Chromatographic separation of mixed peptides from amino acids in biological digests with volatile buffers

Two chromatographic methods, capable of separating mixed peptides from contaminating amino acids in biological digests, are described. Both methods involve separation on copper-Chelex resin, but each uses a different set of elution buffers. When separation method 1 was applied to a commercially available proteolytic digest of casein, the free amino acid content was reduced from 26.0% to 0.5%. With an enzymic digest of 14C-labelled proteins derived from plant biomass, separation method 2 decreased the contaminating free amino acids from 20.3% to 1.9%. Since the separated peptides are eluted with volatile buffers, they are suitable as substrates for biological experiments.