Separation and Detection of Underivatized Amino Acids

Abstract

Abstract Amino acids (AA) are separated on a Hamilton PRP-1 polystyrene divinylbenzene column with a basic CH3-CN:H2O mobile phase containing a tetraalkylammonium (R4N+) salt and a detector active counteranion. The underivatized AA are retained and separated as anions via a competing anion exchange process that occurs between the AA anion and the counteranion towards the R4N+ salt, an equilibrium amount of which is maintained on the stationary phase according to the mobile phase conditions. An indirect detection (ID) is possible because of displacement of the detector active counteranion. Indirect photometric (IPD), fluorometric (IFD), or electrochemical (IED) detection is possible by using a counteranion that absorbs, fluoresces, or is electrochemically active. Parameters that influence retention and resolution are AA side chain structure and mobile phase pH. R4N+ structure and concentration, organic modifier, and counteranion selectivity and concentration. These same parameters, in addition to the count...