EUWARD H. CARTER,JR., AND HILTON A. SMITH
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Vol. 67
THE SEPARATION OF HYDROGEK, HYDROGEN DEUTERIDE, TRITIUM HYDRIDE, DEUTERIUXS, TRITIUM DEUTERIDE, AND TRITIUM MIXTURES BY GAS CHROMATOGRAPHY BY EDWARD H. CARTER,JR., AND HILTON A. SMITH Department o~fChemistry, The University of Tennessee, Knoxville, Tennessee Received January 11, 1963 The resolution and analysis of the components in hydrogen-deuterium-tritium mixtures have been accomplished by gas chromatography a t 77°K. Tritium was incorporated into the sample mixtures in tracer quan2 X IO-' mc. per standard ml.). Helium, hydrogen, and neon were employed as carrier tities (ATT, = gases with several columns containing activated alumina and ferric oxide on alumina. Varying degrees of isotope separation were observed with different carriers, adsorbents, and conditions of column activation. Separation factors for the hydrogen isotopes and isomers on various columns a t 77°K. were calculated. Flow-modified ionization chambers and a Cary Model 31 vibrating reed electrometer equipped with a 10'0 (or 1011) ohm leak resistor were employed in series with thermistor-equipped katharometers for the detection of radioactive and non-radioactive hydrogen isotopes. Outputs from the electrometer and the katharometer were recorded simultaneously on two synchronized Brown electronic recorders. Simultaneous ionization chamber and katharometer detertion of para-hydrogen, ortho-hydrogen, hydrogen deuteride, and deuterium has been observed.
In recent years ~ ~ a r i o udegrees s of separation and analysis of hydrogen isotopes and isomers by gas chromatography have been reported.'-" These investigations, in general, have concentrated on the resolution of para-hydrogen, ortho-hydrogen, hydrogen deuteride, para-deuterium, and ortho-deuterium, or normal hydrogen, hydrogen deuteride, and normal deuterium without the inclusion of the radioactive hydrogen isotopes in the gas mixtures. Gant and Yang12have reported the resolution of hydrogen, tritium hydride, and tritium in gas mixtures rontaining approximately 1 atom per cent tritium on a molecular-sieve column at - 161O with helium carrier. Smith and C a r t e P have extended the resolution and analysis to mixtures containing tritium in tracer quantities (mole fraction T:! = on several columns with helium and hydrogen carriers at 77OK. With some modifications in previous techniquesI3 and equipment, the resolution and analysis of gas samples containing all of the various hydrogen isotopes and isomers, where tritium-containing components were present a t tracer levels, have been effected. Experimental Apparatus and Materials.-The essential features of the chromatographic and detector systems employed were as follows: The carrier gas from a tank was passed through a sampling system as shown in Fig. 1, thence through the chromatographic column followed immediately by a thermostated (25') katharometer, similar to that described by Thomas,l4 and a 50-ml. Borkowski ionization chamber, or interchangeable 5-ml. brass chamber, attached to a Cary Model 31 vibrating reed electrometer obtained from the Applied Physics Corporation, Monrovia, (1) C. 0. Thomas and H.
A. Smith, J. Phys. Chem., 63,427 (1959).
P. Hunt, ibid., 64, 383 (19601. (3) P. P. Hunt and €1. A. Smith, ibid,,66, 87 (1961). (4) W. R. Moore and H. R. Ward, J . Am. Chem. SOC.,80, 2909 (1958). (5) W. A. Van Hook and P. H. Emmett, J . Phvs. Chem., 64, 673 (1980). (6) 8. Ohkoshi, Y. Fujita, and T. Kwan, Bull. Chem. SOC.Japan, 31, 770 (1958); S. Ohkoshi, S. Tenma, Y. Fujita, and T. Kwan, zbsd., 31, 772 (1958); 5.Ohkoshi. S. Tenma, Y. Fujita, and T. Kwan, rbzd., 31, 773 (1958). (7) W. R. Moore and H. R. Ward, J. Phys. Chem., 64, 832 (1960). (8) T. Kwan, J. Res. Inst. Catalysts Japan, 8, 18 (1960). (9) S. Furuyama and T. Kwan, J . Phys. Chem., 66, 190 (1961). (10) F. Botter, G. Perriere. and S. Tistchenko, Cornm. Energie A t . (France), Rappt., CEB No. 1962 (1961). (11) L. Bachmann, E. Beohtold, and E. Cremer, J. Catalysts, 1, 113 (2) H. A. Smith and P.
(1962). (12) P. L.Gant and K. Yang, Science, 129, 1548 (1959). (13) H. A. Smith and E. H. Carter, Jr , "Proceedings of the International
Atomic Energy Agenoy Symposium on the Use of Tritium i n the Phyaisnl and Biological Sciencea," Vol. I, Vienna, Austria, 1962, pp, 121-L3aa (14) 0,0 , Thomas, J , Bhsm. E&&, 86, 617 (1858)8
California; thence through a flowmeter followed by an oxidizing unit to convert any hydrogen to water vapor and finally through a trap containing Linde Molecular Sieves (size 5A) a t Dry Iceacetone temperature. The katharometer and electrometer outputs were connected to synchronized Brown recording potentiometers. A leak resistor of 10'0 (or loll) ohms was installed in the electrometer head between the input terminal and the feedback line, thus allowing the use of a flow system for continuous monitoring of tritium activity emerging from the column. The reservoirs attached to the sample by-pass cell, as shown in Fig. 1, were used for the preparation of equilibrating or equilibrated mixtures of hydrogen-deuterium-hydrogen deuteride, hydrogen-tritium-tritium hydride, and deuterium-tritium-tritium deuteride. They consisted of 100-ml. glass bulbs carrying two tungsten leads which were brazed to coiled nichrome wire heating elements for isotope exchange equilibration. Various sample mixtures from these reservoirs -'ere injected, a t known pressure and volume, into the chromatographic column by diversion of the carrier gas stream through the sample by-pass cell. The tritium content of one-curie ampoules'3 of tritium containing 0.89 ml. of tritium a t 475 mm. pressure was expanded into evacuated metal cylinders of known volume and diluted with hydrogen, deuterium, helium, or neon to the desired tritium activity per standard ml. of gas (0.20-0.25 mc.) for use in the chromatographic experiments. The original mole ratios of tritium t o diluent in these gas mixtures were in the range 1.01.3 X However, since slow exchange of tritium-hydrogen and tritium-deuterium occurred in the metal reserve tanks, this figure, when corrected for radioactive decay, actually represented one-half the tritium hydride or tritium deuteride mole fraction plus the tritium mole fraction present a t any time. The following procedure, similar to that of Moore and VrTard,7 was used to prepare the ferric oxide on alumina columns: An 80-100 mesh cut of Grade F-20 activated alumina, obtained from the Aluminum Company of America, weighing 250 g. was covered with 400 ml. of a 2 M solution of ferric chloride in a 1-1. erlenmeyer flask. Stirring was carried out intermittently to allow adequate penetration of the alumina by the ferric chloride solution. After a 15-min. stirring period, 3 M aqueous ammonia was added to the slurry until ferric hydroxide precipitation was complete. Stirring was continued during this precipitation. The suspended material was then stirred thoroughly over a 1-hr. period and filtered. The ferric hydroxide precipitate adhered to, or coated, the alumina in this process. The filtered material was then washed several times with distilled water, transferred to an evaporating dish, and placed in a preheated oven a t 120" for 24 hr. The dried material was then crushed, rescreened to 80-100 mesh, and used to pack several 7-mm. diameter Pyrexcoiled columns of various lengths for use in the chromatography experiments. These columns were equipped with small standard-taper ball and socket joints for attachment to the apparatus. The uncoated activated alumina columns were prepared by packing various lengths of 7-mm. diameter Pyrex coils with 80100 mesh, Grade F-20, activated alumina. Each 601umx1, after installation inta tho Chromatography
July, 1963
SEPARATION OF HYDROGEN-DEUTERIUM-TRITIUM MIXTCRESBY GASCHROMATOGRAPHY1513
apparatus, was cooled to liquid nitrogen temperature (77 f 1OK.) in a 2-1. or 1-1. dewar flask for the elution experiments. Helium, hydrogen, and neon were employed as carrier gases. Helium, hydrogen, and deuterium have only slightly different thermal conductivities. This property necessitated operation of the katharometer circuit a t very high sensitivity for adequate detection of these gases in the presence of excess helium, or preliminary sample oxidation to water vapor prior to detection in the katharometer . For samples containing tritium activity, preliminary oxidation resulted in considerable loss in ionization chamber sensitivity to this activity, in comparison with unoxidized gas-phase detection, and produced considerable elution peak tailing for radioactive tritium components. Therefore unoxidized gas-phase detection of the isotopes was employed and adequate sensitivity to non-radioactive isotopes obtained by high-sensitivity operation of the katharometer circuit. Helium in a high state of purity was obtained from the Medical Gas Division of Welding Gas Products Company, Knoxville, Tennessee, and was used with and without purification with no resultant change in characteristic hydrogen and deuterium chromatograms. Purification was attempted by passage of the helium through a Linde Molecular Sieve (5A) trap cooled t o 77°K. Neon produces greater sensitivity to hydrogen and deuterium detection by change in thermal conductivity than does helium and can be employed as a carrier gas a t liquid nitrogen temperature. Research grade neon was obtained in a high state of purity from the Matheson Company, East Rutherford, New Jersey, and was used without further purification. Hydrogen was also used as a carrier gas. The hydrogen employed was obtained from Welding Gas Products Company, Knoxville, Tennessee, and was used with and without purification with no resultant change in characteristic deuterium chromatograms. Purification was identical to that employed with helium. Deuterium reported to be 99.570 pure was obtained from General Dynamics Corporation, San Carlos, California.
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Experimental Results and Conclusions Activated Alumina Columns.-With an 8-ft. activated alumina column varying degrees of column activity (dehydration) had a marked effect on the retention times and resolution of hydrogen isotopes. This effect is shown in Fig. 2 for the resolution of the radioactive hydrogen isotopes. As can be seen from an examination of the figure, a progressive increase in activation or dehydration produced an increase in the isotope separation. The method of column activation was unimportant but the final state of activation (extent of water removal) was extremely important and exhibited a n upper limit beyond which isotope retention times became prolonged and considerable band broadening was observed even with marked increase in carrier flow rate. Similar degrees of column activity to that, given for part C of Fig. 2 were obtained by column activation a t 370' for a period of 8 hr. under a low helium flow rate. Under the latter conditions of column activation, the alumina column was found to be effective in the resolution of hydrogen, tritium hydride, deuterium, tritium deuteride, and tritium, as shown in Fig. 3, with only partial equilibration of para-hydrogen and ortho-hydrogen observed a t the high column activity. The partial p-Ha & o-Hz interconversion was evidenced on alumina columns which had been extensively dehydrated. This phenomenon has been reported previously by Moore and Ward7and good agreement was found here. An interesting feature of the electrometer recorder traces for samples similar to that shown in Fig. 3 was evidenced upon conversion from the small-volume (5ml,) ion chamber to the larger-volume (50-ml.) BOT-. kowski chamber. A somewhat elevated background ~ Q K current I was exhikited by thhk chamber partly due t o
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Fig. 2.-Typical electrometer recorder traces for HZ Tz 2HT and Dz T2 2DT samples showing the effect of varying degrees of column activation on retention times and resolution of active components on the 8-ft. alumina column with helium carrier a t 77°K. Ion chamber, 5 ml., polarizing potential, - 135 v. Column activation prior to samples: (A) heated column in air to 138" for 48 hr. after complete deactivation with H20, then heated a t 200" for 3 hr. under vacuum; (B) part A, then heated in a gas-air flame under vacuum for 5 min.; (C) parts A and B, then heated in gas-air flame under vacuum for 10 min.
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its inherently greater sensitivity to small residual ion currents and also to a pretreatment procedure with a neon-tritium sample having an activity of 2.45 x 10-1
1,514
EDWARD H. CARTER, JR.,AND HILTOSA. SMITH
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Fig. 4.--Typical electrometer recorder trace for H,-HT-D,IIT-T, sample mixture ( 5 . 2 3 std. ml.) with helium carrier at a flow rate of 100 ml./min. through an 8-ft. activated (370°, 8 hr.) alumina column at 77°K. Ion chamber, 50 ml., polarizing potential, -135 v.
me. per standard mI. Under these conditions resolution of hydrogen, tritium hydride, deuterium, tritium deuteride, and tritium jyas evidenced aiid adequate detection of both radioactive and non-radioactive hydrogen isotopes mas observed with the ion chamber and electrometer as shown in Fig. 4. The small-r~olume chamber did not exhibit this property. Hydrogen and deuterium detection sensitivity on the electrometer has been investigated aiid seenis to be a function of the background activity level in the ion chamber. The higher the background ion current, up amp., the greater was to a maximum of about 1 X this detection sensitivity. However, no appreciable difference in hydrogen aiid deuterium detection was observed for equivalent samples eluted at various background levels in the range to 10-l1 amp. ,4t backgrounds below or amp. this sensitivity decreased. These measurements, of course, were observed at a fixed electrometer sensitivity. At higher electrometer sensitivities adequate detection of hydrogen and/or deuterium elution was obtained even a t residual ion current levels as low as amp. For a given electrometer setting this detection characteristic was reduced considerably by prolonged evacuation and heating of the ion chamber. This procedure, applied over a 24-hr. period, reduced the residual ion current in the chamber to about 10-l5 amp. With the small-volume chamber this detection did not occur appreciably, though it could be induced slightly with high background activities (200-400 pc. in the form of labeled nonadecanoic acid deposited on a copper plate attached to the inner wall of the chamber) and high ion-current sensitivities on the electrometer. With hydrogen as the carrier gas, no detection of deuterium and/or hydrogen deuteride was observed on the electrometer. With neon carrier, ion-chamber elution of hydrogen and deuterium was indicated but a t considerably decreased sensitivity to that observed with helium carrier. Adequate detection sensitivity to nonradioactive isotope elution by the 50-ml. chamber with helium carrier occurred in every instance where the reamp. Residual ion current was >, 10-l2 or sidual ion currents greater than amp. were impractical since high electrometer sensi"ivities were necessitated for adequate detection of $e tritium concentra-
