Determination of the Liquid Scintillation Counting Efficiency of 3H and/or 14C Labelled Samples Independently of the Degree of Colour and/or Chemical Quenching

Abstract

Abstract A value R is obtained by the ratio of the summed, coincident pulses of both photomultipliers to the coincident pulses of one photomultiplier in the same selected range of the external standard puls height spectrum. This value R together with the external standard channel ratio (ESCR) show the extent of chemical and/or colour quenching in a field described by a set of calibration samples with increasing chemical or colour quenching (Fig. 3). The counting efficiency of samples with different and unknown proportion of chemical and/or colour quenching can be determined much more accurate than by any calibration approach using the ESCR only (Table VI). The method can be used for 3H samples with a counting efficiency ≧10% and 14C samples of ≧5%, respectively. The new correction procedure is also applicable for 3H and 14C double-labelled compounds.