Very high-pressure capillary liquid chromatography assisted by voltage

Area of Science:

• Analytical Chemistry
• Separation Science
• Chromatography

Background:

• Capillary liquid chromatography and capillary electrochromatography (CEC) are advanced separation techniques.
• Driving mobile phase through capillary columns packed with small particles requires optimized conditions.
• Understanding the interplay of pressure and voltage is crucial for efficient separations.

Purpose of the Study:

• To combine capillary liquid chromatography and CEC for enhanced mobile phase control.
• To investigate the effects of pressure and voltage on linear velocity and separation efficiency.
• To analyze retention factor behavior under combined pressure-voltage conditions.

Main Methods:

• Utilized capillary columns packed with 1.5 microm nonporous particles.
• Employed a combination of high inlet pressures (up to 690 bar/10,000 psi) and applied voltages (up to 25 kV).
• Measured linear velocities and separation efficiencies under varying pressure-voltage conditions.

Main Results:

• Achieved linear velocities near 3 mm/s with high pressure and voltage.
• Identified an optimal pressure-voltage combination (350 bar/5000 psi and 5 kV) for maximum linear velocity.
• Observed separation efficiencies consistent with van Deemter equation predictions at near-optimal velocities.
• Noted a decrease in retention factors with increasing voltage, attributed to Joule heating.

Conclusions:

• The combination of capillary liquid chromatography and CEC effectively drives mobile phase through packed columns.
• Joule heating significantly influences retention behavior in pressure-voltage driven CEC.
• This hybrid approach offers high separation efficiencies relevant to liquid chromatography theory.