Separation of dansyl-dl-amino acids by open tubular capillary chromatography based on tube radial distribution phenomenon of the ternary mixed carrier solvents

Abstract

Separation of enantiomers, dansyl-DL-amino acids, was carried out by open-tubular capillary chromatography based on the tube radial distribution of the carrier solvents. An untreated poly(tetrafluoroethylene) capillary tube (100 μm inner diameter and 90 cm effective length) as a separation column and a water–acetonitrile–ethyl acetate mixture containing cyclodextrin as a carrier solution were used in the chromatography. An analyte solution of dansyl-DL-amino acids, such as dansyl-DL-methionine, was injected into the capillary tube by a gravity method. The analyte solution was subsequently delivered through the capillary tube with the carrier solution by a microsyringe pump. The ternary mixed carrier solution (water-rich carrier solution) was radially distributed in the capillary tube based on the tube radial distribution phenomenon, causing the formation of inner (water-rich) and outer (organic solvent-rich) phases. The outer or capillary wall phase acted as a pseudo-stationary phase in the chromatography. The analytes were separated through the capillary tube with on-capillary detection by an absorption or a fluorescence detector. The D-enantiomer and the L-enantiomer were eluted in this order with a baseline separation. The separation mechanism of the enantiomers in the open-tubular capillary using cyclodextrin was discussed.