Liquid or Vapour Phase: Specifying Storage Temperature in the Embryology LaboratoryCryolabCryolab Ltd25 September 2026 |
Storage temperature is quoted as one number and it is not one. Samples immersed in liquid nitrogen sit at minus 195.8 degrees Celsius, uniformly, because the boiling liquid holds the whole canister at its boiling point. Minus 196 is the rounded figure most documentation uses.
Vapour phase storage is not at that temperature. Samples sit above the liquid in cold nitrogen gas, which removes direct contact with the liquid and the cross contamination route that comes with it. The ASRM and SART Practice Committees, writing on cryostorage in Fertility and Sterility (2020;114:486-491), note that liquid nitrogen is not sterile, which is the foundation of the vapour phase argument.
The trade off is a vertical temperature gradient. The bottom of the canister sits close to liquid temperature and the top sits warmer, by an amount that depends on vessel design, liquid level and how often the lid is opened. For an embryology laboratory the practical consequence is that the temperature to specify against is the warmest position a straw or vial can occupy, not the temperature at the bottom of the vessel. An inventory that fills the top of a canister in a vessel running at a low level is the specific failure this produces, and it produces it without any visible sign.
That is also why level monitoring carries more weight in vapour phase. In liquid phase a falling level still leaves the depth of liquid covering the samples as a margin. In vapour phase the samples are already above the liquid, so every centimetre lost pushes the warm end of the gradient further down the canister. The ESHRE recommendations on good practice in the IVF laboratory, published in Human Reproduction 41(8), 1245, expect cryostorage tanks to be continuously monitored with alarms that detect and log out of range temperature or liquid nitrogen level. A daily manual dipstick check is a point observation of a variable that moves between observations.
Decide liquid or vapour phase deliberately and document the reason, since it is among the first things an inspector asks. Specify monitoring to match, with a remote output and a relay to a system somebody answers out of hours. And track nitrogen consumption from day one, because a rising trend at unchanged workload is the earliest indication that the vessel's vacuum is degrading.
Full article: https://cryolab.co.uk/liquid-nitrogen-storage-temperature/
https://cryolab.co.uk/liquid-nitrogen-storage-temperature/
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