Labconco FreeZone Plus 4.5 Liter and FreeZone -105 C Cascade Freeze Dry Systems 73870 Series - Manual (Page 24)

Chapter 4: Using Your Freeze Dryer
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Setting the Operating Vacuum Level
The vacuum level may be set by the user to optimize the freeze dry process.
Normally, the sublimation rate will increase if there is less vacuum (a higher
pressure) in the freeze dryer. A good starting place is to set the vacuum so its
level is equivalent to about 10°C colder than the eutectic or collapse
temperature of the sample. Adjustments to the vacuum level must be made
for various freeze drying conditions. Factors that must be considered are
whether the sample is freeze dried on heated shelves or in glassware attached
to manifold valves, the volatility of the sample itself, the size of the sample
and the heat energy supplied to the sample.
Some guidelines for setting the freeze dryer are shown below. These show
pre-freezing temperatures and vacuum levels. Exact protocols must be
determined by the user for the specific samples that are being freeze dried.
When the vacuum control is set to operate at less vacuum, the ice holding
capacity of the collector may be decreased.
Material
Solidification/Eutectic
Temperature
Pre-Freeze
Temperatures
Vacuum Set Point
Bacteria,Virus -40°C and Colder -50°C &
Colder
0.040 mBar &
Lower
Milk -5 to -13 -15 to -23 1.65 to 0.77
Fungi -40 and Colder -50 & Colder 0.04 and lower
Vegetable Tissue -25 to -50 -35 to -60 0.22 to 0.01
Human Tissue -30 to –40 -40 to –50 0.12 to 0.04
Blood Plasma -10 to –25 -20 to –35 1.03 to 0.22
Vaccine -30 to –40 -40 to –50 0.12 to 0.04
Pre-Freezing Samples
Appropriate containers for freeze drying include ampules, serum bottles, and
wide-mouth freeze drying flasks. Shell freezing of samples is recommended
for wide-mouth freeze drying flasks. Smaller samples in ampules and serum
bottles may be frozen in a freezer or in the center of the collector chamber.
The sample container size should always be at least two to three times the
sample size (i.e., 40 ml samples should be prepared in 80 ml containers or
larger). The temperature required for pre-freezing is dependent on the
characteristics of the sample. Pre-freezing temperature typically is at least
10° to 20°C below the eutectic or collapse temperature of the sample.