Grafted MCM-41 materials are ordered mesoporous adsorbents suitable for reversed-phase liquid chromatography applications (RP-HPLC): they possess high surface area, which is a great advantage to enhance the thermodynamic behavior of the classical stationary phase by increasing solute retention. Hence, MCM-41s allow the separation of poorly retained solutes which are hard to separate on conventional silica gels. Furthermore, the ordered porosity in MCM-41 enhances the kinetic properties of the classical stationary phase. MCM-41s afford higher and more homogeneous molecular diffusivity, which increases the column efficiency for high flow rates as compared to that of classical silica-based columns. Besides, RP-HPLC provides a meaningful description of the particle size distribution at a macroscopic scale and of the pore ordering by probing the diffusivity of solutes. MCM-41s obtained by pseudomorphic synthesis of silica gel have successfully passed all the chromatographic tests and the results show that this new synthesis pathway really allows independent control of the pore size and the particle size of MCM-41. Spherical particles of 5 µm of MCM-41 without aggregation have been synthesized by this route and are revealed as very good candidates for stationary phases in RP-HPLC.

An acrylate monolith has been synthesized into a cyclic olefin copolymer microdevice for reversed-phase electrochromatography purposes. Microchannels, designed by hot embossing, were filled up with an acrylate monolith to serve as a hydrophobic stationary phase. A lauryl acrylate monolith was formulated to suit the hydrophobic material, by implementing 100% organic porogenic solvent. This new composition was tested in capillary prior to its transfer into the microfluidic device. Surface functionalization of the cyclic olefin copolymer surface was applied using UV-grafting technique to improve the covalent attachment of this monolith to the plastic walls of the microfluidic chip. The on-chip performances of this monolith were evaluated in detail for the reversed-phase electrochromatographic separation of polycyclic aromatic hydrocarbons, with plate heights reaching down to 10 microm when working at optimal velocity.

On-line comprehensive Reversed Phase Liquid Chromatography×Supercritical Fluid Chromatography (RPLCxSFC) was investigated for the separation of complex samples of neutral compounds. The presented approach aimed at overcoming the constraints involved by such a coupling. The search for suitable conditions (stationary phases, injection solvent, injection volume, design of interface) are discussed with a view of ensuring a good transfer of the compounds between both dimensions, thereby allowing high effective peak capacity in the second dimension. Instrumental aspects that are of prime importance in on-line 2D separations, were also tackled (dwell volume, extra column volume and detection). After extensive preliminary studies, an on-line RPLCxSFC separation of a bio-oil aqueous extract was carried out and compared to an on-line RPLCxRPLC separation of the same sample in terms of orthogonality, peak capacity and sensitivity. Both separations were achieved in 100min. For this sample and in these optimized conditions, it is shown that RPLCxSFC (with Hypercarb and Acquity BEH-2EP as stationary phases in first and second dimension respectively) can generate a slightly higher peak capacity than RPLCxRPLC (with Hypercarb and Acquity CSH phenyl-hexyl as stationary phases in first and second dimension respectively) (620 vs 560). Such a result is essentially due to the high degree of orthogonality between RPLC and SFC which may balance for lesser peak efficiency obtained with SFC as second dimension. Finally, even though current limitations in SFC instrumentation (i.e. large extra-column volume, large dwell volume, no ultra-high pressure) can be critical at the moment for on-line 2D-separations, RPLCxSFC appears to be a promising alternative to RPLCxRPLC for the separation of complex samples of neutral compounds.