A method for obtaining the true activity and counting efficiency of a T sample partially or completely adsorbed on the walls of a counting vial by liquid scintillation counting is presented.
Adsorption of a radioactive sample to the walls of a counting vial is a serious and often overlooked problem in liquid scintillation counting, particularly the counting of highly polar, biological samples (1). Although the changed counting geometry caused by adsorption gives rise to meaningless counting dat,a, there is, at the present time, no method to correct for this, and thus to obtain the true activity of such a sample. In order to circumvent t,he problem, practically the only course of action that can be followed is to dilute with inactive carrier (if available) to constant activity (1).
In this connection we wish to report that. we have developed a method that enables t'he correction of liquid scintillation counting data of adsorbed 14C-labelled compounds to yield true activities. The method introduces a second counting efficiency term, E, termed the adsorption counting efficiency, in addition to the normal counting efficiency, Eff, and is applied as shown in Eq. [l], cpm X lo4 Activity (dpm) = Eff x E 11