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.

GABA (neurotransmitter) and its isomers are polar zwitter-ionic compounds. Due to the position of amino-groups, all three compounds show different polar and basic properties. The isomers of aminobuturic acid are separated on an Obelisc N HILIC/cation-exchange column. Buffer concentration has a different effect on retention of alpha-, beta-, and gamma-aminobutyric acid. This general and robust method can be used for separation of other polar and ionizable compounds and isomers by mixed-mode chromatography.

Amino acids are essential components of numerous formulation. Health supplements can contain various amino acids and vitamins and require quantitation of each ingredients. Amino acids are very polar compounds with limited or no retention in reversed-phase chromatography. The most common approaches are reversed-phase chromatography with ion-pairing reagent and hydrophilic interaction chromatography (HILIC). Underivatized amino acids can be retained by combination of reversed-phase and cation exchange mechanism on Primesep 100 mixed-mode. Retention time is controlled by amount of acetonitrile, buffer and buffer pH. Method does not require ion-pairing reagent. This method is for UV detection. LC/MS, ELSD or Corona CAD can be employed for analysis of amino acids with trifluoroacteic acid or ammonium formate in the mobile phase. This approach can be used for HPLC analysis of all underivatized amino acids.

Glutamic acid and GABA are neurotransmitters. Glutamic acid and GABA are non-essential amino acids. They are hydrophilic and zwitter-ionic in nature . At lower pH, carboxylic acid groups of amino acids are not ionized, making them more hydrophobic and basic. Underivatized glutamic acid and GABA were retained and separated on a Primesep 100 column using ACN/water/TFA mobile phase. Amino acids can be monitored by low UV or ELSD/CAD. Retention is provided by reversed-phase and cation-exchange mechanism. Method can be used for analysis of underivatized amino acids in various matrices including supplements, vitamin and other complex mixtures. various mobile phase can be used with corresponding detection techniques.