Liquid nitrogen dewar storage and vapour phase storage are two distinct approaches to maintaining biological samples at cryogenic temperature, and the choice between them has implications for cross-contamination risk, temperature uniformity, and consumable specification. Both approaches maintain samples below the critical -130 degrees C threshold, but the physical environment the sample experiences differs in measurable ways.

What is the temperature difference between liquid phase and vapour phase storage?

In liquid phase storage, samples are immersed in liquid nitrogen at -195.8 degrees C. Temperature is uniform and precisely defined by the boiling point of nitrogen at atmospheric pressure. In vapour phase storage, samples are suspended above the liquid surface in the nitrogen vapour. Temperature in the vapour zone varies with height above the liquid: positions closer to the liquid surface may be at -180 to -190 degrees C, whilst positions near the top of the vapour zone may be at -140 to -150 degrees C. All positions should be verified to confirm they remain below -130 degrees C.

What is the cross-contamination risk difference?

In liquid phase storage, there is a theoretical risk that liquid nitrogen shared between containers could transmit microbiological contamination between samples. This risk is largely addressed by the use of closed carrier systems such as CBS high security straws, which prevent liquid nitrogen from entering the sample container. In vapour phase storage, samples are not in contact with liquid nitrogen and the cross-contamination pathway via liquid is eliminated.

Does vapour phase storage require different consumables?

Vapour phase storage places higher demands on the thermal performance of the cryosleeve, goblet, and cryocane – because samples in the vapour zone are not benefiting from direct liquid nitrogen contact. Cryosleeves used in vapour phase storage should provide additional insulation to protect samples during the brief period they are raised from the vapour zone into ambient air during retrieval.

A vapour phase vessel that has not had its temperature gradient mapped from liquid surface to top cane position is providing an unknown storage environment. Map it before you store clinical material in it.

Cryolab can advise on liquid and vapour phase storage configurations. Contact the team at cryolab.co.uk/contact-us/.