Capillary Chromatography Using an Annular and Sluggish Flow in the Ternary Water–Acetonitrile–Ethyl Acetate System as Carrier Solution

Abstract

Abstract An open-tubular capillary chromatography system was developed using an annular and sluggish flow system in a ternary water–acetonitrile–ethyl acetate mixed solvent as carrier solution. Fused-silica capillary tubes with different inner diameters of 75 and 200 µm were used. The smaller tube was inserted into the larger tube using a T-type joint. Water–acetonitrile and acetonitrile–ethyl acetate mixed solutions were delivered to the smaller and larger tubes, respectively, and then combined at the other end of the smaller tube located in the larger tube, generating annular and sluggish flows in the water–acetonitrile–ethyl acetate ternary mixed solution (2:5:3 and 2:4:3 (v/v/v), respectively). The annular flow comprised the organic solvent-rich inner and water-rich outer phases and the sluggish flow comprised the organic solvent-rich sluggish domain and water-rich continuous phases. A model analyte mixed solution of 1-naphthol (hydrophobic) and 2,6-naphthalenedisulfonic acid (hydrophilic) were injected into the smaller tube and proceeded to the annular or sluggish flow in the larger tube, where they were separated and detected in that order. As observed, the annular and sluggish flows in the microspace could be used for separation without any specific treatments such as tube packing or coating.