Liquid scintillation counting of calcium-45 in biological material

Several scintillator solutions were tested for direct mixing with biological material for determination of calcium-45 radioactivity. For each system the capacity for aqueous solutions and stable calcium, the interference of various ions present in biological material, the stability of counting samples, and the possibility of quenching correction were determined. The results showed that the best capacity for aqueous acid solutions had Insta-Gel and Unisolve-1 scintillants. Triton-toluene-based scintillant showed marked unstability when mixed with biological fluids. The strongest quenching effect was produced by the yellow color of the ferric ion, which could be eliminated by complexing with the fluoride ion. For biological material of sufficiently high radioactivity the most convenient method seems to be counting the samples on filter paper in a toluene-based scintillator, especially since self-absorption in such a system can be corrected for by the channel and external standard ratio