Polar amino acids are very often used as components of vitamin and supplement composition. Analysis of such complex composition is a challenging task. In this application, 5 amino acids (asparagine, glutamic acid, proline and arginine) and two preservatives (methyl paraben and propyl paraben) are separated on a Primesep 100 reversed-phase cation-exchange column with LC/MS compatible mobile phase. Method does not require ion-pairing reagent in the mobile phase. Compounds are monitored by ELSD and UV. Method is validated for quantitation of underivatized amino acids in complex mixtures. The method is simple and robust and can be used for analysis of various vitamin formulations.

Two underivatized amino acids, citrulline and arginine, are separated by mixed-mode chromatography on Primesep 100 and Primesep 200 HPLC columns with LC/MS compatible mobile phase. Method can be used for retention and separation of underivatized amino acids without ion-pairing reagent in the mobile phase.