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4. OPERATION PROCEDURES
Pre-freezing
For the pre-freezing process, freeze samples quickly and completely through, at a temperature
sufficiently lower than sample eutectic (solidification) point
*
. Freeze as thinly as possible so that
sample will not have a chance to melt before the drying process can dry it. Likewise, external heat
may influence and begin melting samples with a low eutectic table, if it is frozen too thickly in the
container.
Be advised that if throughput is too high, or if the eutectic point of samples is low, melting may give
way to sudden boiling (bumping) which may scatter samples.
When installing containers during a freeze-dry process, following pre-freeze, wait 3-4 minutes
(varies with container and sample types) before installing the next container and opening the
next valve for the next process, and so on until the whole process for all containers is complete.
Making intervals shorter between each individual container process or attempting to install all
containers at once, will cause samples to melt before vacuum pressure is able build again to dry
them.
Eutectic (solidification) Point
If pure water freezes at 0 degree Celsius, a mixed solution of water and other fluids may not
freeze immediately below 0 degrees Celsius, and may simply become soft ice, or not freeze at all,
because of being mixed with fluid(s) having a freezing point below 0.
If temperature continues to fall, the value at which the entire solution uniformly freezes solid is
called the “eutectic point” of that solution.
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