Extended thermodynamic approach to ion interaction chromatography. Influence of the chain length of the solute ion: a chromatographic method for the determination of ion-pairing constants

Abstract

The influence of the chain length in Ion Interaction Chromatography (IIC), previously named Ion Pair Chromatography, was investigated. The system examined is a C18 stationary phase and a variable, salt-controlled, mixture of a phosphate buffer pH 2.1 in methanol containing tetrabutylammonium bromide as Ion Interaction Reagent. IIC proves to be a good alternative to the well established spectrophotometric and conductometric methods of obtaining thermodynamic ion-pairing constants. The latter increase with increasing analyte chain length and decrease with increasing methanol concentration in the eluent: both results support a physical chemical description of the hydrophobic ion-pairing process at variance with the classical, Bjerrum-type modelling of the purely electrostatic interaction between inorganic ions. The calculated deltaG(o) are reliable because they compare to non-chromatographic estimates of deltaG(o) for similar systems. The present extended thermodynamic approach is able to predict and explain why the purely electrostatic approach works better for lower analyte lipophilicity or higher organic modifier concentration.

Preparation and characterization of monoliths covalently bonded chelating groups for capillary electrochromatographic separation of metal ions

“…The metal ions were precomplexed by the polydentate ligand EDTA. For the separation of negatively charged species in a reversed-phase column, TBAB is a good choice as an ion-pair reagent because it is univalent, aprotic, soluble and does not undergo aggregation or secondary equilibria [27,28]. In this work, the monolith was supposed to have some properties of a reversedphase column.…”

Retention study of some cation‐type compounds using bile acid sodium salts as ion pairing agents in liquid chromatography

“…Since that time, applications of the ion‐pairing mechanism have grown substantially. A great number of ion‐pairing agents have been used in applications (Skelly, 2003), and several models have been proposed to describe the retention mechanism in ion‐pair chromatography including the partition model (David et al ., 2005) and surface adsorption double layer model (Bartha and Stahlberg, 1994; Cecchi, 2005).…”