Capillary chromatography based on tube radial distribution of aqueous‐organic mixture carrier solvents: Introduction of inner‐wall‐modified capillary tubes

Abstract

We developed a novel capillary chromatography using an open capillary tube and a water-hydrophilic/hydrophobic organic solvent mixture as a carrier solution. The capillary chromatography was called a tube radial distribution chromatography (TRDC) system. In this study we tried to introduce inner-wall-modified (e.g. phenylboronic-acid- and iminodiacetic-acid-modified) fused-silica capillary tubes to the TRDC system to separate model mixture analytes. The phenylboronic-acid-modified capillary tube was combined with absorption detection to analyze a mixture of adenosine and deoxyadenosine. The iminodiacetic-acid-modified capillary tube was combined with chemiluminescence detection using a luminol reaction to analyze a mixture of copper(II) and hematin. A water (carbonate buffer)/ACN/ethyl acetate (2:7:4 v/v/v) and a water (carbonate buffer)/ACN/ethyl acetate (15:3:2 v/v/v) mixture solution were used as carrier solutions in the TRDC system, and typical carbonate buffer solutions not containing any organic solvents were also used as carrier solutions as reference solutions. In both modified capillary tubes, the organic-solvent-rich carrier solution successfully improved the separation of the mixture analytes in the system, and the water-rich carrier solution greatly depressed their separation, when compared with chromatography using carbonate buffer carrier solutions containing no organic solvents. Such observed phenomena were discussed considering the separation mechanism of the TRDC system.