Visual representation of Ion Exchange Separation, Bridge Ion Separation Technology (BIST™), and other possible ion interactions in a charged HPLC column.
1) Ion Exchange Separation (Single-Charged Ions in an Aqueous MP): The surface has a net-positive charge, and retains the single-charged negative ions. The glow around the ions represents the solvation layer that forms around the charged particles in this aqueous solution. This solvation layer minimizes interactions between the ions in solution. Title: Ion Exchange Separation, BIST ™, and other Ionic Interactions in Different Solutions with a Charged Surface in an HPLC Column
2) Doubly-Charged Ions in an Aqueous MP These conditions are nearly identical to those for Ion Exchange Separation. The surface still has a net-positive charge and retains the doubly-charged negative ions. The aqueous mobile phase still minimizes the interactions between the ions with the solvation layer that forms around the charged ions. The positively-charged analyte, represented by the larger gradient ion, is not retained.
3) Single-Charged Ions in a High-Organic MP The conditions have now changed significantly. Since the solution is no longer aqueous, no solvation layer forms around the ions, so the ions are able to interact and form tight-bonded pairs in both solution and on the surface. This pairing transforms the surface charge from net-positive to net-neutral. The positively-charged analyte, represented by the larger gradient ion, is not retained.
4) BIST™ (Doubly-Charged in a High Organic MP) The doubly-charged modifier ions have been introduced to the highly organic mobile phase. Since the solution is not aqueous, the doubly-charged modifier ions pair with the surface, generating a net-negative charge. This allows for the positively-charged analytes to be retained.
