Cyclodextrin‐modified monolithic columns for resolving dansyl amino acid enantiomers and positional isomers by capillary electrochromatography

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Abstract
We describe β- and γ-cyclodextrins (β- and γ-CD)-modified monolithic columns prepared by sol-gel process and chemical modifications. The monolithic silica column was fabricated inside a fused-silica capillary with 100 μm inner diameter by sol-gel process. The monolithic silica matrix was chemically modified chiral selectors of β- or γ-CDs with a spacer of 3-glycidoxypropyltrimethoxysilane by on-column reactions. γ-CD-modified monolithic column has successfully been applied for the separation of dansyl amino acid enantiomers. β-CD-modified monolithic column has been used for the separation of the positional isomers of o-, m-, and p-cresols and the enantioseparation of racemates of benzoin and several dansyl amino acids by capillary electrochromatography, respectively. For the separation of neutral positional isomers, a positive electric field was applied. However, for the separation of negatively charged analytes, a negative electric field was applied at the inlet of column. The separation efficiency of 5.0×104 theoretical plates/m for dansyl-L-threonine was obtained at electric field strength of −300 V/cm in the mobile phase of 50 mM 2-(N-morpholino)ethanesulfonic acid (MES)-Tris/methanol (70/30) buffer at pH 7.0. L-Enantiomers were eluted as the first peak. Scanning electron micrograph showed that monolithic columns have the morphology of continuous skeleton and large through-pores.

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