Peak Distortion Effects in Analytical Ion Chromatography

Abstract

The elution profile of chromatographic peaks provides fundamental understanding of the processes that occur in the mobile phase and the stationary phase. Major advances have been made in the column chemistry and suppressor technology in ion chromatography (IC) to handle a variety of sample matrices and ions. However, if the samples contain high concentrations of matrix ions, the overloaded peak elution profile is distorted. Consequently, the trace peaks shift their positions in the chromatogram in a manner that depends on the peak shape of the overloading analyte. In this work, the peak shapes in IC are examined from a fundamental perspective. Three commercial IC columns AS16, AS18, and AS23 were studied with borate, hydroxide and carbonate as suppressible eluents. Monovalent ions (chloride, bromide, and nitrate) are used as model analytes under analytical (0.1 mM) to overload conditions (10-500 mM). Both peak fronting and tailing are observed. On the basis of competitive Langmuir isotherms, if the eluent anion is more strongly retained than the analyte ion on an ion exchanger, the analyte peak is fronting. If the eluent is more weakly retained on the stationary phase, the analyte peak always tails under overload conditions regardless of the stationary phase capacity. If the charge of the analyte and eluent anions are different (e.g., Br(-) vs CO3(2-)), the analyte peak shapes depend on the eluent concentration in a more complex pattern. It was shown that there are interesting similarities with peak distortions due to strongly retained mobile phase components in other modes of liquid chromatography.

The utility of statistical moments in chromatography using trapezoidal and Simpson's rules of peak integration

“…Similarly competitive isotherms may also lead to fronting and unique peak shapes. Such peak shapes were reported for ion chromatography . Injecting large enough mass of solute on the column may cause a part of the solute to travel ahead of the main band and emerge as a breakthrough, giving rise to a fronting peak profile.…”

Growth and Nitrate Uptake in Nannochloropsis gaditana and Tetraselmis chuii Cultures Grown in Sequential Batch Reactors

“…High concentrations of chloride ions are known to interfere with ion chromatographic systems, overloading the detectors. This overload causes peak distortions and poor component separation (Wahab et al, 2014). One solution to this problem is to dilute samples to mitigate concentration overload.…”

Effect of injection matrix concentration on peak shape and separation efficiency in ion chromatography

“…Recent studies [41] have shown that mass overload of analyte on modern ion chromatography columns obeys a competitive Langmiur isotherm behavior, in which both analytes and strongly adsorbed mobile phase components compete for sorption sites [38,42]. For Langmuir isotherms, the competitive situation is described by:…”