title: Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention.
abstract: Since water associated with the stationary phase surface appears to be the essence of the retention mechanism in hydrophilic interaction chromatography (HILIC), we developed a method to characterize the water-absorbing capabilities of twelve different HILIC stationary phases. Adsorption isotherms for non-modified and monomerically functionalized silica phases adhered to a pattern of monolayer formation followed by multilayer adsorption, whereas water uptake on polymerically functionalized silica stationary phases showed the characteristics of formation and swelling of hydrogels. Water accumulation was affected by adding ammonium acetate as buffer electrolyte and by replacing 5% of the acetonitrile with tertiary solvents capable of hydrogen bonding such as methanol or tetrahydrofuran. The relationship between water uptake and retention mechanism was investigated by studying the correlations between retention factors of neutral analytes and the phase ratios of HILIC columns, calculated either from the surface area (adsorption) or the volume of the water layer enriched from the acetonitrile/water eluent (partitioning). These studies made it evident that adsorption and partitioning actually coexist as retention promoters for neutral solutes in the water concentration regime normally encountered in HILIC. Which factors that dominates is dependent on the nature of the solute, the stationary phase, and the eluting conditions.
authors.affiliation: Department of Chemistry, Umeå University, S-90187 Umeå, Sweden; Merck SeQuant AB, S-90719 Umeå, Sweden.
authors.forename: Ngoc Phuoc
authors.initials: NP
authors.lastname: Dinh
authors.forename: Tobias
authors.initials: T
authors.lastname: Jonsson
authors.forename: Knut
authors.initials: K
authors.lastname: Irgum
mesh_terms: D000327:Adsorption; D002021:Buffers; D002853:Chromatography, Liquid / Q000295:instrumentation*; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D002021:Buffers; D014867:Water
keywords: Eluents; HILIC; HPLC; Retention mechanism; Stationary phases