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Publisher Summary This chapter discusses the loss of radioactivity and decreased fluorescence quantum yield regarding how one decides whether a quench correction algorithm is appropriate for a specific sample. For standardization to be valid, the samples must be both homogeneous and similar to the series of standards used to construct quench-correction curves. A homogeneous sample can be defined as one in which the composition of the volume traversed by emitted radiation is the same everywhere. E. B. Muller has proposed a fairly rigorous basic test of homogeneity in surfactant systems: that the efficiency of counting 3H20 and 3H-toluene be identical. A somewhat less sensitive but more generally applicable test is the double ratio plot: comparison of a quench correction curve derived using sample channels ratios to one obtained with external standard channels ratios. If the two are discordant for quenched samples the sample is not homogeneous. It is also obvious but probably important to mention that a significant portion of energetic radioactivity may escape altogether from the counting vial. In such a situation, quenching may result in an apparent increase in counting efficiency.

We have presented simple rapid procedures for calculating the absolute radioactivity of samples labeled with one or two isotopes, given the cpm from liquid scintillation counting and an external standard ratio or external count rate. Data were entered via key-board into a small off-line laboratory computer, either the Olivetti Programma 101 or the Wang 380 system. Entry was automatic when a Beckman Omega double-tape reader or a Wang tape editor was included in the respective systems. The information for calculating efficiency of counting from an external standard cpm or ratio data was derived from a linear least-square analysis or from a second-order regression analysis carried out with the computers, which were also available for general laboratory computation and statistical analysis.