Tube radial distribution chromatography system developed by combining commercially available HPLC system and open-tubular capillary tube as separation column

Tube radial distribution chromatography based on tube radial distribution flow, or annular flow, in an open-tubular capillary has been reported, where the annular flow is created through phase separation multiphase flow. The chromatographic system requires some specific instruments and treatments for microfluidic flow in the capillary tube. In this study, we developed a new set-up for tube radial distribution chromatography by combining a commercially available HPLC system with an open-tubular capillary tube (with an inner diameter of 100 µm) as a separation column instead of a conventional packed column. The analyte solution was injected with an injection valve (2 μL volume) and a ternary solution of water/acetonitrile/ethyl acetate (3:8:2 vol ratio) was delivered as the eluent to the capillary tube at a flow rate of 8.6 μL min−1. The chromatographic system, that is, the HPLC system equipped with the open-tubular capillary tube, could successfully separate the model analytes, 1-naphthol, 1-naphthalenesulfonic acid, and 2,6-naphthalenedisulfonic acid, with base-line separation. The inner and outer phases in the annular flow worked as the mobile and pseudo-stationary phases, respectively, in the tube radial distribution chromatography system. The experimentally obtained elution times of the analytes were compared with their corresponding theoretical values calculated using their capacity factors for the inner and outer phases and the linear flow velocities of the respective phases.