Labconco FreeZone Triad Freeze Dry System 74000 Series - Manual (Page 6)

Chapter 1: Introduction
Product Service 816-333-8811 or 1-800-522-7658 2
Table 1
Freeze Dry Rates
The efficiency of the freeze drying process is dependent upon the surface
area and the thickness of the sample, the collector temperature and vacuum
obtained, the eutectic point and solute concentration of the sample. It is
important to remember these factors when trying to obtain efficient
utilization of your freeze dry system. A listing of selected materials and their
approximate drying times are shown in Table 1 for your reference.
Safe Temperature and Drying Times for Selected Materials
Material 10mm
Thick
Safe
Temperature °C
Collector
Temperature °C
Hours
(Approx.)
Milk -5 -40 10
Urea -7 -40 10
Blood Plasma -10 to -25 -40 16
Serum -25 -40 18
Vaccinia -30 to -40 -50 22
Influenza Vaccine -30 -50 24
Human Tissue -30 to -40 -50 48
Vegetable Tissue -50 -80 60
*Total sample quantities are contingent on various Triad Freeze Dry System capacities.
Up to the point of overloading the system, the greater the surface area of the
sample, and the faster the rate of freeze drying. By contrast, for a given
surface area, the thicker the sample the slower the rate of freeze drying. This
is based on the fact that the heat of sublimation is usually absorbed on one
side of the frozen sample and must travel through the frozen layer to vaporize
water at the other surface. In addition, as the sample is freeze dried, the
water vapor must travel through the layer of dried material. The thicker the
sample, the greater the chance that the dried layer may collapse which would
cause an additional decrease in the rate of freeze drying.
The surface area and thickness of the sample can usually be ignored when
each sample contains only a few milliliters. However, for larger volumes, the
samples should be shell frozen to maximize the surface area and minimize
the thickness of the sample. The volume of the freeze dry container should
be two to three times the volume of the sample.
In order for lyophilization to occur, ice must be removed from the frozen
sample via sublimation. The collector and the vacuum pump accomplish this.
The collector, which should be at least 15 to 20°C colder than the eutectic
temperature (melting temperature) of the sample, traps vapor as ice. Since
the vapor pressure at the collector is lower than that of the sample, the flow
of water vapor is from the sample to the collector.
Since this vapor diffusion process occurs very slowly under normal
atmospheric conditions, a good vacuum is essential to maintain an efficient
rate. In many applications, the maintenance of a vacuum of 0.133 mBar or
less is recommended.