APPARENT AND ACTUAL C-14 RETENTION IN THE SLOWER TURNOVER BICARBONATE POOL IN MAN WHEN USING LIQUID SCINTILLATION-COUNTING

The use of liquid scintillation counting to determine 14CO2 expiration without correct calibration of the apparatus suggests that about 25% of the label is retained within the slower turnover bicarbonate pool. Calibration reduces this figure to 13% and is in agreement with the figure obtained using a calibrated ionisatin chamber. The discrepancy is due to reduction in the specific radioactivity in the vial, the mechanism involved being unknown, but it may be a characteristics of certain liquid scintillators under certain conditions. © 1979.