Successive non-suppressed ion chromatography of common cations and anions using dual columns with single eluent

Abstract

A successive non-suppressed ion chromatography (IC) system for the determination of common cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) and anions (Cl⁻, Br⁻, NO₃⁻, SO₄²⁻) was developed, using two separation columns and a single eluent. 5-Sulfoisophthalic acid eluent was very suitable for such separations with a commercially available cation-exchange column for the mono- and di-valent cations and with an ODS column coated with cetyltrimethylammonium for the anions. Both cations and anions were detected with conductimetrically high sensitivity without any suppressor. After injecting an aliquot of sample solution, the solvent front from the cation-exchange column, including most of the anionic species, was firstly accumulated into the additional 2 ml accumulation loop for 60 s, while the cation IC was performed. Subsequently, the accumulated fraction was introduced into the anion-exchange column and chromatographed. Relative standard deviations (RSDs) of retention times and conductimetric area responses for common cations were within 6% and within 4%, respectively. The linear relationships between molar concentration and detector response ranged from 0.01 to 1.00 mM with r² of 0.9994 for Na⁺, 0.9992 for K⁺, 0.9993 for Mg²⁺, and 0.9988 for Ca²⁺. The successive anion IC through the accumulating process was also quantitative, with 95% recovery or over for each analyte. The linear ranges were between 0.01 and 1.00 mM with r² of 0.9996 for Cl⁻, 0.9997 for Br⁻, 0.9993 for NO₃⁻, and 0.9984 for SO₄²⁻. The method was applied to the determination of common cations and anions in several mineral waters and a hot spring water.