Electrochemically modulated liquid chromatography and the Gibbs adsorption equation

Area of Science:

• Analytical Chemistry
• Electrochemistry
• Physical Chemistry

Background:

• Electrochemically modulated liquid chromatography (EMLC) utilizes conductive stationary phases as electrodes.
• This technique allows for the manipulation of chromatographic separations via applied potential (E(app)).
• EMLC provides a novel approach for investigating electrosorption phenomena at electrode-fluid interfaces.

Purpose of the Study:

• To develop and validate EMLC as a tool for examining electrosorption processes.
• To investigate the retention behavior of charged aromatic compounds on porous graphitic carbon (PGC).
• To determine interfacial thermodynamic parameters using chromatographic data.

Main Methods:

• Employing porous graphitic carbon (PGC) as both the stationary phase and working electrode.
• Monitoring the retention factor (k') of charged aromatic compounds as a function of applied potential (E(app)).
• Applying Gibbs adsorption and Lippmann equations to calculate interfacial excess (Gamma), interfacial tension (dgamma), electrode charge (q(M)), and potential of zero charge (PZC).

Main Results:

• Successful determination of interfacial excesses, interfacial tension changes, electrode charge, and PZC for charged aromatic compounds.
• PZC values were accurately determined from plots of ln k' versus E(app).
• Observed shifts in PZC to more cathodic values correlated with increased anion specific adsorption and electrolyte concentration.

Conclusions:

• EMLC is a powerful chromatographic technique for probing electrosorption mechanisms at electrified carbon electrodes.
• The study provides fundamental insights into solute adsorption governed by electrode potential and electrolyte composition.
• The EMLC strategy can be extended to study electrified interfaces under varying mobile-phase conditions, temperature, and pressure.