This phrase begs the question: “Well then, what sort of cryogenic vial is this if it cannot be used in liquid nitrogen?”
Not a week goes by that we are not asked to explain this seemingly odd disclaimer which appears on every cryovial product page regardless of the manufacturer, regardless of volume and regardless if its an internal thread cryovial or external thread cryovial.
The answer is: This is a matter of liability and not a question about the quality of the cryovial.
Like most durable laboratory tubes, cryovials are made from temperature stable polypropylene.
The thickness of the polypropylene determines the safe temperature range.
Most 15mL and 50mL conical tubes have thin walls which limits their functional use to temperatures no lower than -86 to -90 Celsius.
Thin walls also explain why 15mL and 50mL conical tubes are not advised for spinning at rates faster than 15,000xg as the plastic is prone to split and crack if operated beyond this threshold.
Cryogenic vials are made from a thicker polypropylene which allows them to hold up under much colder temperatures and be spun in a centrifuge at speeds in excess of 25,000xg or more.
The trouble lies with the sealing cap used to secure the cryovial.
For a cryovial to properly protect the tissue, cell or virus sample it contains, the cap must screw down completely and form a leakproof seal.
The slightest gap will allow for evaporation and risk contamination.
Painstaking efforts are made by cryovial manufacturers to produce a high-quality seal which may include a silicon o-ring and/or thick threading for screwing the cap down fully.
This is the extent of what a cryovial manufacturer can deliver.
Ultimately the success or failure of the cryovial to preserve a sample fall on the lab technician to ensure a good seal has been made.
If the seal is poor, and even in cases where the cap has been properly closed, liquid nitrogen can seep into the cryovial when it is submerged in liquid phase liquid nitrogen.
If the sample is thawed too quickly, the liquid nitrogen will rapidly expand and cause the pressurized contents to explode and send plastic shards into the hands and face of anyone unfortunate enough to be nearby.
Therefore, with rare exceptions, cryovial manufacturers require their distributors to boldly display the disclaimer not to use their cryovials except for the gas phase of liquid nitrogen (around -180 to -186C).
You can still quickly flash freeze contents in a cryovial by partially submerging it in liquid phase nitrogen; they are durable enough and will not crack.
Want to learn more about the hazards of storing cryogenic vials in liquid phase liquid nitrogen?
Here is an article from UCLA’s Center for Laboratory Safety documenting an injury due to an exploding cryovial.
Post time: Apr-21-2022