ELECTROSTATIC ION CHROMATOGRAPHY USING DILUTE ELECTROLYTES AS ELUENTS- A NEW METHOD FOR SEPARATION OF ANIONS

A new ion chromatographic method with unique separation selectivity an d ultra-high sensitivity for the separation and detection of inorganic anions was developed. The method uses a conventional reversed-phase O DS stationary phase modified with a zwitterionic surfactant and an aqu eous solution containing a small amount of electrolyte as the eluent. The elution order for the anions differed from that achieved by conven tional anion-exchange, with for example, sulfate being eluted before c hloride, and in contrast to the situation when mater was used as mobil e phase, only a single peak was observed for each analyte anion, Addit ion of the electrolyte to a water mobile phase resulted in an initial large increase in analyte retention times, but further increases in el ectrolyte concentration in the mobile phase produced only minor change s in retention time. Use of bicarbonate as the electrolyte anion permi tted a suppressor to be used with conductometric detection. The abilit y to directly analyse samples of high ionic strength permitted the met hod to be applied to the determination of iodide in saline solution us ing direct UV absorbance detection, with a detection limit of 0.7 ppb. Both the positive and negative charges on the immobilised zwitterioni c surfactant on the stationary phase and the ionic components of the e lectrolyte used in the eluent were considered to contribute to the sep aration.