Gradient elution in capillary electrochromatography

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• High-performance liquid chromatography utilizes pressure-driven gradients for enhanced separations.
• Capillary electrochromatography (CEC) traditionally relies on isocratic conditions, limiting its separation power.
• Developing gradient elution for CEC is crucial for improving analytical performance.

Purpose of the Study:

• To develop and demonstrate a novel system for electroosmotically driven solvent gradients in CEC.
• To adapt gradient elution principles from HPLC to the unique electroosmotic flow regime of CEC.
• To validate the system's capability in separating complex mixtures.

Main Methods:

• A system was engineered to merge two electroosmotic flows, regulated by computer-controlled voltages.
• Fused-silica capillary arms delivered distinct mobile phases to a T-connector, mixing before entering the packed column.
• High-voltage power supplies controlled electroosmotic flow rates, creating dynamic solvent gradients.
• The capillary column was electrokinetically packed with 3-μm reversed-phase particles.

Main Results:

• Dynamic gradients with submicroliter per minute flow rates were successfully generated.
• Mobile phase composition was confirmed to change in response to programmed voltage profiles.
• A mixture of 16 polycyclic aromatic hydrocarbons was separated in under 90 minutes.
• The system demonstrated effective gradient elution in CEC.

Conclusions:

• The developed system provides a robust method for generating electroosmotically driven solvent gradients in CEC.
• This technique offers a powerful alternative to traditional isocratic methods, enhancing separation efficiency.
• The approach is adaptable for generating other gradient types, including pH and ionic strength, in capillary electrokinetic separations.