Tritium tracer applications

The examples presented in Sections IA-ID clearly demonstrate the general utility of sulphonic acid derivatives in the syntheses of isotopically labelled compounds. Sulphonate esters possessing the excellent anionic leaving sulphonate group are especially useful. Numerous labelled sulphonic acid derivatives have been directly applied to solve scientific, industrial and medical problems. The kinetic deuterium and tritium isotope effects, which limit to a certain degree the tracer applications of deuterium- and tritium-labelled sulphonic acid derivatives, are discussed in Section III. 

Plants capable to produce a total of more than 1200 tons annually are in operation in Canada, India and the US. The largest exchange towers are 60 m high and have a diameter of 6 m. In 5 units (only one unit is indicated in Fig. 2.8) the D2O concentration is raised from 0.014% to about 15%. The final concentration to 99.97% D2O is then usually made by distillation of water. The 1990 price for pure D2O was - US 400 per kg. It is important to recognize in tracer applications that commercially available D2O always contains some tritium, which is co-enriched with deuterium 2-7 kBq kg D2O. 

Decay products of the principal radionuclides used in tracer technology (see Table 1) are not themselves radioactive. Therefore, the primary decomposition events of isotopes in molecules labeled with only one radionuclide / molecule result in unlabeled impurities at a rate proportional to the half-life of the isotope. Eor and H, impurities arising from the decay process are in relatively small amounts. Eor the shorter half-life isotopes the relative amounts of these impurities caused by primary decomposition are larger, but usually not problematic because they are not radioactive and do not interfere with the application of the tracer compounds. Eor multilabeled tritiated compounds the rate of accumulation of labeled impurities owing to tritium decay can be significant. This increases with the number of radioactive atoms per molecule. 

By far the most important application of tritium is its use as a radioactive tracer in extensive labeling studies. The production of tritium-labeled organic compounds was greatly enhanced with the discovery that tritium could be introduced to a compound merely by storing that compound under tritium gas for a few days or weeks the radiation induces exchange... 

With the development of liquid scintillation counters which permit tracer levels of tritium to be measured accurately, isotope exchange reactions are now usually carried out with tritium rather than deuterium. Frequently, however, it is useful to compare rates of exchange for all three isotopes and deuterium exchange may be followed using, for example, mass spectrometry [22]. An example of the application of isotope exchange to proton transfer from carbon is shown in eqns. (8) and (9) for the hydroxide ion catalysed exchange of phenylacetylene in aqueous solution [23], viz. 

As mentioned above H- He age and isolation age unfortunately do not exactly agree in mixed waters. Nevertheless, direct application of H- He age for quantification of water exchange is possible but limited to cases where (1) the concentration is approximately homogeneous, and (2) the water age is small compared to the half-life of tritium. The second condition is required because if H- He ratios are small the water age can be linearized (Eqn. 34). If both conditions are fulfilled, mixing affects the H- He age in the same way as Hetn. Then, the H- He age behaves as a bio-geochemically inert tracer with a constant source term increasing the age by 1 yr per yr and the H- He age can be treated as an ideal tracer of the isolation age. 

Since the early 1930 s, when deuterium first became available, a tremendous amount of research on catalytic reactions has been done using heavy hydrogen as a tracer (1-4)- Space permits mention of only a few of the applications of deuterium and tritium as tracers. Perhaps the most prominent use that has been made of deuterium as a tracer is in connection with the study of the reaction (S)... 

The requirement of high specific activity restricts the choice of nuclide principally to tritium, iodine 125 and cobalt 57. A high specific activity is required because the nuclide must serve as a tracer to a trace amount of analyte. Carbon 14 and other nuclides commonly used as tracers are generally not satisfactory for RIA applications. 

Tritium ( H or T) finds wide application in tracer studies in chemistry, biochemistry, and medicine (1), as reference to Chemical Abstracts demonstrates (2). This is largely because tritium is an isotope of hydrogen and has a radioactive nucleus with a convenient half-life of 12,35 y. The decay product is He. 

As regards the relative merits of deuterium and tritium as isotopes of hydrogen (protium) for tracer and mechanistic studies, it must at once be stated that these isotopes are complementary. Each has advantages for specific applications. When molecular motion in macromolecules, lipid layers, membranes. 

The properties of tritium and carbon-14 are well suited for use as tracers in many life sciences and chemistry applications. Table 1.1 lists the important physical properties of the isotopes. 

So far, the only published use of (cod)Ir(hfpd) in tritium labeling has been a tracer experiment with a model compound, but the method should work generally with tritium gas. It remains to be seen how broad the applicability will be to complex substrates. The utility of this catalyst class appears to be largely complementary to that of the iridium phosphine class, mainly because of its apparently general ability to label benzylamines and anilines and its activity in DMF and DMA solvents. Nitro groups tend to be reduced. But as with iridium phosphine complexes, (cod)Ir(hlipd) tends to reduce double bonds but... 

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