As is the case with all categories of laboratory equipment, the longevity of your freeze dryer depends on how you use it (application), how often you use it (frequency of use) and how well you care for it (maintenance). While it is true that some freeze dryers continue to lyophilize effectively for decades, the average life span of a freeze dryer in today’s laboratory environment is approximately 10 to 15 years.
Do you want to know the secrets to getting that much life out of your freeze dryer? Let’s break down application, usage and maintenance—all those factors that determine how long and how well your freeze dryer works—and identify several Do’s and Dont’s to guide you.
DO . . .
Make sure your freeze dryer is compatible with the eutectic temperature of your sample(s).
First and foremost, ensure your sample is compatible with your freeze dry system before you use the unit. A good rule of thumb is to plan for your most challenging sample and choose a system based on that need. It’s not possible to modify a freeze dryer’s condenser temperature. The condenser temperature should be 10 to 15°C below the sample’s eutectic point. Low freezing point solvents, for instance, should not be used on -50°C units. Certain acids should not be used with bare stainless steel and should only be used with PTFE models. Systems that reach -84°C are ideal for lyophilizing samples with low eutectic temperatures (like those that contain acetonitrile). Systems that reach -105°C can handle samples containing small amounts of ethanol.
Perform regular vacuum pump maintenance.
Have you ever had problems with your freeze dryer not pulling sufficient vacuum? If so, you’re not alone—it’s one of the most common freeze dry troubleshooting issues. The good news is that performing regular pump maintenance can help solve the problem, both reducing immediate downtime and increasing unit life in the long term. After you’ve ensured you have the appropriate lyophilizer for your samples (see above), do the same for your pump: standard rotary vane pumps work well for aqueous based solutions, and hybrid or combination pumps are best suited for use with solvents or acids. A low maintenance option, the scroll pump, is a new offering, which does not use oil at all. In some cases, secondary acid or solvent traps can be used to extend the life of your vacuum pump by providing an additional barrier between the lyophilizer and the pump. Dry ice traps are also available if you don’t have the appropriate temperature differential between the eutectic temperature of your sample and the collector temperature.
Last but certainly not least, make sure to change the oil in your vacuum pump every 1,000 hours (or sooner if your application warrants). If in doubt, check the appearance of the oil. If it’s cloudy or darker than an iced tea color, it needs to be changed.
Note that some pumps, such as hydrocarbon free scroll pumps, can pull a deep vacuum for freeze drying without using oil. If you’ve chosen a scroll pump, make sure to change the scrolls after every 40,000 hours of use.
Clean the freeze dryer after each run.
It’s necessary to defrost and drain the condenser after each standard run. If using acids, note that you’ll also need to neutralize the chamber. Regardless of the sample used, you must rinse and wipe down any components that may have come into contact with chemicals to reduce the risk of damage. Don’t let water—especially chemically contaminated water—sit on the stainless, acrylic or rubber components of your freeze dryer.
DON’T . . .
Put samples in the freeze dryer that aren’t completely frozen.
A sample must be completely frozen to be included in a lyophilization run. If it’s not, a large volume of the sample will evaporate, thereby producing a high initial vapor load. The vapors can then pass through the condenser and into the vacuum pump where they can do damage. Or, in worst-case scenarios, liquid could be sucked directly into the pump, causing even more damage.
Note that if a sample starts to melt back in-process, simply make adjustments so that is remains frozen or remove it from the system entirely.
Overload your freeze dryer.
Overloading your freeze dryer can make sessions last longer or even cause them to be wholly unsuccessful. The vapor load that the condenser must accommodate is the greatest when a sample is first loaded.
The instantaneous load capacity rating is the quantity of vapor a freeze dryer can accommodate at one time. This is a different measurement than the ice holding capacity or the 24-hour collection rating. When freeze drying multiple, large volumes, make sure the condenser temperature does not rise shortly after the sample is loaded. If this does happen, you are close to exceeding the instantaneous load capacity. In these instances, consider staggering the loading so samples are started at varying intervals.