Simultaneous separation of inorganic cations and anions by ion chromatography using a single column coated with weak/strong-charged zwitterionic bile salt micelles.

A single reversed-phase ODS (octadecyl silica) column coated with taurine-conjugated bile salt micelles has been investigated for simultaneous separation of inorganic cations and anions. Under acidic conditions in the separation column, taurine-conjugated bile salts are protonated; therefore, the stationary phase coated with taurine-conjugated bile micelles exists as a "weak/strong"-charged zwitterionic stationary phase (H+ and SO3-). The weak/strong-charged zwitterionic stationary phase provides a new retention mechanism which is different from conventional ion chromatography in that both positive and negative charges are close together in a single molecule, resulting in simultaneous electrostatic attraction and repulsion of the analyte ions. Also, the stronger negative charge (sulfonate) of the stationary phase works as a cation-exchange site at the same time. The combined effects of cation-exchange and simultaneous electrostatic repulsion/attraction interactions were successfully used in ion chromatography for the simultaneous separation of inorganic cations and anions.