I freeze dry bacterial suspensions using an old shelf freeze dryer. I freeze my suspensions in a -80oC freezer overnight before transferring samples on to the shelves of a drying chamber which is mounted on to the condenser chamber(cold trap) of the freeze drier. The condenser chamber can reach a maximum temperature of -53oC only. The suspensions move up the vials (containers), melt, bubble and pour off when vacuum is applied. I have been thinking that may be I freeze the suspensions at a temperature higher than that of the condenser chamber because I learnt that the product temperature should be warmer than that of the cold trap.
Dear Sandu,
It sounds like there is some melting of the sample, either due to thawing during transfer or, the pressure is not low enough in your system to keep the ice frozen during sublimation.
Resoluitions:
Pre-freeze the shelves before transfer, and ensure that the drying method is to draw a good vacuum before adding any heat to speed drying
Ensure that the vacuum level is adequate to have the ice sublime below the freezing point for your mixtures. The other things you are likely to add (buffer salts, cryo preservation sugars etc.) to your sample can act like an antifreeze.
A general guide to freeze drying can be found here:
https://www.spscientific.com/freeze-drying-lyophilization-basics/
Kind regards,
Rob
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