Liquid scintillation counting of (3H) and (14C) on solid supports: a warning.

Liquid scintillation counting of (3H) and (‘“C) -labeled compounds on solid supports is a common practice in biochemistry. Furlong has recently emphasized “local quenching” of tritium by filter paper, and has suggested that p’s of higher energy might also be anomalously absorbed if they penetrated under the surface of a filter paper support (1, 2). It is the purpose of this report to show that such local “selfabsorption” occurs when (%)-labeled small molecules are counted on various solid supports. The losses of (‘“C) efficiency, although not as profound as those of (3H), are very significant when (‘“C) discrimination settings for double-isotope counting are used.