Effect of the water content on the retention and enantioselectivity of albendazole and fenbendazole sulfoxides using amylose-based chiral stationary phases in organic–aqueous conditions

Four commercially available immobilized amylose-derived CSPs (Chiralpak IA-3, Chiralpak ID-3, Chiralpak IE-3 and Chiralpak IF-3) were used in the HPLC analysis of the chiral sulfoxides albendazole (ABZ-SO) and fenbendazole (FBZ-SO) and their in vivo sulfide precursor (ABZ and FBZ) and sulfone metabolite (ABZ-SO2 and FBZ-SO2) under organic–aqueous mode. U-shape retention maps, established by varying the water content in the acetonitrile- and ethanol–water mobile phases, were indicative of two retention mechanisms operating on the same CSP. The dual retention behavior of polysaccharide-based CSPs was exploited to design greener enantioselective and chemoselective separations in a short time frame. The enantiomers of ABZ-SO and FBZ-SO were baseline resolved with water-rich mobile phases (with the main component usually being 50–65% water in acetonitrile) on the IF-3 CSP and ethanol–water 100:5 mixture on the IA-3 and IE-3 CSPs. A simultaneous separation of ABZ (or FBZ), enantiomers of the corresponding sulfoxide and sulfone was achieved on the IA-3 using ethanol–water 100:60 (acetonitrile–water 100:100 for FBZ) as a mobile phase.