Dansyl amino acid enantiomer separation on a teicoplanin chiral stationaryphase: effect of eluent pH

The retention and separation of a series Of D,L dansyl amino acids (used as test solutes) on a teicoplanin stationary phase were investigated over a w ide range of mobile phase (citrate buffer-methanol, 90:10. v/v) pH. An appr oach based on the development of various equilibria was carried out in orde r to describe the retention behavior of the solute in the chromatographic s ystem. The equilibrium constants corresponding to the transfer of the anion ic and zwitterionic forms of the dansyl amino acids from the mobile to the stationary phase were determined. These values allowed one to explain the d ecrease in the retention factor and the associated increase in the separati on factor as the eluent pH was increased. Thermodynamic parameter variation s were calculated so that the driving forces of the solute association with the teicoplanin phase were derived. This approach indicated that the chira l discrimination was principally controlled by the interaction between the anionic form of the solute and the stationary phase. (C) 2001 Elsevier Scie nce BM All rights reserved.