Effect of the solvent on the chromatographic selectivity in reversed-phase and HILIC

In this work, the characterization of several reversed-phase and HILIC chromatographic systems is presented by means of the Abraham's solvation parameter model, focusing on the impact of solute polarizability, dipolarity, hydrogen bonding, and molecular volume on chromatographic retention. Although retention times in octadecylsilane columns are clearly dependent on the nature and content of the organic modifier in the mobile phase, similar chromatographic selectivities are reported for eluents containing acetonitrile or methanol in the range between 40 and 80%. The most relevant analyte properties affecting retention are the hydrogen bond acceptor capacity and the molecular volume, the former favoring partition into the mobile phase and the latter into the stationary phase. The behavior of HILIC systems greatly depends on the nature of the support (silica or polymeric), the bonded phase (zwitterionic, aminopropyl, dihydroxypropyl) and the organic solvent used in the eluent (acetonitrile or methanol), but they have in common that larger solute volumes allow more favorable partition into the organic solvent-rich mobile phase. The evaluation of the chromatographic retention of ionized analytes in HILIC should be performed with care, since they may interact with ionized buffering species, leading to unexpected lower retentions.