Interference of some matrix ions in cation-exchange chromatography

Ion chromatographic analysis of ions in samples containing complex matrix composition strongly depends on the on-column co-processes caused by sample matrix components. In the present publication studies of different separation phenomena in cation-exchange chromatography are described. The studies were performed at ‘non-linear’ chromatographic conditions, when the concentration of matrix (interfering) ions significantly exceeded the concentration of the eluent ions. During the research work, the processes already identified in anion-exchange chromatography, i.e. self-elution, on-column change of the eluent and sample-induced micro-gradient elution were used to explain the chromatographic behavior of alkaline and earth-alkaline cations when samples with high matrix cation concentration were analyzed. When present at higher concentrations, the ammonium cation was found to cause self-elution (NH4+ fraction) as well as on-column eluent neutralization due to its ability to diffuse into/back from the porous core of the stationary phase (NH3 fraction). Co-elution of a matrix component and analytes of interest caused spectroscopic interferences that additionally influenced the peak shape of each individual analyte.