Three methods for efficient detection of 3H and 14C on thin layers are described. The first method uses 0.4% PPO dissolved in 2-methylnaphthalene. It is approximately 15-fold more efficient than 7% PPO-ether for 3H detection and ISfold more efficient than autoradiography for 14C (or YS) detection. The second method uses PPO dissolved in ether. Efficiency of 3H detection increases as the PPO concentration is increased. The third method uses melted PPO and is as efficient as the first method when the film is exposed at -78Β°C.
Autoradiographic
detection of 3H on solid supports is a very inefficient process because of the low energy and range of the 3H p particles. Sensitivity can be greatly increased by impregnating the support with a scintillator such as PPO (1,2) and detecting the emitted light rays rather than /3 rays. This later process is called fluorography instead of autoradiography. Randerath (1) has made detailed studies of most of the variables involved in fluorography.
Efficient scintillation fluids usually contain a solvent in addition to the scintillator. The solvent molecules are an integral part of the scintillation process in that they collect the energy from the emitted p rays and transfer it to PPO molecules, which then emit photons (3). In extending this analogy to solid supports, we have found that incorporating a solvent into the system greatly increases the detection efficiency for 3H and 14C. The most efficient system described here (Method 1) utilizes 2-methylnaphthalene as a solvent.
We have also found that there is no optimum concentration of PPO in ether when plates are dipped, but that increasing concentrations of PPO in ether result in higher sensitivities (Method 2). The ultimate development of Method 2 is to use pure PPO. Dipping plates in melted PPO constitutes Method 3.
Methods
PPO was from Pilot Chemicals. Scintillation grade naphthalene was from Fisher. Gold label 2-methylnaphthalene was from Aldrich.