Special Additives in Mobile Phase

The peak shapes of metal chelating analytes are often poor because metal impurities in the stationary phase behave as active sites characterized by slowo desorption kinetics and higher interaction energies compared to reversed phase ligand sites. This phaiomaion is typical of silica-based stationary phases [31] ultrapure silicas were made commercially available to reduce it. However, styrene-divinylbenzene-based chromatogripliic packings suffer from the same problem and it was hypothesized that metals may be present in the matrix at trace conditions because they were used as additives in the polymerization process they may have been c tured via Lewis acid-base interactions between the aromatic ring n electrons and impurities in the mobile phase [32]. 

5 MODIFICATION OF ELUENT IONIC STRENGTH AT CONSTANT IPR CONCENTRATION 

It is a common practice in IPC to buffer the mobile phase at a suitable pH to control analyte ionization and avoid analyte acid-base equilibrium that would be deleterious for peak shape. For a long time, inorganic components of a buffer were considered 

Lower electrostatic surface potential according to Equation 3.5 because the fixed surface charges are better shielded by the IM ions in the electrical double layer this promotes analyte elution via a competition between IM and analyte ions for the adsorbed IPR. 

A Donnan effect that prevents self-repulsion of the similarly charged adsorbed IPR ions at higher ionic strength, the higher surface concentration of the IPR ( LH in Equation 3.5) partially compensates for the decreased magnitude of the electrostatic surface potential due to the increased Scoi in Equation 3.5. 

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