I have small volumes of protein samples that were precipitated by ammonium sulfate then dialyzed. Now I want to concentrate the protein samples, the method I have found so far are centrifugal filter and freeze drying. It seems methods are on the costly side. I am looking for a less costly method, any suggestions please?
Freeze drying doesn't cost anything as long as you don't have to buy the lyophilizer or pay for the electricity.
Anyway, another way to concentrate the protein is to leave it in the dialysis bag and then bury the bag in a water-absorbent resin, such as carboxymethylcellulose. This draws solvent out of the bag. People also use concentrated high-molecular weight PEG solutions for this purpose.
Just a bit more info will help. How many samples, tens of samples or less? How much volume is "small volumes", sub-milliliters or milliliters? How many fold is the concentration? What is the next step after concentration; does your final objective require native conformtion? Is the freeze drying method you found the Savant SpeedVac?
Since the protein is already dialyzed, some strategies can be fast, convenient, controlled, and inexpensive but the answers to the above questions will help to decide. For example, you could batch-wise bind and step elute using a small amount of a reversed phase media/solvent volume then evaporate off the solvent, or use the same concept with an affinity media, or the same concept with an ion-exchanger but do bind release with pH control without salts, or precipitate the protein with organic solvent and then isolate the pellet followed by dissolution, or pH precipitate followed by pellet isolation and dissolution to the desired volume. However, some of these approaches may leave your protein denatured but that may not matter depending upon your objective.
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