Freeze-Pump-Thaw

The freeze-pump-thaw method is an effective way of degassing solvents, solutions or liquid reagents.

Step 1: Seal the Schlenk flask and contents to be degassed 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).

FPT1
Sealing the Schlenk flask prior to freezing.

Step 2: Freeze the Schlenk flask and its contents in a dewar of liquid nitrogen. Ensure that the stopcock remains closed during freezing.

FPT2
Freezing in liquid nitrogen.

Step 3: 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.

FPT3
Evacuating the headspace under vacuum.

Step 4: 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.

FPT4
Thawing the frozen solvent/solution/reagent.

Step 5: Repeat steps 2-4 two more times for a total of three freeze-pump-thaw cycles.