We developed a capillary chromatography system by using an open capillary tube made of fused-silica, polyethylene, or polytetrafluoroethylene, and a water-hydrophilic/hydrophobic organic mixture carrier solution, called tube radial distribution chromatography (TRDC) system. By comparing with chromatograms obtained via the TRDC system, fluorescence photographs and profiles of the fluorescent dyes dissolved in the carrier solvents in capillary tubes were observed under laminar flow conditions. The chromatograms were obtained for a model mixture analyte consisting of 1-naphthol and 2,6-naphthalenedisulfonic acid with the TRDC system, by using a fused-silica capillary tube and a water-acetonitrile-ethyl acetate carrier solution. By altering the carrier flow rates, we examined the fluorescence photographs and profiles of the dyes, perylene and Eosin Y, dissolved in the carrier solvents in the capillary tube by using a fluorescence microscope equipped with a CCD camera. As confirmed by fluorescence observations, the major inner and minor outer phases generated in the capillary tube were based on the tube's radial distribution of the carrier solvents. We designed and manufactured a microreactor incorporating microchannels in which three narrow channels combined to form one wide channel. When the carrier solvents containing the dyes were fed into the channels, the inner and outer phase generations were also observed in the narrow and wide channels, strongly supporting the conclusions concerning the tube radial distribution phenomenon of the solvents.

When ternary mixed solutions of water-hydrophilic/hydrophobic organic solvents are fed into a microspace under laminar flow conditions, the solvent molecules are radially distributed in the microspace. The specific fluidic behavior of the solvents is termed "tube radial distribution phenomenon" (TRDP). In this study, water-acetonitrile-ethyl acetate mixed solutions (3:8:4 volume ratio) containing fluorescent dyes, perylene (0.1 mM) and Eosin Y (1 mM), were fed into fused-silica capillary tubes (75 μm i.d.) for investigating the TRDP with a fluorescence microscope-CCD camera under various analytical conditions. The pressure at the observation point for the fluorescence on the tube was changed by altering the flow rates, capillary total lengths, and capillary effective lengths. The obtained fluorescence images showed that the TRDP in the capillary tube created the inner and outer phases, i.e., the organic solvent-rich major inner and the water-rich minor outer phases in this case, providing the kinetic liquid-liquid interface. The formation of the inner and outer phases in the capillary tube was observed at flow rates of 0.5 -2.0 μL min -1 under the present analytical conditions. We also discuss the specific formation locations of the major and minor solvents.

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We observed chromatographic separation in an open capillary tube with a water–hydrophilic–hydrophobic organic mixture carrier solution. The separation is thought to be based on the tube radial distrubution of aqueous and organic carrier solvents in the capillary tube. In this study, in order to obtain information concerning the solvent distribution, we delivered a carrier solution containing fluorescent dyes into a microchannel (100 µm in width × 40 µm in depth) and monitored the tube radial distribution of the dyes using a fluorescence microscope. When an organic solvent-rich carrier solution (water–acetonitrile–ethyl acetate; 3:8:4 volume ratio) containing perylene and Eosin Y was fed into the channel, perylene and Eosin Y were distributed around the center and near the inner wall of the microchannel, respectively. This observation consists with the specific solvent distribution proposed for the chromatography system.

& A capillary chromatography system that consists of an open capillary tube composed of fused-silica, polyethylene, and poly(tetrafluoroethylene), and a water-hydrophilic=hydrophobic organic mixture carrier solution has been developed. We call this system the tube radial distribution chromatography (TRDC) system. In this study, variance, theoretical plate number, and height equivalent to a theoretical plate for a solute peak in the chromatogram were expressed using theoretical equations derived from the differential equation for the secondary moment of a solute. The relationship between the thickness and diffusion coefficient in the outer phase in the capillary tube in the TRDC system was calculated from theoretical equations using numerical values for the analytical conditions and experimental data. The outer phase that featured the TRDC system had a larger diffusion coefficient and a larger thickness than those of the stationary phase in standard liquid chromatography. We confirmed the separation performance obtained on the basis of the tube radial distribution of the carrier solvents under laminar flow conditions in the TRDC system by considering the inner and outer phase generation in the capillary tube.