CO2-modified solvents for chromatographic separationElectronic supplementary information (ESI) available: Table of analytes and supporting experimental results. See DOI: 10.1039/c6gc03405e

Developing alternatives to organic solvents and salts in chromatographic separation is highly desired. CO 2 is abundant, inexpensive, nontoxic, environmentally benign, and easily removed. In this work, the impact of CO 2 -modified aqueous solvents on reversed phase chromatographic separation is studied. A robust custom CO 2 delivery system (1 bar CO 2 ) is able to provide CO 2 -modified aqueous solvent with pH 3.9-6.5. A significant hydrophobicity switch of the stationary phase was observed by a reduction in the retention factor, k , when using CO 2 -modified solvents for the diethylaminoethyl (tertiary amine) and polyethylenimine (primary, secondary and tertiary amine) functionalized columns. In particular, the polyethylenimine column can be used to perform separation with 100% water without any organic solvent added. Carboxymethyl based columns were not switched by CO 2 -modified solvent, indicating the need for more significant pH change. The CO 2 triggered selectivity switch resulting from analyte ionization provides an important tool in controlling the selectivity of separation. Overall, CO 2 -modified solvent is valuable in tuning the elution strength and selectivity of reversed phase chromatography. CO 2 modified mobile phases are used to adjust the retention factor of compounds on (primary, secondary and tertiary amine) functionalized columns.