Radiochemical and Chemical Stability

Tritium has83 a half-life of 12.26 years, and so radioactive decay of the label can usually be neglected. However, the radiation emitted 

Most tritiated sugars are best stored in aqueous solution, sometimes containing a small proportion of ethanol. Under these conditions, radiolysis usually does not exceed 5 to 10% per year. In the frozen state, between 0° and —196°, the rate of decomposition can be high, presumably due to concentration of the sugar in pockets on freezing.87 Nucleotides are stored at —20° in 50% ethanol, which acts as a free-radical scavenger,68 and decompose at the rate of 12% per year polymers should be stored as freeze-dried solids. 

Exact localization of the hydrogen isotope is usually required, and it is inadvisable to rely on the method of synthesis, as the label is not always situated entirely at the position predicted.69 In many mechanistic and biological studies with enzymes, the position of the label alters during the reaction, and, in others, where a proton isotope from the solvent is incorporated, it is important to localize the incorporated isotope, and, if it is at a methylene group, to determine its stereochemistry. 

Alternatively, a procedure that specifically removes the tritium by ionization, or oxidation to water-t, can be used. Thus, the presence of isotopic hydrogen at C-l of aldoses was confirmed by oxidation, either by re-isolation of the aldonic acid,7 or by measurement of the isotope appearing in the water.26 Other oxidative procedures have involved oxidation to D-glucaric acid,75 the platinum-catalyzed oxidation19 of mt/o-inositol-2-f, bacterial oxidation75 of D-glucitol-5-t, and osazone formation.76 

Whenever possible, it is important to test the degradation methods by using authentically labeled molecules, because, sometimes, unforeseen exchanges occur. Thus, it has been reported that only 

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