Single Phototube Liquid Scintillation Counting of C¹⁴: Application to an Easily Isolated Derivative of Blood Glucose

¹ From the Departments of Biology and Instrumentation, Brookhaven National Laboratory, Upton, New York

Conditions for efficient and reproducible liquid scintillation counting of C¹⁴ using a single phototube are described. The amplifier, scaler and power supply are the same as those used for the gas-phase proportional counting of C¹⁴O₂ admixed with P-10 gas (9:1 argon-methane). A compound which will dissolve to the extent of about 10 mg/25 ml of xylene or 4:1 xylene-ethanol, which does not absorb light in the blue region and which does not quench phosphor scintillations can be assayed for C¹⁴ by this method with a sensitivity about equivalent to that of the gas-phase counting method which entails combustion of the compound to CO₂. The counting efficiency in xylene is about 80% and in 4:1 xylene-ethanol about 70% of the C¹⁴ disintegrations occurring in the sample. The background counting rate is about 90 counts per minute. Glucose, isolated as the phenylosazone from a biological fluid, is converted to the glucosotriazole derivative. The derivative is held in solution, with the aid of H₃BO₃, in 25 ml of 4:1 xylene-ethanol containing 0.24% of the phosphor PBD (2-phenyl-5-(4 biphenylyl) 1,3,4-oxadizole). The standard deviation for individual samples in a specific activity determination, including the error in weighing the 10-mg sample of glucosotriazole derivative, is ±1.7%