Evaluation of the properties of a superficially porous silica stationary phase in hydrophilic interaction chromatography

The sample capacity, column efficiency (and its variation with flow) of a superficially porous unbonded silica phase (Halo) was investigated using hydrophilic interaction chromatography (HILIC), particularly for separation of basic compounds. Sample capacity compared with totally porous silica phases was somewhat reduced, broadly in line with the decreased surface area, but still favourable compared with reversed-phase separations of these solutes. Efficiencies in excess of 100,000 plates were obtained at room temperature in reasonable analysis times by using a 45 cm coupled column, while generating back pressures compatible with conventional HPLC. Shorter columns offered the possibility of fast analysis of bases, and the unfavourable mass transfer properties reported by others at high flow rate for similar reversed-phase columns, were not apparent. While excellent peak shapes were obtained for many bases on silica HILIC phases, problems may still occur for some solutes.