Manipulation of separation selectivity for alkali metals and ammonium in ion-exchange capillary electrochromatography using a suspension of cation exchange particles in the electrolyte as a pseudostationary phase

Abstract

The viability of using ion‐exchange particles as a pseudostationary phase in capillary electrochromatography for the separation of monovalent inorganic cations has been investigated. Using sulfonated polymeric particles (average diameter 225 nm) as the pseudostationary phase, the separation selectivity for alkali metals and ammonium was examined under a range of background electrolyte compositions and employing indirect absorbance detection. Addition of ion‐exchange particles to the background electrolyte resulted in a reduction in the observed electrophoretic mobility of the analytes due to the establishment of ion‐exchange interaction with the pseudostationary phase, with the decrease in mobilities following the ion‐exchange interaction order for these analytes with a sulfonated stationary phase. Increasing the concentration of the particles resulted in a uniform reduction in the electrophoretic mobility of the analytes, similar to that observed in micellar electrokinetic chromatography. Conversely, increasing the concentration of the cationic indirect detection probe (which also acted as an ion‐exchange competing cation) resulted in a decrease in the ion‐exchange interaction with the particles and a reduction of the relative ion‐exchange contribution to the overall separation mechanism. Plots of log[retention factor] versus log[electrolyte concentration] were linear, as is the case for ion‐exchange chromatography, but the observed slopes were greater than predicted from ion‐exchange theory. Indirect absorbance detection was found to give poor sensitivity due to light scattering effects caused by the particles of pseudostationary phase.

Modelling and optimization of the separation of anions in ion chromatography - capillary electrophoresis

“…Ion-exchange (IE) interactions may be introduced into a CE system by using an IE stationary phase packed into a capillary [2±4] or adsorbed onto the capillary wall in open tubular columns [5,6]. However, the column capacity in these methods is a fixed parameter and can only be varied by making another column.…”

Indirect spectrophotometric detection of inorganic anions in ion-exchange capillary electrochromatography

“…These methods operate by incorporation of ion-exchange interactions into a capillary electrophoretic separation. Various methods have been employed to introduce these ion-exchange interactions, including (i) using various pseudostationary phases such as soluble polymers [2±5], dendrimers [6], or microparticles [7]; (ii) using true stationary phases in packed columns [8,9], and (iii) open-tubular (OT) columns in which the stationary phase is attached to the capillary wall ( [4,10]; Breadmore et al, submitted). These methods can all be classified as ion exchange-capillary electrochromatography (IE-CEC) and are attractive because their separation selectivities can be varied between the extremes of CE and IC, so that particular analytical problems can be solved by manipulating the contribution of each method to the final separation.…”

Recent developments in capillary EKC based on carbon nanoparticles

“…Unlike other types of nanoparticles (silica 39, 41, gold 38, 40 and polymers 42, 43), CNPs possess an aromatic system delocalized over their surface, which makes them specially suitable for separating aromatic compounds or substances capable of interacting with aromatic systems. This can be expected to facilitate the development of EKC separations, where direct interaction of the analytes with nanoparticles is essential.…”