DIRECT DETERMINATION OF INORGANIC-IONS AT SUB-PPB LEVELS BY ION CHROMATOGRAPHY USING WATER AS A MOBILE-PHASE

Electrostatic ion chromatography (EIC) was used for determination of trace level inorganic ions. EIC is a new method of separating ions based on simultaneous electrostatic attraction and repulsion interactions between analyte ions and fixed positive/negative charges of a stationary phase, having the special advantage of using only water as the mobile phase. Initial results showing two elutions of the same analyte gave new insights into the mechanism of EIC. It suggests that the zwitterionic stationary phase, like a single charged stationary phase, has a Stern layer and a diffuse layer. The first elution is from the diffuse layer, and the second is from the Stern layer. As simpler analysis is facilitated by a single elution, a new species of inorganic salt with a longer elution time was added to the original sample solution in order to release analyte ions from the Stem layer to the diffuse layer. The newly introduced salt is called a sacrifice species. Without preconcentration, inorganic ions at sub-ppb levels were successfully detected by this method.