Electrosmotic mobility and conductivity in columns for capillary electrochromatography

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• Capillary electrochromatography (CEC) columns often feature both packed and open segments, leading to variations in electric field strength and flow velocity.
• Existing methods for CEC data analysis do not fully account for these interface-related changes.

Purpose of the Study:

• To present a framework for evaluating conductivity ratios and interstitial electroosmotic flow (EOF) mobility in duplex CEC columns.
• To establish these parameters as tools for accurate characterization of CEC columns.

Main Methods:

• Experimental measurement of current and EOF in capillary columns packed with diverse stationary phases.
• Development of a framework to calculate conductivity ratios and both apparent and actual EOF mobilities.
• Comparison of apparent EOF mobility with a newly defined actual EOF mobility.

Main Results:

• The conductivity ratio of packed and open segments was determined, aiding in the evaluation of porosity and tortuosity.
• Actual EOF mobility, independent of porosity and tortuosity, was defined and measured.
• Significant differences were observed between apparent and actual EOF mobilities across various columns.

Conclusions:

• The presented framework offers a robust method for characterizing CEC columns.
• Actual EOF mobility is a more reliable parameter than apparent EOF mobility for assessing packing characteristics and surface properties (zeta potential).
• Recommendations are made to adopt actual EOF mobility for superior CEC column characterization.