The freeze-pump-thaw method is an effective way of degassing solvents, solutions or liquid reagents.
Step 1: Close the stopcock on the Schlenk flask to seal the contents under inert gas. It is essential that the Schlenk flask is not open to a flow of inert gas whilst being frozen in liquid nitrogen (see Schlenk Line Safety for more information).
Step 2 – Freeze: Freeze the Schlenk flask and its contents in a dewar of liquid nitrogen. Ensure that the stopcock remains closed during freezing.
Step 3 – Pump: Once the contents of the Schlenk flask have frozen, open the stopcock to evacuate the headspace. Keep under vacuum for 3-5 minutes whilst submerged in liquid nitrogen.
Step 4 – Thaw: Close the stopcock to seal the flask under vacuum and remove from the dewar of liquid nitrogen. As the solvent/solution/liquid thaws, the dissolved gas will escape into the headspace.
Step 5: Repeat steps 2-4 two more times for a total of three freeze-pump-thaw cycles.