Four underivatized amino acids (serine, methylserine, GABA and methionine) were separated on a Primesep 100 reversed-phase cation-exchange mixed-mode HPLC column. Two methods, one for UV and one for ELSD/LC/MS show good separation and peak shape for underivatized amino acids. This column and general HPLC approach can be used for analysis of underivatized amino acids. Primesep 100 is designed to replace reversed-phase HPLC column in combination with ion-pairing reagents.