Determination of Inorganic Anions by Electrostatic Ion Chromatography With a Cation Exchange Column as a Pre-Column for Conversion of the Cations Into a Common Species

The problem of “multiple” distribution of the analyte ions encountered in the separation of inorganic ions by electrostatic ion chromatography (EIC) was overcome. EIC is a new type of ion chromatography (IC) where zwitterionic molecules are used as the stationary phase and pure water serves as the mobile phase. Both ions and polar organic compounds can be separated by EIC and the simultaneous electrostatic attraction-repulsion interactions between the positive-negative charges (or polarities) of the analytes and the stationary phase are considered to be the main mechanisms for the separation. In the analysis of inorganic ions by EIC, each species of the cation and/or anion was distributed to all species of the counterion and co-eluted as pairing ions. To avoid such “multiple” distribution of the analyte ions, the analyte cations were converted into a common species of either Na+ or Mg2+ by using conventional cation exchange columns as the pre-column. The analyte anions were excellently separated by this method and, furthermore, “exclusive” distribution (single peak per one species of anion) was obtained. Real sample (underground water) was analyzed in duplicate using a conventional anion-exchange IC and this proposed method and identical results were obtained.