The low boiling point of -196°C liquid nitrogen and its volatile characteristics determine that when it is used as a freezing medium, it needs to be replenished regularly even if it is placed in a double-layer insulated sample storage tank. To replenish liquid nitrogen, you can either choose a gas company or prepare a tank that already contains liquid nitrogen and pour it in yourself or use a pump or liquid nitrogen supply tank.
Everyone is familiar with these methods, but some users, especially those who have new needs for sample freezing and encounter the situation of rehydration during use for the first time, may worry that adding liquid nitrogen directly will affect the sample, and they will want to first add it when adding liquid nitrogen. Take out the sample.
Is this the right thing to do?
In fact, no need!
Compared with the possible fluctuations when adding liquid nitrogen, the transfer will have a greater impact on the sample.
The sample is stored in a liquid nitrogen storage tank in a liquid phase, that is, the sample is always soaked in liquid nitrogen and maintains a stable freezing temperature of -196°C. The standard for adding liquid nitrogen is when the liquid nitrogen cannot cover the highest point of the sample. In this case, the sample is always in an environment of around -190°C, and there are freezing racks, freezing boxes, round buckets, or other sample storage containers to prevent liquid nitrogen from directly contacting the internal samples. Adding liquid nitrogen will not cause large liquid or temperature fluctuations to affect the sample, and it is very stable.
But if it is transferred out, on the one hand, it is necessary to equip another liquid nitrogen sample storage tank with a comparable capacity as a backup. More importantly, all the samples need to be taken out, that is, the samples at the bottom must also be exposed to the air together with the rack or bucket. , contact with heat is unavoidable. When the sample volume is large, the sample will be exposed to more air, and the temperature will change even more, which is not conducive to the sample.
Therefore, there is no need to take out the sample when filling the liquid nitrogen sample storage tank with liquid nitrogen!