Viscous effects in capillary electrophoresis: theory and experiment

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• Capillary electrophoresis (CE) is a powerful separation technique.
• Viscous additives are sometimes used to modify CE performance.
• Understanding additive effects on resolution is crucial for method optimization.

Purpose of the Study:

• To develop a theory relating viscous additive effects to resolution in CE.
• To identify conditions under which viscous additives improve small molecule separation.
• To investigate the impact of additives on resolution per unit time.

Main Methods:

• Theoretical development of resolution in CE with viscous additives.
• Analysis of electrophoretic and electroosmotic velocity contributions.
• Experimental CE separations using polyethylene glycol (PEG) as an additive with a surfactant mixture.

Main Results:

• Resolution improvement with viscous additives requires solute-additive binding or opposing flow velocities.
• Increased viscosity generally decreases resolution per unit time.
• Specific additive concentrations can enhance resolution for certain peaks while decreasing it for others.
• PEG addition reduced electroosmotic flow, improving resolution for some surfactant components.

Conclusions:

• Viscous additives are not universally beneficial for CE resolution.
• Additive concentration and interactions (binding, flow effects) critically determine separation outcomes.
• Additive adsorption to the capillary wall can significantly impact electroosmotic flow and resolution.