Factors Affecting the Resolution and Detectability of Inorganic Anions by Non-Suppressed Ion Chromatography

Abstract

The three phthalic acid isomers were investigated as eluents for non-suppressed ion chromatography. Using a specially designed conductivity detector in conjuction with conventional HPLC instrumentation, very sharp separation of anions was achieved. Since the eluent anions compete with the sample anions during the chromatographic process, changes to eluent species, concentration, and/or pH greatly affect the detection and resolution of the sample anions. Decreasing concentration and pH greatly incease retention time, thus degrading peak shape and symmetry. The sensivity observed for Cl^- (0.25 ppm) and NO₃^- (0.50 ppm) is comparable to conventional suppressed ion chromatography, while that for SO₄^-2 (1.25 ppm) is only slightly less. Isophthalic acid provides better resolution and selectivity that o-phthalic acid. It can be used at a lower concentration, thus also providing better detection limits and lower background conductivity.