67Ga: a novel internal standard for LSC

The liquid scintillation spectrum of 67Ga exhibits two monoenergetic peaks that correspond to the average energies of 3H and 14C. This interesting feature prompted experiments designed to use 67Ga as an internal standard for either 3H or 14C or dual-labelled samples. A parameter based upon the ratio of the measured activity of the two 67Ga peaks was chosen to reflect the degree of sample quenching. As an example, a dual-labelled experiment was performed and the equations relating the counting efficiency to the 67Ga ratio are presented. The main advantages of this technique include the ability to recover the sample after the 67Ga has decayed, and the elimination of accurate pipetting of the internal standards as only the ratio of activity between the two peaks need to be considered