Changes in Retention and Detector Response for Weak Acid Anions as a Function of Mobile Phase pH in Indirect Photometric Chromatography with a Singly Charged Eluent Ion

Abstract

Indirect photometric chromatography (IPC) involves analyte separation by ion exchange and detection using indirect UV photometry. Since retention and detection are impacted by the speciation of the weak acid analytes and eluents, both are influenced by mobile phase pH. In this study, the retention and detection characteristics of several weak and strong acids were studied as a function of mobile phase pH with an eluent whose speciation was only marginally impacted by pH. In so doing, analyte ion effects are divorced from the eluent ion effects which are typically observed with the weak acid eluents used in IPC. Trends in both the detection and retention characteristics of the weak acids mirrored their changing speciation and could be used to estimate their acid dissociation constants.