Sucrose effect on reversed-phase liquid chromatography solute retention

The reversed-phase liquid chromatography retention of a series of benzoate ester molecules was investigated over a wide range of sucrose concentration s (c) 0.01-0.8 M using a C18 as the stationary phase;md a methanol-water mi xture with high organic fraction (60/40, v/v) as the mobile phase. A theore tical treatment was developed to investigate the effect of sucrose molecule s on the equilibrium between the solutes and the C18 phase and the metlhano l-water medium, respectively. This was found to be adequate to accurately d escribe the benzoate ester retention behavior when c varied. It was expecte d that the addition of sucrose was responsible for two main opposite contri butions to solute retention, (i) a net interaction between the solute and t he modifier in the mobile phase determining a decrease in k' values with c up to 0.2 M; and (ii) an increase in the solute affinity for the C18 statio nary phase due to the salting-out effect governing a retention increase abo ve 0.2 M. Thermodynamic parameter variations were calculated using van't Ho ff plots and discussed in relation to this retention model to confirm the r espective effects of the modifier on the solute affinity towards the two ph ases. (C) 2001 Elsevier Science B.V. All rights reserved.