How to freeze 1.5ml tubes in liquid nitrogen (caspadria trick)
Step 1: Place the tubes into a polystyrene foam rack. Make sure that the caps are tightly closed.
Step 2: Throw the rack (with care) into a liquid nitrogen canister.
Let them freeze (10-30sec).
Step 3: Using forceps, carefully remove the rack from the liquid nitrogen.
And store in a most suitable way for you (at -80C).
Advantages of freezing this way:
1) The sample never goes to the caps!
2) Tubes never capture any nitrogen and therefore never pop when thawed!
3) Tubes are kept in an organized order.
4) Since all of the sample is at the bottom of the tube, the samples thaw faster.