Effect of hypercrosslinking conditions on pore size distribution and efficiency of monolithic stationary phases

Three dihalogenic solvents differing in the length of alkyl chain (1,2-dichloroethane, 1,4-dichlorobutane, and 1,6-dichlorohexane) with three Friedel-Crafts alkylation catalysts varying in reactivity (AlCl3, FeCl3, and SnCl4) have been used to prepare hypercrosslinked poly(styrene-co-vinylbenzyl chloride-co-divinylbenzene) columns. Hydrodynamic characteristics as well as column efficiency and mass transfer resistance were tuned by the combination of swelling solvent and alkylation reaction catalyst in the modification mixture. The column swelled in 1,6-dichlorohexane and hypercrosslinked in the presence of AlCl3 provided the highest column efficiency and enabled fast isocratic separations of small molecules in a RP mode. To uncover factors controlling the efficiency of hypercrosslinked monolithic columns, we have studied pore volume distribution of prepared columns. We found that column efficiency increases with the higher pore volume of pores smaller than 2 nm.