Pulse height spectral analysis of 3H:14C ratios

Activity ratios of 3H:14C of isotope-labeled substances are employed commonly in biochemical studies of reaction mechanisms and pathways. The liquid scintillation pulse height spectral index (SIS) of a composite sample of 3H and 14C was demonstrated to provide an index to the 3H:14C activity ratio of the sample. Linear and logarithmic relations between the 3H:14C activity ratio and SIS were defined for a given level of quench. When the level of quench is maintained constant, the SIS was demonstrated to be directly correlated to the 3H: 14C activity ratios of the sample. A mean recovery of 102.3% was obtained for calculated 3H:14C activity ratios over the range of 0.097:1–9.698:1. The method described provides the 3H: 14C activity ratios of samples without the need for determining the separate activities of the individual radionuclides of the dual label.