Simultaneous ion-exclusion chromatography and cation-exchange chromatography of anions and cations in environmental water samples on a weakly acidic cation-exchange resin by elution with pyridine-2,6-dicarboxylic acid

Abstract

A non-suppressed conductivity detection ion chromatographic method using a weakly acidic cation-exchange column (Tosoh TSKgel OApak-A) was developed for the simultaneous separation and determination of common inorganic anions (Cl⁻, NO₃⁻ and SO₄^2-) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). A satisfactory separation of these anions and cations on the weakly acidic cation-exchange column was achieved in 25 min by elution with a mixture of 1.6 mmol L⁻¹ pyridine-2,6-dicarboxylic acid and 8.0 mmol L⁻¹ 18-crown-6 at flow rate of 1.0 mL min⁻¹. On this weakly acidic cation-exchange resin, anions were retained by an ion-exclusion mechanism and cations by a cation-exchange mechanism. The linear range of the peak area calibration curves for all analytes were up to two orders of magnitude. The detection limits calculated at S/N = 3 ranged from 0.25 to 1.9 μmol L⁻¹ for anions and cations. The ion-exclusion chromatography–cation-exchange chromatography method developed in this work was successfully applied to the simultaneous determination of major inorganic anions and cations in rainwater, tap water and snow water samples.