SOLID-PHASE REVERSIBLE TRAP FOR [C-11] CARBON-DIOXIDE USING CARBON MOLECULAR-SIEVES

A simple, maintenance-free trapping technique which concentrates and p urifies no-carrier-added (CO2)-C-11 from gas targets is described. The trap requires no liquid nitrogen cooling and has no moving parts besi des solenoid valves. It employs carbon molecular sieves to adsorb (CO2 )-C-11 selectively from gas targets at room temperature. Nitrogen, O-2 , CO, NO and moisture in the target gas which could interfere with sub sequent radiochemical steps are not retained. Trapping efficiency of 1 g of sieve for (CO2)-C-11 from a 240 cm(3) target gas dump and helium Bush cycle is >99%, and the adsorbed (CO2)-C-11 is recovered quantita tively as a small concentrated bolus from the carbon sieve trap by the rmal desorption. This durable trap has performed reliably for more tha n 1 y with a single charge of carbon sieve. It has simplified the prod uction, and improved the yields of several C-11-radiochemicals at this laboratory.