RETENTION CHARACTERISTICS OF OCTADECYLSILOXANE-BONDED SILICA AND POROUS POLYMER PARTICLE-LOADED MEMBRANES FOR SOLID-PHASE EXTRACTION

Forced-flow planar chromatography was used to determine the kinetic an d retention properties of an octadecylsiloxane-bonded, silica-based, p article-loaded membrane used for solid-phase extraction. The sorbent w as heavily loaded with bended phase resulting in a small intraparticle porosity. The large plate height and flow resistance indicates a hete rogeneous particle size distribution for the membrane with a significa nt fraction of below average size particles. The hydrophobicity and si lanophilic indexes and system constants in the solvation parameter mod el indicate similar retention properties to a common octadecylsiloxane -bonded silica cartridge sorbent under identical mobile phase conditio ns. The dimensional instability of a porous polymer particle-loaded me mbrane prevented its evaluation by forced-flow planar chromatography u sing the overpressured development chamber. Breakthrough volumes were determined for the porous polymer membrane under typical sample proces sing conditions for a number of solutes with varied properties and fit ted to a solvation parameter model. A comparison to data previously ob tained for an octadecylsiloxane-bonded, silica- based, particle-loaded membrane (Bakerbond) indicated that ease of cavity formation favors r etention by the octadecylsiloxane-bonded silica particle-loaded membra ne for non-polar and weakly polar analytes compared to the porous poly mer particle-loaded membrane. Significantly larger breakthrough volume s, however, are obtained on the porous polymer particle-loaded membran e for polar analytes. The porous polymer sorbent competes more effecti vely with water in dipole-type interactions and as a hydrogen-bond aci d. A solvent effect is speculatively suggested as the origin of the po rous-polymer sorbent's favorable retention of hydrogen-bond bases comp ared to the octadecylsiloxane-bonded, silica-based, material.