A superior counting solution for water-soluble tritiated compounds.

We describe a simple liquid-scintillation solution for use with water-soluble tritiated compounds that is superior to other such systems. Its advantages include: (1) a refrigerated-type liquid scintillation spectrometer is not needed because the solution has extremely good thermal stability from 22#{176} to 75#{176}C; (2) counting efficiencies are high from pH 1-12, therefore eliminating neutralization; (3) a sample is stable for at least one week, with a 7% variation in counting after three weeks (a comparison with counting in Bray’s and Triton X-100 solutions is included); (4) there is no detectable phosphorescence or chemiluminescence; (5) toluene need not be analytical grade; (6) for more than 10,000samples, efficiency has deviated less than 5%; (7) there is no odor (except forthetoluene) as with naphthalene “cocktails” (Bray’s solution); (8) cost of the system compares favorably with that for other counting systems; (9) plastic vials can be used (40% less costly than glass) and are easily cleaned because of the detergent qualities of the cocktail. The only obvious disadvantage of the system is that high salt concentrations (>5 g of NaCI per 100 ml) cause a marked decrease in efticiency of aqueous radioactivity, and somewhat erratic counting for the toluene internal standard. However, additional solubilizer will sometimes correct this problem.