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In the gas exposure technique for tritium labeling [1], organic compounds are exposed to curie amounts of tritium gas for several days. The energy released in the disintegration of the tritium and absorbed in the system provides the activation necessary to effect labeling. Since appreciable quantities of energy, 1.8·1019 ev per curie-day of tritium, are involved, some radiation damage occurs. The products of radiation damage may contain an appreciable fraction of the organically bound tritium and may have a high specific activity. Efficient purification procedures will generally be required to obtain the parent compound radiochemically pure. The concentration of tritium which can be introduced into a compound is limited by its sensitivity to radiation damage, but for many compounds activities from 10−3 to 10−1 c/g can be obtained without excessive radiation damage. Activities in this range have been obtained, for example, in hydrocarbons, carbohydrates, sterols, and peptides. Results of some degradative studies indicate that compounds labeled by this technique may contain tritium at all possible positions, but at a nonuniform distribution.

Our interest in the Wilzbach direct tritium-labeling procedure [1] was aroused by the possibilities it offered to obtain radioactive counterparts of sugars and sugar analogs for which chemical synthesis from C14-labeled precursors is either very difficult, prohibitively expensive, or both. With few exceptions, it seems, only naturally occurring hexoses are easily labeled with C14, inasmuch as biosynthetic methods may be used. In our older studies with animal tissue hexokinase [2], and in our more recent studies of various aspects of membrane transport of sugars in ascites tumor cells [3], kidney cortex slices [4] and intestinal epithelial cells [5, 6] we have found particularly useful a group of compounds which are analogs of D-glucose but which, unlike glucose, cannot be metabolized by animal tissues. It is this very property, metabolic inertness, so useful to us on the one hand, that is, on the other hand, an effective barrier to easy C14-labeling of these compounds.

Publisher Summary This chapter discusses the preparation of tritiated sugars. There are several methods that can be used to specifically introduce a tritium label into sugars, namely, reduction of a suitable group by a metal hydride—preferably sodium borohydride—chemical or enzymic reactions in which a hydrogen is rendered exchangeable with water, hydroboration of or addition of water to a double bond, and Wilzbach exchange with tritium gas. Most of these methods lead to a mixture of products although often one isomer predominates. As tritium is a radioactive isotope, all preparations should be conducted in an efficient hood and care must be taken when handling high activities, especially to avoid contaminating other experiments. Unstoppered water solutions rapidly exchange with atmospheric water. Exchangeable hydrogens—those attached to oxygen or nitrogen—are usually lost during evaporation of solvent or during paper chromatography.

A series of experiments on exposure of man and rats to tritium gas (HT) or tritiated water (HTO) are reported. In one human experiment 3 millicuries of HTO was administered in 200 milliliters of water by ingestion. Absorption into the blood stream was linear with time and complete in about 45 minutes. Body water turnover was measured over a period of six days by weighing all food and fluid intake and all excretory output. For four days water turnover was kept near normal (2.7 liters per day). During the last two days water turnover was increased to 12.8 liters per day. Tritium excretion rates was determined on eight other human subjects in which water turnover in which measured less precisely. The biological half-life of HTO in nine human subjects varied from 9 to 14 days on ad libitum and was reduced to 2 1/2 days in one subject on high water intake. The tritium activity in sweat, expired water vapor, septum and urine was found to be essentially the same as that in water from the blood. Rats were continually exposed to various concentrations of tritium in inspired air (0.000001 to 0.03 microcuries per ml) for periods up to 145 hours. Inhaled tritium appeared in the animal as HTO apparently being converted thus in the body.

A series of tritium-labeled sulfonylurea hypoglycemic agents was prepared by the tritium-gas exposure met hod. Sodium salts of the sulfonylureas were found to incorporate stably bound tritium more effectively than did the corresponding free compounds. Exposure to tritium gas in the presence of an electrical discharge was also found to be an effective met hod for preparing tritium-labeled sulfonylureas.

ALTHOUGH much of the progress in thyroid hormone biochemistry is due to the use of thyroxine and 3 : 5 : 3′-triiodothyronine labelled with iodine-131, the high metabolic lability of the iodine atoms makes it impossible to follow the fate of these substances beyond the stage of enzymic deiodination1. The low specific activity of thyroxine labelled with carbon-142 has ruled out its use under physiological conditions. Hence, with the availability of pure tritium gas and methods for its measurement, it was decided to prepare tritium-labelled thyroxine. The commonly used methods of exchange could not be used because of the danger of reductive deiodination by tritium gas. The procedure summarized below, and which involved the synthesis of N-acetyl-tyrosine and N-acetyl-3 : 5-diiodotyrosine as intermediates, was finally adopted. All compounds were hence labelled in 2 carbon atoms of their alanine side-chain.

The incorporation of tritium into saturated and aromatic organic compounds by the Wilzbach gas exposure method has been explained on the basis of reactions between ionized or excited organic molecules and tritium [1]. In the presently reported work, substitution† occurred in saturated fatty acid esters, but addition† was the principal reaction in higher unsaturated fatty acid esters [2]. These results suggested that varying amounts of addition and substitution of tritium might take place with different types of olefinic systems. Thus, a number of compounds representative of the more common structural types, such as methyl oleate, methyl linolenate, methyl sorbate, methyl stearolate, cyclohexene, isobutylene, cholesterol, and vitamin A acetate, were irradiated with tritium gas. The tritium incorporated either by substitution and addition or by addition only is largely determined by the substituents attached to the carbon-carbon double bond or bonds [3].

Tritiated water can be standardized by internal gas proportional counting following its chemical reduction, by means of a tritium gas generator, to produce tritiated hydrogen. In this paper a new tritium gas generator is described in detail together with the method of measurement based on the internal gas counting. It has new and improved features and offers the advantage of being simpler and easier to operate than other tritium generators available. Thus, this tritium generator has the following new features: (i) it performs the water reduction at a lower temperature (450 deg. C) than the other generators which need 600 deg. C ; (ii) the reduction yield is always unitary. Also, it has a simple and compact construction by using the same components for water degassing and water reduction. Its simple disassembly and reassembly allow for easy maintenance.

The superconductivity and reverse isotope effect have been measured in high pressure tritium gas loaded palladium tritide (PdTx) for x values from 0.72 to 0.81.

Two major injections of tritium gas into the atmosphere occurred in late 1973. They appeared to originate from underground nuclear detonations, and were detected by our sampling stations at Fairbanks, Alaska; at Miami, Florida; and at Mauna Loa Observatory, Hawaii. Total injected amount is estimated at 80 g of tritium.

A safer, more convenient and more informative pressure monitoring system for tritium gas targets is described.

Radioactive gibberellin A20 (GA20, I) was prepared by hydrogenation of GA5 methyl ester-16,17-epoxide with tritium gas followed by removal of epoxide oxygen and hydrolysis. Radioactive GA5(V) was obtained by hydrogenation of GA3 methyl ester monomesylate with tritium gas followed by hydrolysis and radioactive GA8 (XV) was obtained by oxidation of radioactive GA5 with osmium tetroxide.

Blistering of gold and platinum beam stops used in cells to contain tritium gas for neutron production targets has been observed. Such blistering becomes apparent after heavy bombardment by proton or deuteron beams of 2–10 MeV. Left unchecked, the blisters grow and eventually rupture, weakening the beam stop and possibly allowing leakage of tritium.

Proterctive coatings for stainless steel containers for deuterium/tritium gas mixtures (gas mass spectrometer calibration standards) have been evaluated by auger electron spectroscopy. An iron/oxygen rich coated surface minized isotopic exchange. (AIP).

The principle of using small amounts of high activity water in an otherwise water-sensitive catalytic system has previously been employed with Lewis acid labeling catalysts. The advantages of such procedures include the relative simplicity of handling tritiated water and its low cost compared with alternatives such as tritium gas and tritiated benzene. No vacuum techniques are necessary, and the activity of the product is limited only by the specific activity of the small aliquot of HTO used as isotope source. The reactants, organic (0.1 g), zeolite (25 mg), and tritiated water (5 ..mu..L, 40 mCi/mL) were sealed in a glass ampule and heated to 175/sup 0/C for the desired reaction time. Products were analyzed by radiogas chromatography and /sup 3/H NMR spectroscopy. The results show that the procedure represents a highly efficient method of tritiation of most aromatic compounds. Since the molar ratio of organic compound to water was high, equilibrium represents virtually 100% incorporation of the tritium utilized in the experiment.

The gas‐handling system of a simple, inexpensive gas chromatograph is described suitable for the safe and fast purity analysis of tritium gas.

WHEN tritium is introduced into (−)-inositol (I) by the Wilzbach method1—exposure to tritium gas for a prolonged period—considerable inversion occurs and tritium-labelled myoinositol (II) is one of the products2,3. It has been assumed3 that the myoinositol must be specifically labelled on C1 only since inversion occurs during the replacement of hydrogen by tritium. This assumption has now been shown, by degradation of the myoinositol, to be correct.

Halothane was labeled with tritium (Wilzbach method) by exposure to 2.3 curies of tritium gas for fourteen days. The one hydrogen of the molecule was labeled and on purification gave a final specific activity of 2.9 mc. per Gm. In the preparation a considerable amount of ‘loose’ tritium and highly active impurities were separated and the purity of the final product following gas chromatographic purification was better than 99.95 per cent.

The use of finely divided polystyrene fluff as the reaction medium for studies of reactions induced by the BETA radiation of tritium gas is reported. The electron spin resonance spectrum in the tritium--polystyrene flufff system was essentially identical with that observed in gamma-irradiated polystyrene. The degree of tritium labeling in uncrossllnked polystyrene was determined by dissolving the reacted fluff in benzene and then subjecting the benzene solutions to liquid scintillation counting. (M.C.G.)

MORPHINE has been labelled with carbon-14 in the N-methyl position by chemical synthesis1,2 and randomly by biosynthesis3,4. Because of the metabolic lability of the N-methyl group and the need for considerable quantities of a product of high specific activity, studies on the preparation of tritium-nuclear labelled morphine were initiated. The Wilzbach procedure5 of exposure to tritium gas was utilized for the introduction of the tracer element into the morphine molecule. The preparation of biologically stable tritium-labelled morphine by this technique had been described previously6, and the radiochemical purity of the product was reported. We have found, however, that the exposure to tritium gas of morphine base or morphine sulphate in finely divided form, and subsequent purification to remove the labile tritium and radio-decomposition products, uniformly gave a seemingly pure crystalline morphine which showed two distinct areas of radioactivity when paper chromatograms were developed using correctly buffered paper and the proper solvent mixtures. One area contained a greater proportion of radioactivity (approximately 65–70 per cent of total) but negligible mass of material (not detectable by spray reagents or by visualization with ultra-violet light, less than 1 per cent). Similarly when normorphine base or its hydrochloride was tritiated in the same manner and purified, the morphine synthesized from it by the method of Andersen and Woods1 showed the same trace radio contaminant. When paper chromatograms were prepared from the above tritium-labelled ‘morphine’ using non-buffered paper and several solvent mixtures, that is, n-butanol, formic acid, and water (12 : 1 : 7 v/v); 2.3 per cent p-toluene sulphonic acid in n-butanol and water (100: 14-v/v), etc., all the radioactivity was located in one area. This area was the alkaloidal spot as localized by spraying with iodoplatinate alkaloidal reagent or by visualization of the shadow with ultra-violet light. The R F values were identical with parallel non-labelled morphine.

Meprobamate has been labeled with tritium by exposure to tritium gas. Its radiochemical purity has been convincingly demonstrated, and the distribution of tritium within the molecule has been determined. The specific activity of 300 mc. per Gm. is the highest thus far reorted for a product labeled by this technique.

A simple technique is described for labeling organic compounds by mercury-photosensitized reaction with H/sup 3/ gas. In the method, a silica ampoule containing the organic sample and tritium gas, with a small amount of mercury, is irradiated at room temperature with a low-pressure mercury lamp. By this method, 10 mc of T/sub 2/ produced an activity in toluene that would have required 500 mc by other methods. (D.E.B.)

ALTHOUGH the fate of the secondary electron in the radiolysis of water has been discussed for many years, most workers have assumed that it returns to the parent ion in condensed saturated hydrocarbon systems and have interpreted radiolysis data in terms of excited molecules and free radicals. However, the occurrence of ion-molecule reactions in such systems has been discussed by Libby1 and Williams2, both of whom have put forward indirect evidence for such reactions3–6. The action of several solutes has been interpreted in terms of secondary electron scavenging7–9, and Freeman10 and Allen11 have shown by conductivity measurements on irradiated cyclohexane and n-hexane respectively that low yields of free electrons and hence positive ions occur. However, direct evidence for ion-molecule reactions in such systems is still lacking.

LABELLING of organic molecules with tritium by the Wilzbach method1 — exposure to tritium gas for a prolonged period—has become widely used, particularly for biochemical investigations. A considerable amount of decomposition always accompanies the formation of labelled material which, therefore, has to be very carefully purified. It is important to know whether replacement of hydrogen atoms on asymmetric carbon atoms may occur with inversion of configuration: if it does, diastereomers of the original compound will be formed, which may not be readily separated by recrystallization or other methods of purification. Absence of diastereomers has been reported in one case, that of 1,2,3,5-tetra-O-acetyl-D-ribofuranose2, whereas 30 per cent racemization occurred on labelling of (—)-mandelic acid3.

The 12,13- and 9,10-double bonds of methyl linoleate were found to add tritium in a ratio of 1.4 to 1, respectively. The acetylenic fatty acid ester, methyl stearolate, on exposure to tritium and on subsequent analysis was shown to yield cis- and trans-9,10-tritiooctadecenoate as the major radiochemical product and to give minor amounts of radioactive methyl stearate (saturation) and stearolate (substitution). Radioactivity observed in the C/sub 9/ dibasic and C/ sub 9/ monobasic acids resulted from substitutlon by tritium for the carbon- bonded hydrogen at carbon atoms other than numbers 9 and 10. Radioactivity in the C/sub 9/ mono- and dibasic acids corresponded to the 3 to 4% tritiated methyl stearolate isolated by liquid-liquid chromatography and gas-liquid chromatography before oxidation; radioactive stearic acid corresponded to the 9% tritiated stearic acid similarly isolated by chromatography of the uncleaved fatty acid esters. The octadecatrienoate ester, methyl linolenate, on tritium exposure and oxidative cleavage yielded some radioactive mono- and dibasic acids. Unexpectedly, a comparatively iarge amount of activity (20.3%) was associated with the linolenate peak, indicative of considerable reactlon by substitution. (TCO)

Irradiation of high-density polyethylene by ~1 atm overpressure of T2 gas at 23+- 2 degrees C has been shown to produce severe damage, about 200 MRad dose, within 6 months. Production rate of H2 gas from irradiation due to polymer incorporation of tritium increased quickly within the first 2 months, after which it slowed considerably. It is proposed that outgassing of H2 acted to inhibit diffusion of solubilized HT or T2 into the bulk, thereby limiting increases in polymer T incorporation and thus damage rate. Damage to the HDPE sample was found to be nonuniform. Laser fluorescence from the sample surface irradiated by the supply of T2 gas was ~10{sup}3-fold greater in the energy deposition layer than the fluroescence from bulk polymer after 2 months. This factor was within an order of magnitude of calculated dosages to surface and bulk. Fluorescence from the bulk, apparently caused by unsaturated polyene groups formed during irradiation, grew in time about proportionally to H2 generation and thus dose. An appreciable concentration of radical or ion-radical polyenes at room temperature could be recombined by bleaching for 15 minutes at ~150 degrees C; these species appeared to reform over night at room temperature.

Platinum and palladium containing Y-zeolite, mordenite and ZSM-5 catalyse efficient exchange at 100°C between elemental tritium and aromatic or aliphatic hydrocarbons, the tritium orientation in the organic molecule showing characteristics of both metal and zeolite catalysis. The hydrogen forms of the same zeolites (i.e. without metal) also activate elemental tritium for aromatic exchange at 120-150�C, which shows that a metal component is not necessary for activation of elemental hydrogen even at modest temperatures.

A microwave discharge system based on work described by Hembree and co-workers was constructed to produce atomic tritium for radiolabeling a variety of organic compounds of biological interest. Thi...

Specimens of L-[2,3-3H2]phenylalanine and L-[2,3-3H2]tyrosine, prepared via reduction of acylaminocinnamic derivatives with tritium gas, have been degraded to establish the tritium labelling patterns. Both amino-acids were found to be labelled approximately equally at C-2 and -3 with the tritium at C-3 in predominantly the pro-S position. Catalytic hydrogenation of (Z)-(α-acetamido[β-2H]cinnamyl)-L-glutamic acid was used to demonstrate, by n.m.r. spectroscopy, the stereochemical course of the tritiation.

In situ measurement of tritium release during irradiation provides a more realistic understanding of the tritium release mechanism than that obtained by the post-irradiation annealing method. The tritium release curves reached saturated values after irradiation of a few days at the reactor operation of 10 MW. The saturated values were in good agreement with the predicted values of the tritium generation rate obtained from neutronics calculation. Temperature dependence of tritium release under the temperature of 550°C at the pellet center was interpreted by the decomposition of LiOH(T) at the pellet surface. The ratio of tritium gas and tritiated water (HT/HTO) was strongly affected by the moisture generated from the piping system and the pellet. The retained tritium in Li2O was 0.5–0.9 wppm after the final stage of the irradiation of 760°C and the burnup of 0.24% of total Li.

Microporous aluminophosphate (ALPO) catalysts are shown to have high activity and unique specificity for exchange between elemental tritium gas and both aromatic and branched aliphatic compounds, suggesting their applicability as catalysts in a range of other reactions.

The permeability of four protective coatings to tritium gas and tritiated water was investigated. The coatings, including two epoxies, one vinyl and one urethane, were selected for their suitability in CANDU plant service in Ontario Hydro. Sorption rates of tritium gas into the coatings were considerably larger than for tritiated water, by as much as three to four orders of magnitude. However, as a result of the very large solubility of tritiated water in the coatings, the overall permeability to tritium gas and tritiated water is comparable. Marked differences were also evident among the four coatings, the vinyl exhibiting an abnormally high retention of free water because of a highly porous surface structure. It appears that epoxy coatings having a high pigment-to-binder ratio are most suited for coating concrete in tritium handling facilities.

A technique was developed for direct field sampling of atmospheric HTO and HT. Airborne, portable, and laboratory versions were implemented, and a comprehensive sampling program begun. The air is passed first through Molecular Sieve to adsorb the water, then over palladium carried on Molecular Sieve, which oxidizes atmospheric hydrogen and adsorbs the resulting water in situ . Both samples are subsequently extracted from the adsorbers, and the tritium content measured by internal low-level gas counting. Resolution is 4% of present atmospheric levels. Monitoring of HT and HTO at three stations in the Northern Hemisphere shows that HT does not undergo seasonal fluctuations like HTO, and variations are small around the present mean of about 46 HT molecules per mg air. After the previous rise from pre-nuclear level, the tropospheric HT-inventory has reached a steady state within the past few years. Sampling transects from 40°N to 65°S in 1971 and 1972 show similar HT levels in the Northern and Southern Hemispheres indicating a long residence time of HT (and hydrogen). The HT appears to have its source at ground level, most likely from nuclear fuel element processing, underground nuclear fusion device detonations, and military and civilian handling of tritium gas. In the troposphere, there is now more tritium as gas (HT or T 2 ) than as HTO (water vapor). DOI: 10.1111/j.2153-3490.1974.tb01955.x

The spectrum of light in the range 350–800 nm emitted by pure tritium gas (T2) in a closed optical cell with no external excitation has been recorded photographically and by single-photon counting. Prominent in the spectrum are the Balmer series of atomic tritium, lines of 3He that grow with time, and the T2 ultraviolet continuum.

Sphingomyelin, galactosylceremide, glucosylceremide and GM 2 (or Tay-Sachs) ganglioside were isolated and purified. The lipids were then dissolved in methanol and hydrogenated with tritium gas in the presence of platinum oxide catalyst. After hydrogenation and removal of excess tritium the lipids were re-purified by preparative thin-layer chromatography, or by column chromatography. The radiochemical and chemical purities of the various compounds were evaluated by thin-layer and gas-liquid chromatography of products formed after hydrolysis in 0.75 M methanolic hydrogen chloride. All lipids incorporated tritium almost exclusively into the hydrophobic part of the molecule. The ratio of the specific activities of fatty acid to long-chain base in the various sphingolipids was of the order of 4, thus indicating that the bulk of the radioactivity had been incorporated into the fatty acid moieties. Initial experiments with two of the radioactive lipids prepared in this manner, sphingomyelin and galactosyl-ceramide, have confirmed their value in the diagnosis of Niemann-Pick and Krabbe's diseases respectively.

Analysis by tritium n.m.r, of triethylsilane, tetramethylsilane, hexamethyldisiloxane and chlorodimethylsilane exchanged with tritium gas over Raney nickel at 100°C shows that exchange readily occurs in alkyl substituents as well as with silyl hydrogen; novel species involving charge-transfer intermediates in dissociative adsorption at the C-H as well as the Si-H bonds are proposed to explain the data.

The construction and calibration of a simple ionization-chamber apparatus for measurement of high level tritium gas is described. The apparatus uses an easily constructed but rugged chamber containing the unknown gas and an inexpensive digital multimeter for measuring the ion current. The equipment after calibration is suitable for measuring 0.01 to 100% tritium gas in hydrogen-helium mixes with an accuracy of a few percent. At both the high and low limits of measurements deviations from the predicted theoretical current are observed. These are briefly discussed.

A ceramic electrolysis cell and a palladium diffuser have been developed in Japan and tested with tritium at the Tritium Systems Test Assembly (TSTA) at the Los Alamos National Laboratory, to test their feasibility as possible upgrades for the fuel cleanup system (FCU). The ceramic electrolysis cell, made of stabilized zirconia, was operated at 630/sup 0/C for an extended period with a mixture of 3% T/sub 2/O in He carrier gas in a circulation system with an oxidizing catalyst bed. The palladium diffuser was tested with pure tritium gas, circulated at 280/sup 0/C, to verify the compatibility of the alloy with tritium, since the /sup 3/He produced in the metal could cause degradation. The isotopic effects were also measured for both devices.

In the course of studies on the hazard of exposure to tritium gas and tritium oxide-contaminated atmospheres, data were obtained on the passage of these substances through the skin. Results on the percutaneous absorption of water and tritium oxide have been previously reported (1, 2). This paper reports results obtained on excised pieces of skin exposed to tritium gas and the application of these results to radiation hazard control. Previous reports of the permeability of skin to hydrogen gas are apparently limited to a study employing a membrane simulating human epidermis (3).

WILZBACH1 has recently described a convenient method for labelling organic compounds involving their exposure to tritium gas; but both he and others2,3 found that appreciable amounts of the exchanged radioactivity appeared in traces of highly tritiated contaminants as well as in labile positions. We have applied this method to the labelling of 1 : 6-dihydroxyhexœstrol, an œstrogen analogue4, and similarly have found that impurities contain the major part of the incorporated non-labile tritium.

The radiation-induced colour in silica gel is bleached when tritium gas is admitted and this bleaching process activates the tritium in such a way that when a hydrocarbon is later admitted it becomes labelled. Best yields (up to 130 mCi g–1) are obtained for aliphatic hydrocarbons having a methyl group attached to a tertiary carbon atom, often with a high degree of radiochemical purity. The number of tritium atoms incorporated appears to be comparable with the number of F centres in the irradiated silica gel.