Zwitterionic stationary phases with nearly identical capacities were prepared by graft polymerization of a series of sulfobetaine precursors onto the surface of porous PS/DVB particles. The different spacer lengths are used as an investigative tool for the retention behavior of carboxylic acids; namely malonic, succinic, glutaric and maleic acid. In zwitterionic ion chromatography-hydrophilic interaction liquid chromatography (ZIC-HILIC) separation mode, the retention characteristic of carboxylic acids was examined using sodium acetate/acetonitrile eluents and UV detection. The retention is based on partitioning in reversed as well as in HILIC mode and zwitterionic ion exchange resulting in a mixed separation mode for the carboxylic acids. This ion exchange behavior has never been observed before for sulfobetaine-based zwitterionic stationary phases.

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