Ion-exclusion chromatography with the direct UV detection of non-absorbing inorganic cations using an anion-exchange conversion column in the iodide-form

An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na+), ammonium (NH4+) and hydrazine (N2H5+) ions was developed by connecting an anion-exchange column in the I−-form after the separation column. For example, NH4+ is converted to a UV-absorbing molecule, NH4I, by the anion-exchange column in the I−-form after the ion-exclusion separation on anion-exchange column in the OH−-form with water eluent. As a result, the direct UV detection of Na+, NH4+ and N2H5+ could be successfully obtained as well as the well-resolved separation. The calibration graphs of the analyte cations detected with UV at 230 nm were linear in the range of 0.001–5.0 mM. The detection limits at S/N = 3 of the cations were below 0.1 μM. This method was applied to real water analysis, the determination of NH4+ in river and rain waters, or that of N2H5+ in boiler water, with the satisfactory results. This could be applied also to low- or non-absorbing anions such as fluoride or hydrogencarbonate ions by the combination of a weakly acidic cation-exchange resin in the H+-form as the separation column and the anion-exchange conversion column.