Freeze drying, or lyophilization, is a time consuming process that can be easy or difficult depending on the sample type, sample size and requirements. Using accessories designed for specific samples and challenging applications helps make lyophilizing these samples easier.
When samples are stoppered under vacuum, their shelf life is increased dramatically. Placing airtight seals on the vials before they are exposed to the atmosphere where they can absorb moisture keeps the samples drier. Stoppering under vacuum is determined by your quantity and budget. There are three choices, and deciding which to use depends on the size and number of samples you have.
The first option is a stoppering tray dryer. Although they require a substantial investment, stoppering tray dryers can handle large quantities of samples and offer sophisticated programming capabilities. The FreeZone® Stoppering Tray Dryer has three temperature-controlled shelves (-40° C to +40° C) with 588 square inches of area on which to place samples, which can hold up to four hundred 2 ml serum bottles.
The second option, less expensive than the first, is a stoppering chamber or shelf, which connects to the collector like a drying chamber. Essentially, it is a clear chamber with two heated shelves (+40° C) that provide 158 square inches of area. The Clear Stoppering Chamber has a handle that, when turned, applies pressure to the shelves, collapsing them onto one another and pushing the stoppers into the vials. It holds fewer samples than the FreeZone Stoppering Tray Dryer and uses a more manual process, but the Clear Stoppering Chamber makes sense if your stoppering needs are infrequent or on a smaller scale.
The smallest and most economical accessory for stoppering under vacuum is the Mini Stoppering Chamber. This small chamber connects directly to the valve of a drying chamber or manifold like a flask. It has an area of approximately 18 square inches and is ideal for very small sample sizes or just a few samples that need to be stoppered. It accommodates small bottles and has a capacity of up to forty-eight 2 milliliter bottles or eight 30 milliliter serum bottles. Paired with an isolation valve and a clean bench, the Mini Stoppering Chamber can make stoppering under vacuum in a sterile environment easy.
Unfortunately, sample melt back occurs frequently with several common sample types. The best way to prevent sample melt back is to limit the heat transferring into the sample. This is difficult when freeze drying in a flask, as the heat input is essentially the room temperature that cannot be easily regulated.
Labconco offers Flask Holders that insulate a sample by holding a sample flask inside a larger flask. This creates an even air gap around the sample flask and slows the heat transfer from the room air to the sample.
Alternate options to avoid sample melt back are to insulate the sample container with other materials. A flask can be wrapped with any sort of insulating material, such as packing foam, to create a barrier between the sample and room atmosphere. For samples in a tube, simply place the tube in a flask, fill the flask with water and freeze the entire flask. This creates an insulation of ice all the way around your sample that will lyophilize with your sample.
Ampules are glass tubes that are made for very small samples that will be heat sealed under vacuum. Traditionally, ampules are used for long-term storage making it critical they are sealed under vacuum. Due to their size, special accommodations must be taken when connecting them to the collector and it is difficult to lyophilize large numbers of samples at the same time.
A new option is an Ampule Pod (pictured at right), which connects to a valve and has separate tubes that hold ampules allowing 15 ampules to be freeze dried at once!
Samples in microplates can be difficult to freeze dry. Because of their very small size (<1 ml), they are prone to melt back during transfer from the freezer to the freeze dryer and when establishing deep vacuum levels.
Labconco’s new Microwell Plate Holder can help! The molded aluminum block provides a solid mass for better temperature regulation and conduction. The design eliminates the air gap between the bottom of the plate and the freeze dryer’s shelves ensuring good heat conduction throughout the run and reducing the run time. By pre-freezing the entire block, there is more mass around the samples, which insulates and keeps them frozen until reaching deep vacuum.
Freezing a sample in a flask at an angle has several advantages over freezing a sample in an upright flask (stub freezing).
The Slant Freeze Flask Holder keeps liquid samples at an angle when pre-freezing. Because liquid expands when freezing, the angled sample puts less pressure on the flask than stub freezing to help prevent the glass from breaking. It also allows for faster freeze drying by increasing the surface area and putting more of the sample in contact with the glass for better heat transfer.
Each freeze drying sample type presents unique challenges, but the right accessories can make the job easier. Labconco is here to help you find solutions to your freeze drying dilemmas.
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