Capillary electrophoresis of inorganic anions in hydro-organic media. Influence of ion-pairing and solvation phenomena.
The capillary electrophoresis separation of four inorganic anions (NO3-, I-, Br- and SCN-) was investigated over the whole range of methanol-water mixture composition. As the separation selectivity was strongly dependent on the solvent composition, the influence of ion-pairing and solvation phenomena was examined in depth in an attempt to explain this modification. First, a series of experiments was performed in methanolic background electrolytes, with counter-ions of different size. Ion-pair formation involving electrolyte ions was assessed to allow for a correction for free electrolyte ion concentration. Ion-pair formation constants between each inorganic anion and electrolyte counter-ion were next determined from the variations of the anion mobility as a function of the free counter-ion concentration. In view of the low values obtained, ion-pair formation alone failed to explain the selectivity variations. Solvation phenomena were then investigated with the help of a theoretical quantum model, the density functional theory (DFT), coupled with a polarizable continuum model to mime non-specific solvent effects. Whereas this model proved successful at predicting the mobility order at infinite dilution in water, it failed to predict the correct order in methanol.
Descroix
Stéphanie
S
Ecole Nationale Supérieure de Chimie de Paris, Laboratoire d'Electrochimie et Chimie Analytique, UMR CNRS 7575, 11 Rue Pierre et Marie Curie, F-75231 Paris Cedex 05, France.
Varenne
Anne
A
Adamo
Carlo
C
Gareil
Pierre
P
D000838:Anions / Q000032:analysis*; D019075:Electrophoresis, Capillary; D012995:Solubility
D000838:Anions