Anas Alshishani - depending on the number of samples you have, the format of those samples and the nature of the samples, different systems have different relative merits.

Common to ALL solutions - check solvent compatibility of the materials of construction and the vacuum pumps. Acetonitrile, where used, messes up plastic components really well. If you are drying all fractions (not just picking the samples containing the peaks for drying) then your initial solvent injection (presumably DMSO with a drop of methanol) will go right through with the solvent front. DMSO can mess up lots of plastics. Your modifier can also be aggressive, if not handled well - TFA is common. In addition, if you at any point use a basic modifier then you need to be careful of residual TFA in the dryer, when neutralised you can get fluoroacetate powder in everything!

Suggestions - use a DRY vacuum pump, to freeze dry, this means a scroll type. Not cheap, but pay once!

Use a cold trap / freeze dryer that has a temperature of below -70°C - needed to trap acetonitrile under vacuum. Don't use methanol as a co-solvent, you will need a liquid nitrogen trap to catch it.

If you are using a traditional freeze dryer - you need to freeze samples on the shelf to below -40°C ... or even -50°C when acetontirile is present. The sample itself (and the more you have, the more you see the effect) can inhibit freezing, or depress the freezing point of the liquid. If you have a "tree" or basic flask dryer - then a -80°C freezer is really the requirement for freezing the sample. In the basic dryer watch out for plastic parts, there are usually many. Even shelf dryers often have plastic doors.

Centrifugal evaporators with really deep vacuum and also really cold traps are expensive, good (I would say that - I work for the manufacturer) but expensive. Therefore if you have fewer samples and a more modest budget, a hybred approach may be useful, where volatile organic solvent is removed in a centrifugal evaporator and then the water is dryed in a freeze dryer. This works for some ... not all. Non-polar samples will crash out, so some co-solvent for freeze drying may be needed, such as T-Butanol - to help keep the sample in soluition.

Some suggested reading:

https://www.spscientific.com/Articles-And-Technical-Papers/ - and look for HPLC related papers - you need to scroll a bit

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

Kind regards,

Rob

Thank you you Rob, it is very useful information for my work

Hello,

Instead of freezedrying, I suggest using a Speedvac. For freezedrying you need to freeze your samples and, depending on the solventes, you will have different cryoscopic points.

Best regards

Thank you Sandra