Dear Vibert,

Was the not dry tube in the middle of the pack? If so, the cold tubes all about it will make it dry more slowly.

Was every tube normalised? Plasma is a natural product [mine will be different to yours] and if there are more lipids in the failed sample (especially if they float) then this can be a problem.

With regards to reprocessing the question is whether the sample is OK now. If it is, then DILUTE it with WFI before you try and freeze it again. The higher concentration the more difficult it is to freeze.

A good general guide to freeze drying is available here:

https://www.spscientific.com/freeze-drying-lyophilization-basics/

Kind regards

Rob

Dear Mr. Rob Darrington,

thank you for your answer.

The failed tube was on a border, moreover, samples were kept at -80°C for nearly 2 hours before freeze-drying, and they were all frozen.

I will try then to dilute it, as you proposed. However, even in the case that this sample had a too high lipid-concentration, I left the freeze-dryer turn over the weekend, so quite long, and it should have been enough even for very lipidic samples, don't you think?

Thanks again,

Laëtitia

Check out: MacKenzie, A. P. Inter Symposium on Freeze-Drying Biol Products (1976) - this is the leading work on Plasma freeze drying. I believe the cycle is 96 hours.

Kind regards

Rob