On the use of liquid scintillation counting ofCr andC in the twin tracer method of measuring assimilation efficiency.

Calow and Fletcher (1972) calculated assimilation efficiency from the ratio of an assimilated radiotracer (C) to a non-assimilated tracer (Cr) in food and feces. Wightman (1975) improved the efficiency of their technique by using liquid scintillation to count both isotopes simultaneously, but stated incorrectly that it was not necessary to convert counts per minute (CPM) to disintegrations per minute (DPM). Unless the CPM data are corrected for quenching and converted to DPM prior to calculation of assimilation efficiency, a significant error may be introduced.