ranges and products of decomposition and interaction, it will probably be most useful for the study of polymeric materials and natural products. It should be possible to study large repeating units rather than just the simplest ultimate pyrolysis products. Some pilot work has been done on lignin and humus, and a larg: number of interesting products has been detected in addition to the expected series of aromatic compounds. Because no thermal cmductivity, flame ionization, or other detector is used, it is not necessary to use specific carrier gases for best results. Mechs nisms and interactions can be studied in any gas or vapor system-e.g., oxygen, air, nitrogen, helium, hydrogen, carbon dioxide, or mixtures containing water vapor, acids, ammonia, etc. Collection efficiency is surprisingly good; the band of products on the plate is sharply defined. The plate must, however, be decoupled from the heat of the furnace as much
as possible. Metal plates and/or efficient cooling may be necessary for operation at temperatures much higher than 500" C. The apparatus has been operated to 1000" C, but borosilicate glass plates had to be used, and it is believed that collection efficiency was appreciably reduced at the higher temperatures. ACKNOWLEDGMENT
The author thanks M. J. Naranjo for considerable help with thin layer chromatographic work and L. E. Edwards for design of the plate holder trolley. RECEIVED for review March 1 3 , 1967. Accepted April 3, 1967. This work was performed under the auspices of the U. S. Atomic Energy Commission.
Separation of Californium from Curium and Berkelium from Cerium by IExtraction Chromatography Fletcher L. Moore artd Aart Jurriaanse' Analytical Chemistry i3ivision, Oak Ridge National Laboratory, Oak Ridge, Tenn,
An extremely simple method is described for the separation of californium(lll) from curium(ll1) and berkelium(lll) from cerium(ll1). The new method is based on extraction chromatography utilizing small Teflon columns containing di(2-ethylhexyl)orthophosphoric acid as the stationary phase. Excellent separations are achieved with dilute nitric acid eluents. Among the significant advantages of the system are room temperature operation, use of nonchloride media, relatively high flow rates, and applicability for glove box or hot cell work. Several useful analytical and process applications are discussed.
Two OF THE MORE DiFFIcuLT problems in transplutonium chemistry are the separation of californium from curium and berkelium from cerium. In highly radioactive solutions the bulk of curium and cerium must be removed from californium and berkelium, respectively, prior to precise nuclear measurements on the latter two elements. Current methods (1) used for these separations are based on ion exchange procedures which are cumbersome and time-consuming. An attractive modern technique for separating metal ions of close chemical similarity is that of extraction chromatography. This simple, versatile, multiplate process combines the simplicity of ion exchange with the selectivity of liquidliquid extraction. Cerrai (2) and Katykhin (3) recently published excellent reviews on extraction chromatography. Di(2-ethy1hexyl)ortliophosphoric acid (HDEHP) is an excellent solvent for I ntra-group separations of the trivalent Present address, South African Atomic Energy Board, Private Bag 256, Pretoria, Republic of South Africa. (1) G. H. Higgins, "The Radiochemistry of the Transcurium Elements," NAS-N.S.3031 (1960). (2) E. Cerrai, Chromatog. Rev., 6 , 129 (1964). (3) G. S. Katykhin, Zh. Analit. Khim., 20,615 (1965).
lanthanide or actinide ions ( 4 , 3,because separation factors are higher than those observed in ion exchange methods. Moreover, the high reaction rate of HDEHP with these ions affords relatively fast flow rates. Extraction chromatographic methods based on HDEHP for the separation of lanthanide tracers in mineral acid systems at elevated temperatures have been reported by several workers (2,6-10). In a definite advance Kooi (11, 12) and coworkers adapted the HDEHP-HCl system for the chromatographic separation of several transplutonium elements. He used siliconized kieselguhr as a support for the HDEHP. By performing elutions at 87" C and flow rates of one drop per 45 seconds, he successfullyseparated fractions containing americium-curium, berkelium, and californium. He has proposed the method for application in transplutonium element processing (13). For transplutonium element separations we have now extended the use of HDEHP in extraction chromatography to nitric acid systems, utilizing Teflon powder as an inert support. This new system is extremely simple, because it provides excellent separations of californium from curium and berkelium from cerium at room temperature with dilute nitric acid solutions at relatively high flow rates. (4) D. F. Peppard, G. W. Mason, J. L. Maier, and W. J. Driscoll, J . Inorg. Nucl. Chem., 4, 334 (1957). (5) D. F. Peppard, G. W. Mason, W. J. Driscoll, and R. Sironen, J . btorg. Nucl. Chem., 7 , 276 (1958). (6) E. Cerrai and C . Testa, J . Inorg. Nucl. Chem., 25, 1045 (1963). (7) T. B. Pierce and R. S.Hobbs, J . Chromatog., 12,74 (1963). ( 8 ) T. B. Pierce, P. F. Peck, and R. S . Hobbs, J . Chromatog., 12, 81 (1963). (9) J. W. Winchester, J . Chromatog., 10, 502 (1963). (10) R. J. Sochacka and S. Siekierski, J . Chromatog., 16, 376 (1964). (11) J. Kooi, R. Boden, and J. Wijkstra, J. Inorg. Nucl. Chem., 26, 2300 (1964). (12) J. Kooi and R. Boden, Radiochim. Acta, 3, 226 (1964). (13) J. Kooi, Radiochim. Acta, 5 , 91 (1966).
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15
Figure 1. Separation of P5*Cffrom 244Cm by extraction chromatography Column: 5 X 70 mm, 0.5M HDEHP-heptane on Teflon-6 powder (70-80 mesh), 23"C,flow rate = 5-6 drops per minute
Figure 2. Separation of 24gBkfrom 14Te by extraction chromatography
EXPERIMENTAL
Column: 5 X 70 mm, 0.5M HDEHP-heptane on Teflon-6 powder (70-80 mesh), 23" C, flow rate = 5-6 drops per minute
Apparatus. An internal sample methane proportional counter was used for fission, alpha, and beta counting at voltage settings of 2100, 2900, and 4300, respectively. A NaI well-type scintillation counter, 13/4X 2 inches, was used for gamma counting. A silicon diode detector (3 cm2) coupled to a 256-channel anaiyzer was used for alpha spectrometry. A glass tube, 5-mm i.d. and 150 mm in length was drawn to a tip a t one end. A small glass wool plug was inserted in the tube to retain the support. Reagents. Di(2-ethy1hexyl)orthophosphoric acid, 0.5M. Purify di(2-ethylhexyl)orthophosphoric acid (HDEHP, available from Union Carbide Chemicals Co., New York, N. Y.) by mixing gently for 3 minutes with an equal volume portion of ethylene glycol. If mixed too vigorously, the phase separation is poor. Repeat the treatment of the HDEHP twice with fresh portions of ethylene glycol. Separate the phases by centrifugation. The final purity of the HDEHP was 99.7z. Weigh 16.11 grams and dilute to 100 ml. with n-heptane. Inert Support. Teflon-6, polytetrafluoroethylene powder, is available in specially pre-sieved form (70-80 mesh) from Analytical Engineering Laboratories, Hamden, Conn. Column Preparation. Add 10 ml. of 0.5M HDEHPheptane to 8 grams of Teflon-6 powder in a I-oz glass bottle. Cap the bottle and shake vigorously for 1-2 minutes. Prepare columns from this mixture by the following procedure: By use of a medicine dropper, add to the glass tube the solvent-treated Teflon powder, 3-4 drops at a time. Tamp firmly after each addition with a glass rod, being careful to eliminate air bubbles. When the column is packed to a height of 70 mm, allow the excess solvent to drain off. Condition she column by passing 5-10 ml of the appropriate
eluent through it. A flow rate of 5-6 drops per minute is attained. The free column volume as measured with ls4Cs is about 9 drops (-0.5 ml). Such a column contains about 33 mg of HDEHP. Procedures. SEPARATION OF CALIFORNIUM FROM C U R I U M . Condition the column by passing 5 ml of 0.2M nitric acid through it. Adjust the sample solution to 0.1M nitric acid. Carefully pipet 0.2 ml of the sample onto the center of the column. Allow the solution to just absorb, and wash the micropipet once with 0.2M nitric acid. When the wash solution just reaches the top of the column, add 0.2Mnitric acid. Continue to elute at 5-6 drops per minute with 0.2M nitric acid. Discard the first 10 ml of eluate, which contains the curium. Add 4 M nitric acid to the column and collect the next 5 ml of eluate, which contains the californium, in a 5-ml volumetric flask. Mix well. Prepare suitable aliquots on stainless steel plates for fission and/or alpha measurements. Alternatively, one may count the prompt gamma rays from 252Cf (14). Clean the column with 5-10 ml of 4Mnitric acid. Maintain several ml of 0.2M nitric acid over the column prior to the next separation. SEPARATION OF BERKELIUM FROM CERIUM. Condition the column by passing 5 ml of 0.15M nitric acid through it. Adjust the sample solution to 0.1M nitric acid. Carefully pipet 0.2 ml of the sample onto the center of the column. Allow the solution to just absorb and wash the micropipet once with 0.15M nitric acid. When the wash solution just reaches the top of the column, add 0.15M nitric acid. Con-
734
ANALYTICAL CHEMISTRY
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(14) F. L. Moore and J. S . Eldridge, ANAL.CHEM.. 36, 808
(1964).
tinue to elute at 5-6 drops per minute with 0.15Mnitric acid. Discard the first 8 ml of eluate, which contains the cerium. Add 4M nitric acid to the column and collect the next 5 ml of eluate, which ccintains the berkelium, in a 5-ml volumetric flask. Mix well. The determination of 24gBkin this solution is readily completed by one of the conventional methods (15, 16). Clean the column with 5-10 ml of 4M nitric acid. Maintain several ml of 0.15M nitric acid over the column prior to the next separation. RESUL,TS AND DISCUSSION
Teflon powder was selected as the inert support because of its exceptional. stability to chemical reagents and solvents. Teflon is strongly hydr,ophobic and readily retains a layer of organic extractant, wh..chforms the stationary phase. Unlike the inorganic supports which require special pretreatment to render them hydrophobic, Teflon-6 powder is ready for use as received from the manufacturer. The advantages of Teflon powder over various other supports in extraction chromatography have been discussed by Preobrazhenskii and Katykhin(17). Preliminary experiments were performed to evaluate the pertinent variables in the Teflon-HDEHP system Nitric acid was selected as the eluent, because of its compatibility with stainless steel. Excellent separations of californium from curium were e Tected by extraction chromatography utilizing Teflon-6 powder supporting heptane solutions of 0.02M, 0.10M, 0.50M', or 1.OM HDEHP with various dilute nitric acid eluents. The system, 0.5M HDEHP-heptane0.2M HNO, was selected for the standard procedure; lower concentrations of H D EHP readily become overloaded. With 0.5M HDEHP as the stationary phase, nitric acid concentrations greater than 0.2M eluted the californium too fast; on the other hand, nitric acid concentrations less than 0.2Meluted the curiurn too slowly. Pretreatment of the 0.2M nitric acid eluent with 0.5M HDEHP-heptane did not significantly change the elution pattern. Eluents at 60" C gave no appreciable improvement over those used at ambient temperature. Higher temperatures were not investigated because of the mechanical problems caused by bubbles. Several experiment!; were performed in which the height of the column was varied. As expected, a 30-mm column resulted in faster elution of the curium and a 100-mm column exhibited slower elution of the curium. In both cases, quantitative separations of curium from californium were achieved. Elution patterns with comparable hydrochloric acid solutions were essentially identical to those obtained with nitric acid eluents. Hydrochloric acid is less desirable than nitric acid for practical wcrk because of its corrosion properties. The nitric acid concentration of the sample aliquot loaded onto the column was not critical in the range, 0.02-0.20N. Although 0.2 ml. of sample was used in most of the work, sampie sizes of 1 ml and 5 ml gave excellent separations. In the latter KWOcases, the curium elution curve peaked later than in the former case. The normal flow rate obtained with the standard 5 X 70 mm coiumn was 5-6 drops (-0.35 ml) per min. Such a relatively (15) D I-. Peppard, J W. Moline, and G . U . Mason, J . lnorg. Nuc! C'hern., 4, 344 (1957 (16) F. L. Moore, AWL. CHFM.. 38, lh:2(1966 (17) E;. Preobrazhenskii and C S. Katykhin. Kadiokhirniya, 4. '31. (1 967'
Table I. Recovery and Decontamination of 252Cf as Function of Eluate Volume Found in ISzCfProduct (4M "0s) 0.2M HNOa Eluate, ml Z62Cf 2 * 'Crn 10 12
98.9 96.0
0.06
