Effect of triethylamine in the mobile phase on the retention properties ofconventional 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 polym eric 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 a nd analyzed by use of linear solvation energy relationships (LSER). Variati on of the resulting LSER coefficients - upsilon (hydrophobicity), r (polari zability), s (dipolarity), b (hydrogen-bond (HB) donating acidity), and a ( HB accepting strength) - were examined to see how TEA affects the intermole cular interaction properties of the mobile and stationary phases and hence the retention of the solutes. Addition of TEA to the mobile phase changes t he interaction properties of both conventionally polymerized and horizontal ly polymerited ODS; the effect is greater for the conventional phase. The H E donating acidity (b) of conventional polymeric ODS is significantly reduc ed by addition of TEA. For the mobile phases studied the magnitudes of the b and upsilon coefficients for the horizontally polymerized ODS phase are g reater than for the conventional phase. The different interaction propertie s of the two polymeric phases arise mainly as a result of differential adso rption of TEA, because of the very different amounts of surface silanol gro ups present on the two phases.