Enantioseparation of chiral sulfonates by liquid chromatography and subcritical fluid chromatography

Tert-butylcarbamoyl-quinine and -quinidine weak anion-exchange chiral stationary phases (Chiralpak (R) QN-AX and QD-AX) have been applied for the separation of sodium beta-ketosulfonates, such as sodium chalconesulfonates and derivatives thereof. The influence of type and amount of co- and counterions on retention and enantioresolution was investigated using polar organic mobile phases. Both columns exhibited remarkable enantiodiscrimination properties for the investigated test solutes, in which the quinidine-based column showed better enantioselectivity and slightly stronger retention for all analytes compared to the quinine-derived chiral stationary phase. With an optimized mobile phase (MeOH, 50 mM HOAc, 25 mM NH3), 12 of 13 chiral sulfonates could be baseline separated within 8 min using the quinidine-derivatized column. Furthermore, subcritical fluid chromatography (SubFC) mode with a CO2-based mobile phase using a buffered methanolic modifier was compared to HPLC. Generally, SubFC exhibited slightly inferior enantioselectivities and lower elution power but also provided unique baseline resolution for one compound.