Practical aspects of internal-sample liquid scintillation counting

Abstract

The appearance of commercially available equipment has made it practicable for chemists and biochemists to consider the use of liquid-scintillation counting for the assay of radioactive samples. The method offers excellent sensitivity for weak beta-emitting isotopes, including tritium. This is because of its 4π geometry for samples as large as several grams. The disadvantages of the technique are discussed in detail. The equipment is several times as expensive as most other counting apparatus. It is more complex to understand and to maintain. The method involves certain prerequisites of the sample material. These include adequate solubility in the rather limited group of alkyl benzene and polyther solvents that suffice as liquid-scintillation solvents, absence of color, and freedom from quenching action upon the scintillation phenomenon. Toluene remains the solvent of choice, but its usefulness has been broadened through the use of 2-ethylhexanoic acid and a quarternary ammonium base which form toluene-soluble salts with many cations and anions. The applicability of liquid-scintillation counting to any counting problems should be evaluated specifically. In general, however, some of the applications in which it appears to be the method of choice include nearly all tritium counting, assaying C 14 and S 35 samples of low specific activity, any type of counting where speed and ease of sample preparation are necessary, and the counting of volatile compounds.