Two chromatographic narrow-bore columns, a novel 2.6 μm particle-packed Kinetex™ C18 core-shell (50×2.1 mm id) and monolithic Chromolith(®) FastGradient RP-18e (50×2 mm id), were evaluated for the analysis of diastereoisomers of the flavonolignans silybin and 23-O-acetylsilybin under isocratic conditions. The main advantages of the core-shell column are markedly higher efficiency (hmin =2.8 versus 5.6 for silybin A) and better peak symmetry. The Kinetex column exhibits only a slight change in the height equivalent of the theoretical plate with a higher linear velocity of the mobile phase. The monolithic column shows notably higher selectivity in terms of selectivity factor (1.21 versus 1.12) in the analysis of critical-pair of diastereoisomers (silybin A and silybin B) and enables shorter run duration (approx. twofold) together with lower backpressure. The resolution power was found to be comparable, but the Kinetex column required a higher pressure of the mobile phase that, together with the higher chance of clogging, can be a disadvantage in the separation of biological samples. Successful baseline separation of silybin diastereoisomers in real pharmaceutical sample on monolithic column was accomplished.

Institute of Microbiology Centre of Biocatalysis and Biotransformation Academy of Sciences of the Czech Republic Prague Czech Republic

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