I am doing lots of proteomics and hence I often times perform speed vac. I do not want to dry my samples completely, but I want a certain fixed volume left (lets say 100ul). Has anyone found a way to achieve this? I mean you start speedvac you come back overnight and you have exactly 100ul of solution in all tubes.
Hello Pavel, I would recommend you to do a few test runs to estimate how much time it takes to remove desired amount of solvent using your speedvac system. Then you could program it to stop after this time.
Hi Pavel, add glycerol to your samples, 100ul glycerol per sample. Glycerol will not evaporate in a speed vac.
If you think about your goal, you are really only trying to concentrate your sample. Unfortunately evaporation like this isn't an easily controlled process. My recommendation (especially for best reproducibility) is to run the speedvac until the samples are fully dried, and then add water (or a known buffer) back to get the volume you want. However, if you are truly trying to avoid complete drying (e.g. if you end up with denaturation, aggregation, hard to redissolve, etc.), the glycerol suggestion would be useful, but you must be certain that the glycerol will not interfere with your downstream work. Or consider a completely different method: you could use centrifuge filters to concentrate your sample (Amicon is one brand, and there are others). In some of my own previous proteomics work, I used such filters with excellent results. And in general I would say this is much faster than evaporation also.
I agree with Dr. Gelfand, I also had good experience using Amicon or Vivaspin for concentration of samples.
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