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 and retention properties of an octadecylsiloxane-bonded, silica-based, particle-loaded membrane used for solid-phase extraction. The sorbent was heavily loaded with bended phase resulting in a small intraparticle porosity. The large plate height and flow resistance indicates a heterogeneous particle size distribution for the membrane with a significant fraction of below average size particles. The hydrophobicity and silanophilic indexes and system constants in the solvation parameter model indicate similar retention properties to a common octadecylsiloxane-bonded silica cartridge sorbent under identical mobile phase conditions. The dimensional instability of a porous polymer particle-loaded membrane prevented its evaluation by forced-flow planar chromatography using the overpressured development chamber. Breakthrough volumes were determined for the porous polymer membrane under typical sample processing conditions for a number of solutes with varied properties and fitted to a solvation parameter model. A comparison to data previously obtained for an octadecylsiloxane-bonded, silica- based, particle-loaded membrane (Bakerbond) indicated that ease of cavity formation favors retention by the octadecylsiloxane-bonded silica particle-loaded membrane for non-polar and weakly polar analytes compared to the porous polymer particle-loaded membrane. Significantly larger breakthrough volumes, however, are obtained on the porous polymer particle-loaded membrane for polar analytes. The porous polymer sorbent competes more effectively with water in dipole-type interactions and as a hydrogen-bond acid. A solvent effect is speculatively suggested as the origin of the porous-polymer sorbent's favorable retention of hydrogen-bond bases compared to the octadecylsiloxane-bonded, silica-based, material.