Effect of column and mobile phase modifications on retention behavior in size exclusion chromatography of polycyclic...

Results are reported from a study, the goal of which was the reduction of the nonsize effects that govern the size exclusion chromatography (SEC) of planar polycyclic aromatic hydrocarbons (PAHs) on poly(divinylbenzene) (PDVB). Thought to arise from electron-pair donor--electron-pair acceptor (EPD-EPA) interactions between column packing and PAH eluate, nonsize effects could be substantially reduced by the addition of bulky substituents to the PAH, thereby perturbing EPD-EPA interactions between column and eluate. In this work we study the effect of adding a bulky substituent to the column material itself and have selected a sulfonated column material for this purpose. The-SO2OH group provides considerable steric shielding of the PDVB phenyl groups from the PAH eluates and thus its presence could weaken column-eluate interactions, but it is also electron-withdrawing and could possibly aggravate nonsize behavior, because the electron-pair acceptor strength of PDVB could be increased by electron-withdrawing substituents. It was found that either an increase or decrease of EPD-EPA bonding could result with the sulfonated PDVB (S-PDVB) columns, depending on the nature of the mobile phase. Size-dependent elution of PAHs could be obtained with S-PDVB for two classes of PAH by the inclusion of a small amount of hydrogen-bonding solvent, i.e. methanol, to the mobile phase. It is thought that the methanol additive, by strongly hydrogen bonding with the S-PDVB sulfonic acid groups, provides the additional steric shielding necessary to minimize EPD-EPA interactions.