Analytical Sciences

Investigations into Tie Lines and Solubility Curves on Phase Diagrams in Open-Tubular Capillary Chromatography Using Ternary Mixed-Carrier Solvents

Yusuke TANIGAWA,* Satoshi FUJINAGA,* Masahiko HASHIMOTO,* and Kazuhiko TSUKAGOSHI*,**

*Department of Chemical Engineering and Materials Science, Faculty of Science and Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan
**Tube Radial Distribution Phenomenon Research Center, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan

Open-tubular capillary chromatography using a ternary solvent mixture consisting of a water–hydrophilic–hydrophobic organic solvent as a carrier solution has been developed. When the ternary carrier solution is fed into the capillary tube, the carrier solvents are radially distributed and generate inner and outer phases in the tube. The outer phase functions as a pseudo-stationary phase in chromatography. In this study, investigations proceeded with reference to the tie lines and solubility curves on the phase diagram of the ternary mixed solvents. Model analytes, 1-naphthol and 2,6-naphthalenedisulfonic acid, were separated in this order with ternary water–acetonitrile–ethyl acetate solvent mixtures (organic solvent-rich solutions) that possessed various solvent compositions on the tie lines. In addition, fluorescence photographs of the dyes dissolved in the ternary solvents in the capillary tubes were observed with a fluorescence microscope-CCD camera system. It was found that the separation performance on the chromatograms and the phase formation observed in the fluorescence photographs were related to data provided through the tie lines and solubility curves on the phase diagram. The solvent compositions on the same tie line that gave different volume ratios of upper and lower phases in a vessel influenced the chromatographic separation, or the resolutions of the analytes, and also the inner and outer phase formation in the chromatography.

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