Effect of triethylamine in the mobile phase on the retention properties of conventional polymeric and horizontally polymerized octadecylsilica in RPLC

The effect of triethylamine (TEA) in the mobile phase on the RPLC retention behavior of small organic solutes has been studied on a conventional polymeric octadecylsilica (ODS) and on a horizontally polymerized ODS. Retention factors for a set of solutes were measured on the two phases with methanol-water mobile phases containing triethylamine at different concentrations and analyzed by use of linear solvation energy relationships (LSER). Variation of the resulting LSER coefficients - upsilon (hydrophobicity), r (polarizability), s (dipolarity), b (hydrogen-bond (HB) donating acidity), and a (HB accepting strength) - were examined to see how TEA affects the intermolecular interaction properties of the mobile and stationary phases and hence the retention of the solutes. Addition of TEA to the mobile phase changes the interaction properties of both conventionally polymerized and horizontally polymerited ODS; the effect is greater for the conventional phase. The HE donating acidity (b) of conventional polymeric ODS is significantly reduced by addition of TEA. For the mobile phases studied the magnitudes of the b and upsilon coefficients for the horizontally polymerized ODS phase are greater than for the conventional phase. The different interaction properties of the two polymeric phases arise mainly as a result of differential adsorption of TEA, because of the very different amounts of surface silanol groups present on the two phases.