High efficiency functionalized hydrophilic cyclofructans as stationary phases in sub/supercritical fluid chromatography

Abstract

Packed column SFC has become very popular for preparative and analytical separations due to the low cost of CO2, its accessible critical temperature, and pressure, with the additional benefit of a low environmental burden. Currently, there is a shortage of new polar stationary phase chemistries for SFC. In this work, two new functionalized cyclofructan columns are introduced and evaluated for their performance in achiral SFC separations for the first time. Cyclofructan (CF6), a macrocyclic oligosaccharide, was covalently linked with benzoic acid (BCF6) and propyl sulfonic acid (SCF6) groups by ether bonds. Superficially porous particles (2.7 μm) bonded with modified CF6 showed markedly different selectivity than native CF6. In SFC, peak shapes of amines and basic compounds are often compromised. We show that small quantities (~5.7% v/v) of water added to the methanol modifier in CO2 improves peak symmetries of primary, secondary, and tertiary amines. Efficiencies as high as 200,000 plates/m (reduced plate height ~ 1.8) were observed for benzamide and amitriptyline on the BCF6 column. The relative standard deviations (RSDs) of retention times on BCF6 were about 1.4%, and on SCF6 were less than 1%. Amines on the SCF6 column showed plate counts as high as 170,000 plates/m. Tetramethylammonium acetate is examined as an alternative to water in MeOH. A run time of 36 min with methanol, trifluoroacetic acid, triethylamine mobile phase was reduced to <5 min with complete baseline resolution for a set of amines. The new stationary phases allow greener approaches towards solving separation problems.