Supercritical fluid chromatography in chiral separations: Evaluation of equivalency of polysaccharide stationary phases

Nine different chiral columns based on covalently immobilized or coated tris(3,5-dimethylphenylcarbamate) cellulose and amylose have been explored. We evaluated their respective enantioselective potential including the enantioseparation and qualitative characteristics of peaks. The generic screening conditions were using gradient elution from 5 to 40% organic modifier/CO2 during 3 min with about 40 enantiomer pairs. Primary screening was carried out using ten different mobile phases varying in type of additives while using one representative amylose- and one cellulose-based column. The complete evaluation of all nine columns was then carried out using three best performing organic modifiers: (1) methanol + 0.1% trifluoroacetic acid + 0.1% diethylamine, (2) isopropanol + 0.1% trifluoroacetic acid + 0.1% diethylamine, and (3) methanol + 0.1% ammonium hydroxide. Equivalency of different columns with the same chiral selector was not confirmed. Columns with the same stationary phase but different supports or manufacturing methods displayed differences in enantioselectivity and general performance. The similarity corresponded to 62 and 63% for the three cellulose-coated columns taking CEL1 as the reference. The similarity was 67% for the pair of amylose-based coated columns. For immobilized columns, the similarity was 69 and 59% for celluloses and amyloses pairs, respectively. The best performing column based on success rate of enantioseparation was Chiralcel OD-3 when using methanol + 0.1% trifluoroacetic acid and 0.1% diethylamine combined additive.