DUAL-COLUMN SEPARATION AND DETECTION OF ANIONS IN NON-SUPPRESSED ION CHROMATOGRAPHY

Detector response in ion chromatography is normally given as a function of the difference in ion-equivalent electroconductivity between an analyte ion and a competing ion, since the elution of the analyte ion is accompanied by a decrease in the concentration of the competing ion equivalent to that of the analyte ion. If the elution of analyte ions and the changes in concentration of the competing ion could be monitored separately, chromatographic results would include qualitative information, since the peak area of an analyte ion is not only dependent upon concentration but is also dependent upon ion-equivalency and thus can be used as an identifier. In this study, we tried to resolve peak components into the analyte ion and the competing ion by means of a second column following the analytical column, through which they migrate at different speeds. When a reversed-phase chromatographic column (Asahipak GS-310M) was used as the second column, each anion that was separated on the analytical column {Shim-pack IC-A3, mobile phase, 2.5 mM phthalic acid and 2.4 mM tris(hydroxymethyl)aminomethane} gave two peaks; one positive and the other negative. The areas of the positive peaks were peculiar to the individual anions corresponding to electroconductivities, while the areas of negative peaks were essentially equivalent to analyte concentrations. The anions, therefore, could easily be identified by using the ratios of positive and negative peak-areas along with retention times.