RECENT ADVANCES IN SAMPLE PREPARATION

Although new concepts in the preparation of samples for liquid scintillation counting have not emerged, some im-provements have been made. We now have, for example, a range of solubilizing agents which are more effective and less quenching than Hyamine-hydroxide and we can count several milliliters of aqueous material where, previously, we were restricted to a few microliters. In the area of combustion techniques we have traveled a route which start-ed from tedium with a touch of hazard and is now firmly headed for automated convenience. What has also changed is the application of liquid scintillation counting to samples generated by current analytical techniques such as gel electrophoresis and radioimmunoassay. Certainly a new dimension to radioisotopic techniques has been added by the recognition that energetic beta-emitters such as can be counted directly in a liquid scintillation counter by Cerenkov radiation. A sample for liquid scintillation counting consists of 4 components: 1) the solvent 2) scintillator 3) sample 4) the sample container or counting vial. Solvents Toluene remains the best general purpose solvent with regard to energy transfer efficiency, solubility of the scintillator, availability, uniformity and cost. The para and meta xylenes are more efficient solvents than toluene giving a 10 % increase in pulse height. Since the various xylenes have different energy transfer efficiencies ensuring the uniformity of solvent composition adds to the cost of this system although xylene is used as the major solvent in some commercial preparations of ready-to-use cocktails. The solvent is one of the least efficient components of the counting system since 90 to 95 percen