Demonstration of simultaneous cation-exchange and reversed-phase mechanisms on a strong-acid cation-exchange column

Demonstration of simultaneous anion-exchange and reversed-phase behavior on a strong anion-exchange column

We demonstrate in this report that a conventional silica-based strong anion-exchange column can exhibit reversed-phase chromatographic behavior simultaneously with ion-exchange in a methanol-aqueous phthalate mobile phase. Reversed-phase behavior is shown for PAHs in relatively high methanol-content mobile phases, while polar organics exhibit reversed-phase behavior in 0-10% (v/v) methanol-water eluents. At low concentrations (0-10% v/v) methanol has little or no effect on anion retention, while the anions exhibit only slight increases in retention in 60-80% (v/v) methanol at near-neutral pH values. Likewise, pH changes used to manipulate anion retention have essentially no effect on PAH retention, and cause only small decreases in retention for most of the polar organics studied. Little or no pH-effect was seen on a phenyl column (no exchange group) or with acetate mobile phase. It is shown that manipulation of pH and methanol content allows the grouping of neutral organic analytes early in a chromatogram, followed by the anions, with no class overlap. Several example chromatograms are given, including that of a red wine sample. Column efficiency was good for anions but only modest for organics.