Phosphonium-based ionic liquids in electrokinetic capillary chromatography for the separation of neutral analytes

In this work we elucidated the applicability of phosphonium-based ionic liquids (ILs) as pseudostationary phase in electrokinetic capillary chromatography (EKC) with UV-detection. The phosphonium ILs studied contain bromide, chlorine, or tosylate ions, as counter ions, and alkyl side chains of variable length on the phosphorous atom. The effects of the type and concentration of the IL, pH, ionic strength, and type of background electrolyte solution on the electroosmotic flow (EOF) and on the effective electrophoretic mobilities of some neutral model analytes were investigated and large variations in the migration times were observed. Especially the IL employed remarkably affected the strength and direction of the EOF Successful separations were obtained for neutral aromatic singly substituted analytes, namely benzene, toluene, phenol, and nitrobenzene. The results demonstrated the potential of capillary electromigration methods for rapid interaction studies between ILs and analytes, which is useful for the development of novel materials for sample preparation and separation purposes or for novel catalyst and chemical processing studies.

► Strong EOF reversal using ILs with one long chain alkyl chain (C14 or C16).
► Separation of neutral aromatic compounds using phosphonium-based ionic liquids as carrier in EKC.
► Baseline separation of the studied compounds with 2.5 mM IL concentration.
► Good separation with BGEs at pHs 6–9.
► Higher UV sensitivity using phosphate than HEPES BGEs.