What temperature must liquid nitrogen be maintained at during storage, and why does it matter for biological samples?

Liquid nitrogen storage operates at -195.8°C at atmospheric pressure, which is its boiling point. In practice, LN2 within a closed dewar will remain at or very close to this temperature as long as there is liquid present and the vessel’s vacuum insulation is intact. The temperature does not drift gradually – it stays at the boiling point until the liquid is fully evaporated, at which point the vessel transitions to vapour phase only and temperatures begin to rise.

This characteristic matters enormously for biological sample management. The critical threshold for biological preservation is approximately -130°C. Below this point, the glassy state of vitrified cells means that molecular motion effectively stops and biological degradation does not occur. Above -130°C, ice crystal formation and enzymatic activity resume, compromising sample integrity.

This is why the transition from liquid to vapour phase in a dewar is a genuine risk event, not a minor inconvenience. A vessel that runs dry does not immediately warm to room temperature, but the rate at which temperatures rise through the -130°C threshold depends on the thermal mass of the vessel and the samples within it. In some circumstances, labs have successfully recovered samples from a vessel that ran briefly dry. In others, samples stored near the top of the vessel, furthest from the residual cold mass, have been compromised before the vessel was refilled.

Vapour phase storage systems maintain samples above the liquid surface, typically at temperatures between -140°C and -190°C depending on the vessel design and LN2 level. This eliminates the cross-contamination risk of liquid phase storage whilst still providing the thermal margin needed for safe long-term preservation.

The difference between -150°C and -160°C in vapour phase storage may seem negligible, but at higher temperatures within this range, the risk of ice recrystallisation during temperature fluctuations during access events increases meaningfully.

Cryolab supplies both liquid and vapour phase storage vessels for UK IVF laboratories and biobanks. View the range at cryolab.co.uk/product-category/storage-vessels/.