edned by
GALEN W. EWlNG Saton Hall University South Orange. New Jeney 07079
XCI. Combustion Instruments for Preparing Samples for Liquid Scintillation Counting John I. Peterson Biomedical Engineering and Instrumentation Branch, Division of Research Services, National Institutes of Health, Public Health Service, Bethesda, Maryland
Liquid scintillation counting has become an important and universally used method for the quantitative measurement of radioactively tagged organic and biological molecules used as tracers. Tritium (hydrogen-3) and earbon-14 are ideal isotopes for this because they can be incorporated into many molecular structures, are relatively safe to use, and generally cause little or no molecular disruption; they are weak beta emitters with convenientlv. lone- half lives (12.3 years for tritium and 5730 years for carbon14). The law energy of the emitted beta particles (0.049 MeV average, 0.158 MeV maximum for earbon-14 and 0.005 MeV average. 0.018 MeV maximum for tritium) ( I ) dictates the use of the liquid scintillation counting technique for measurement. This has com~ l e t e l y supplanted the Geiger counting methodology common 25 years ago because of the latter's impracticality for measuring articles which are strongly absorhed by the sample itself, the intervening air, and the window of the counter. Ideally, in liquid scintillation counting, the sample is in complete solution in a solvent, rommonlv called a cocktail. which has been d r r t p r d to dl, several things. The primary funrti
