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

Abstract

An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na +), ammonium (NH 4 +) and hydrazine (N 2H 5 +) ions was developed by connecting an anion-exchange column in the I −-form after the separation column. For example, NH 4 + is converted to a UV-absorbing molecule, NH 4I, 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 +, NH 4 + and N 2H 5 + 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 NH 4 + in river and rain waters, or that of N 2H 5 + 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.