7. When the program is complete, transfer the canes to boxes
in the vapor phase of a liquid nitrogen unit for storage. If the
unit is more than a few feet from the programmable freezer,
transport the canes in an insulated container with liquid nitrogen.
Be careful not to store the vials directly in liquid nitrogen. See
notes under “Safety” below. Liquid nitrogen has a temperature of
–196ฐC. The vapor will have a temperature gradient which is near
–196ฐC at the level of the liquid and which gradually becomes
warmer near the top of the freezer. For best long-term storage,
keep frozen materials below –130ฐC. To ensure that materials
are stored at proper temperatures, liquid nitrogen freezers must
first be validated by placing a thermometer at the top of the
unit and adding liquid nitrogen until a working temperature of
at least –130ฐC is maintained at the top of the freezer. This level
is then continuously monitored and an alarm system activated
if the levels fluctuate above or below predetermined limits.
Occasionally, strains may require special handling. If a strain does
not survive freezing in glycerol, try 5% DMSO. Some cultures, such
as some Agaricus strains, may be grown on sterile seeds, grains or
pollen, and may be frozen without a cryoprotectant.
7. When the program is complete, transfer the canes to boxesin the vapor phase of a liquid nitrogen unit for storage. If theunit is more than a few feet from the programmable freezer,transport the canes in an insulated container with liquid nitrogen.Be careful not to store the vials directly in liquid nitrogen. Seenotes under “Safety” below. Liquid nitrogen has a temperature of–196ฐC. The vapor will have a temperature gradient which is near–196ฐC at the level of the liquid and which gradually becomeswarmer near the top of the freezer. For best long-term storage,keep frozen materials below –130ฐC. To ensure that materialsare stored at proper temperatures, liquid nitrogen freezers mustfirst be validated by placing a thermometer at the top of theunit and adding liquid nitrogen until a working temperature ofat least –130ฐC is maintained at the top of the freezer. This levelis then continuously monitored and an alarm system activatedif the levels fluctuate above or below predetermined limits.Occasionally, strains may require special handling. If a strain doesnot survive freezing in glycerol, try 5% DMSO. Some cultures, suchas some Agaricus strains, may be grown on sterile seeds, grains orpollen, and may be frozen without a cryoprotectant.
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