1) I want to concentrate peptides and amino acids present in the liquid. Can i use ammonium sulphate preciptation? Will it works good?
2) Amino acid can be precipitated by changing the pH to isoelectric point but in my solution consists mixture of amino acids.Is it possible to change the pH to particular pH results precipitation of all kind of amino acids?
3) when i go through the literature, the TFA was used to change the pH to acidic and precipitate the amino acid by diethyl ether. Can i use any other acid and solvent instead of the above two?
You can lyophilize the peptides and aminoacids in a freeze dryer.
To deliver free amino acids from salts you can use propylene oxide as a reagent + small amount of methanol (as a solvent). The reaction is quantitative.
if you want salt free mixture, try to dissolve in few amount of DMF then precipitate with chilled ether. later you can do centrifugation or filter it. Wash well with ether then dry.. you would get peptide free form. it works even with amino acids, dipeptide or tripeptide. For better removal DMF traces try to sonicate with ether.. it works well.
Now if I understand your question correctly- you want to separate peptides from free amino acids. If this is the issue then you could think of using low nominal molecular weight cut off ultrafiltration membranes, e.g. 3000 Daltons or even as low as 1000 Daltons. If this is a one off concentration, you may think of using spin filtration cartridges which will permit rapid separation and concentration of peptides away from free amino acids. Finally two fraction could be easily free dried. Beauty of this process is that one does not need to add any solvents, acid etc.
I hope this is useful to you.
Regards
Tanoj
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