A study of the methylene/perfluormethylene selectivity of porous polymer monolithic stationary phases exhibiting different fluorous/hydrophobic content

Porous polymer monolithic columns are prepared from a variety of monomers and cross-linkers and can be customized to exhibit different selectivities for separate analyte classes. The composition of the monolith can be precisely controlled by selecting different monomers and or cross-linker ratios. In this work monoliths exhibiting both fluorous and hydrophobic character were prepared using butyl methacrylate and its fluorous analogue (monomer) and 1,3-butanediol diacrylate and its fluorous analogue (cross-linker) in different ratios. The selectivity of the monoliths was probed using capillary electrochromatography with several fluorous and alkyl benzene analytes. Hydrophobic stationary phases exhibited greater methylene selectivity (α−CH2−) while those with increasing fluorous character show enhanced pefluoromethylene selectivity (α−CF2−). The Gibbs free energy change associated with the sorption of the analytes on each stationary phase composition can be calculated from migration times (i.e. capacity factor) for the addition of an individual −CF2− or −CH2− moiety. Furthermore, the Gibbs free energy change associated with a single −CF2− or −CH2− moiety (analyte) interacting with an individual −CF2− or −CH2− (stationary phase) can also be estimated by plotting fluorous column composition against ΔG−CH2−⁡or CF2−0. Furthermore ΔG−CH2−0 and ΔG−CF2−0 can be plotted versus H2O percentage in mobile phase, and a new concept, hypothetical water percentage (HWP) is proposed to evaluate the hydrophobicity/fluorophilicity of a stationary phase.