The Labconco FreeZone 6 Liter Freeze Dry System is used in our laboratory primarily for lyophilization of small volumes (1-5 ml) of plant extract. Freeze-drying removes water or other solvents from samples and can be effected by parameters such as temperature and pressure. The apparatus consists of a vacuum pump (lowers the pressure surrounding the sample), a collecting system and a cold trap (collects moisture coming from the sample). The vacuum pressure from the pump removes gases from the samples, while the collector (lower pressure than the sample) condenses the gases. The upright stainless steel collector coil is capable of removing 4 liters of water in 24 hours. The 3⁄4 hp, CFC-free refrigeration system is able to cool the collector to –50 C pretty quickly. Overall dimensions of the freeze dryer are 31.8” w, 28” d, and 36.3” h, so it requires some space in the lab.
Our liquid samples need to be pre-frozen (below eutectic temperature), since our protocols require transition from solid to gas phase. If liquid remains in the sample following pre-freezing, you can see sample movement in the flask towards the adaptor, which can lead to loss of material during the process. We pre-freeze our plant extracts in lyph-lock flasks (compatible with the freeze dryer) or in vials without tops, which we put inside the lyph-lock flasks. The lyph-lock flask consists of a borosilicate glass top and bottom with a rubber separator ring. Adaptors are required to attach the flasks to the freeze dry valve ports. We have the externally-attached 12-port drying chamber, which can accommodate different flask sizes via adaptors (drying chamber purchased separately).
For our purposes, we use the manifold method where flasks containing individually prefrozen samples are attached to the ports of a manifold. One advantage with this method is the direct connection of the flask to the upright collector and subsequent evaporative cooling to maintain efficient, low sample temperature. Another advantage with this manifold is that one can freeze-dry many different samples simultaneously while still being able to independently manipulate individuals based on drying times. This system minimizes possible contamination compared to other methods, such as batch or bulk methods, however one disadvantage is that only limited sample volumes can be dried.
The LCD reader provides digital readouts of temperature and vacuum, total hours for both of theses parameters and any alarm message (while sounding an audible signal as well). Conveniently, there is a temperature graph display (monitors the collector temperature with 6 LED indicators from +10 to -40 C) and a vacuum graph display (shows the system vacuum level with 6 LED indicators from 2 to 0.12 mBar). The vacuum control valve speeds the evaporation process by maintaining the proper vacuum level, while the upright collector chamber coupled with an extendable drain hose makes defrosting and cleaning easy. Also, a unique protective feature is the moisture sensor, which prevents damage to the vacuum pump by detecting moisture in the collector chamber, thus preventing refrigeration or vacuum initiation. The vacuum break valve prevents oil back-streaming and there are easy-to-follow operating instructions printed on the front of the machine. The user has the option of either automatic or manual refrigeration modes. In manual mode, only the refrigeration is initiated, while automatic mode the vacuum pump is activated when the collector temperature reaches -40 C. When the temperature graph display reaches -40 and the vacuum graph display reaches 0.12 mBar, then one can attach the flask to the port.
We found the FreeZone 6 Liter Freeze Dry System to be a great freeze-dryer to lyophilize our plant extracts quickly (3-4 hours to lyophilize 1-2 ml of sample). For a machine of this size, it is very quiet and requires little maintenance. The only disadvantage is the relatively large footprint, but one can purchase the smaller bench top models as an alternative.
Hee Chul Lee, Ph.D.
Post-doctoral scientist
Dept. of Biochemistry
NYU School of Medicine