Suppressed electrostatic ion chromatography with tetraborate as eluent and its application to the determination of inorganic anions in snow and rainwater

Abstract

Tetraborate is investigated as the eluent ion for suppressed electrostatic ion chromatography (EIC) using a zwitterionic stationary phase. Good separation of a range of inorganic anions (SO42−, Cl−, NO2−, Br−, NO3−, ClO3−, and I−) was obtained, with detection limits for highly conducting ions (SO42−, Cl−, NO2−, Br−, and NO3−) being less than 8·10−8 M, and for weakly conducting anions (ClO3− and I−) being 2.7·10−7 and 5.8·10−7 M, respectively. Calibration curves were linear up to 1.8 mM of each analyte. Retention times were found to increase with increasing eluent concentration and a linear relationship was observed between log k′ and log[Na2B4O7] for all analytes. This behaviour is attributed to the progressive formation of a binary electrical double layer at the surface of the zwitterionic stationary phase. Retention times of analytes could be manipulated by varying the concentration of the eluent. This new suppressed-EIC system was applied to the determination of inorganic anions (SO42−, Cl−, NO3−, NO2−, and Br−) in snow and rainwater samples.