharya Prafulla Chaudra Road, Calcutta-700001. India.
References 1. POWELL J. E. and SPEDDING F. H. Trans. AIME 215, 457( 1959). 2. FITCH F. T. and RUSSELL D. S. Can. J. Chem. 29, 363(1951). 3 BECK G. He/u. chim. Acra 29, 357(1946). 4. BECK G. and GA~SER A. Anal. chim. Actu 3, 41(1949). 5. SCHWARZENBACK G., KAMPITSCH E. and STEINER R. He/u. chim. Acta 28, 828(1945). 6. MI~ROFANOVA N. D., MARTYNENKO L. I. and PEROVA I. N. Russ. J. Phys. Chem. (Engl. Transl.) 47 (2). 187(1973). 7. HOLLECK L. and HARTINGER L. Angew. Chem. 68, 41 l(1956). 8. TOPP N. E. Chemy fnd. 1320(1956). 9. WOLF L. and MASSONE J. Chem. Teck. (Berlin) 10, 290(1957). 10. NODDACK W. and OERTEL G. Z. Electrochem. 61, 1216(1957). 11. WEIDMANN G. and LIEBOLD G. Angew. Chem. 69, 753(1957). 12. FRANK B. Annls Uniti. Mariae Curie-Sklodowska Section AA, 2627. 255(1971).
Technical 13. HGRICHE W.. FRANK B. and WYSOCK L. J. ibid. 26-21. 223. 235, 241 (1971). 14. LORIERS J. and CARMINATID. C.r. Hebd. Sdanc. Acad. Sci., Paris 237. 1328(1953). 15. KRESSMAN T. R. E. and KITCHENER J. A. J. chum Sot. 1190. 1201. 1208, 1211 (1949).
lnter~~at~onal Journal of Appkd Radiation and Isotopes. pp 733-135 Pergamon Press. Punted in Great Britain
1977. Vol.
2.
A Single Solvent Cocktail for Liquid Scintillation Counting of Tritium in Aqueous Samples MEASUREMENTof tritium m aqueous solutions is usually carried out by liquid scintillation counting in emulsifying “cocktails”, using one of several commercial or “homemade”“-” cocktail mixtures. Thus, we have explored the practicality of using the surfactant Triton X-100* as the only solvent. following the observation by TURNER(~) that It can function as a primary scintillation solvent. although giving solutions with lower counting efficiency than the usual toluene-Triton mixtures. Preliminary experiments indicated that satisfactory cocktails could be made from purified”’ Triton X-100 and
* Triton X-100 is the trademark name of Rohm & Haas. Ltd. for isoctylphenoxypolyethoxyethanol.
TABLE I. Effects of additives
on the tritium
733
notes
various commercially available fluors. A mixture of PPO and POPOP was more effective than the other combinations tested. Using O.lOg POPOP/l cocktail the tritlum counting efficiency increases with PPO concentration to a maximum at 9g/l. then decreases slowly at higher concentrations. Ten g of PPO was chosen as a practical quantity for subsequent tests. Using a standard 15-m] volume of this cocktail (10 g of PPO and 0.1 g POPOP/l purified Triton X-100) with differing volumes of tritiated water. we confirmed that the countmg efficiency of the resulting homogeneous solutions IS a smooth function of the amount of aqueous solution added and has adequate efficiency (7 -19”“) in the range from 0 to 5 ml of added aqueous treated solution. The effects of various additives upon counting efficiency are indicated in Table 1. Although the efficiency is not affected by salt or sucrose. it drops rapidlq with additions of acid or base. particularly when the larger volume is used. The very large drop associated with addition of sodium hydroxide is at least partly attributable to color quenching. The great capacity of Trlton X-IO&water solutions to dissolve or solubilize salts suggested the addition of a buffer salt to the cocktail to stabilize it for use with acidic or basic samples. Figure I shows the counting effciences of samples made by placing in a hquid scintillation vlal: no, 0.25 g or 0.50 g of ammonium acetates. 15 ml of cocktail and 5 ml of tritiated solutions of HCI or NaOH, followed by heating (to CN. 50°C) and shaking for ca. IOsec to give an apparent homogeneous phase. The simple cocktail, without added buffer. is not satisfactory for general use with acidic or basic aqueous solutions, but 0.25 or 0.5Og of ammonium acetate stabilizes the system over practical ranges of acid or base concentrations. counting
efficiency
of unbuffered
cocktail*
Volume Of
Aqueous phase H,O 0.9”’ NaCl 0.1 ‘b HCI I .O M HCI 0.1 M NaOH I .O M NaOH 3072 sucrose H,O 0.9% NaCl 0.1 M HCI l.OM HC1 0.1 M NaOH 1.0 M NaOH 300/, sucrose
aqueous phaset (ml) 1
I I I
I 1 1 5 5 5 5 5 5 5
Appearance of solution csp!? csp csp csp light yellow yellow csp csp csp csp csp yellow yellow csp
Counting efficiency (c.p.m./d.p.m.)f 0.134 0.134 0.131 0.110 0.121 0.032 0.138 0.073 0.072 0.063 0.036 0.029 0.004 0.077
Efficiency relative to water I.00 1.00 0.9x 0.82 0.90 0.24 I .03
1.oo 0.99 0.86 0.49 0.40 0.06 I .05
* Cocktail composition : 10 g PPO, 0.1 g POPOP, 1 1. purified Triton X-100. t Counting samples made by adding 0.100 ml of tritiated water and 0.90 (or 4.90) ml of test solution to 15.0ml of cocktail, then homogenizing the solutions by heating to ca. 50°C and shaking for 10 sec. $Samples were counted at lGl2”C using a Philips Model PW 4510 automatic liquid scmtillation analyzer. $ tsp. colorless single phase. &I(.,
2X/R-
D