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Freeze Dryers: From Storage to Sample Preparation

Freeze drying faces new challenges in storage and sample preparation.

Mike May, PhD

Mike May is a freelance writer and editor living in Texas.

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Freeze drying faces new challenges in storage and sample preparation. In the past, researchers typically freezedried aqueous mixtures, but today’s samples might include solvents or alcohols.

As an example of sample preparation, Jenny Sprung, product manager at Labconco (Kansas City, MO), says, “For analysis using HPLC [high-performance liquid chromatography], samples are freeze-dried to a powder and reconstituted with another solvent that is compatible with the analyzer.” The freeze-drying might, for example, remove acetonitrile, and then the sample could be reconstituted with, say, methanol for analysis.

To improve efficiency, many users want to know when the endpoint, or dryness, is reached. “Determining 100 percent dryness can be difficult,” says Sprung, “but using tools on the freeze dryer allows you to monitor the conditions during a run. This includes product temperature probes, vacuum-pressure monitoring, or weighing the sample periodically during the process.” After freeze-drying, researchers can store the sample. Refrigerating hundreds of vials can be expensive, and room-temperature storage is more efficient. To simplify that process, Labconco developed a mini-stoppering chamber. “It allows you to stopper samples under vacuum for longterm storage without being exposed to moisture in the atmosphere,” Sprung explains. “This lets you easily stopper a few samples instead of using a large tray dryer, which can be very expensive.”

Systems for sharing

At Marquette University’s environmental laboratories (Milwaukee, WI), manager Michael Dollhopf and his colleagues freeze-dry small batches of microbial cultures, often from waste-treating and methane-producing biomass. “The main feature for our lab,” Dollhopf says, “is ease of use: push a few buttons and load the sample and go.” He adds, “We have multiple users, and it has to be a solid-state and easy-toreproduce, consistent function.”

Many users share a freeze dryer at Stanford University’s department of environmental earth system sciences, and they work with a wide variety of materials, from insects and plant tissues to soils and saliva, says lab manager Douglas Turner. In thinking about shopping for a freeze dryer, Turner says, “For us, it’s important that multiple users can have access to it at the same time, so we prefer the style with removable flasks versus the cabinet type.”

When sharing is not enough, freeze-drying can be outsourced to American Lyophilizer (Yardley, PA). This company works with customers to create a custom freeze-drying program. If a product does not require current good manufacturing processes (cGMP), American Lyophilizer even provides low-cost experimental runs that can be turned around in 24 to 48 hours. For lab directors interested in getting into freeze drying witth less of an investment, American Lyophilizer also offers used instruments.

Pushing ahead

Users have their own replacement guidelines. For instance, Dollhopf says, “For our use, the only time to replace would be if some major non-swappable component—probably the condenser—did not function.”

Turner notes, “Our freeze dryer is about 12 years old. Usually it’s the pump that needs attention. The seals of the unit can all be replaced, so I don’t think we would replace the unit until it no longer chills.”

To get the longest life, Sprung recommends keeping up with basic oil changes on the vacuum pumps, neutralizing the stainless steel from acids, and cleaning the collectors as you would on a refrigerator. In the end, a freeze dryer’s longevity depends on maintenance and care.

For additional resources on Freeze Dryers, including useful articles and a list of manufacturers, visit