Mass transfer in rectangular chromatographic channels

Area of Science:

• Analytical Chemistry
• Separation Science
• Microfluidics

Background:

• Rectangular channels are increasingly used in microfluidic separations.
• Existing plate height equations by Giddings and Golay primarily address infinite or specific finite channel widths and unretained analytes.
• Modifications are needed for retained analytes and electroosmotic flow in finite rectangular channels.

Purpose of the Study:

• To develop and present modified plate height equations for rectangular channels.
• To investigate the impact of finite channel width on chromatographic and electrophoretic separations.
• To account for electroosmotic flow profiles in plate height calculations.

Main Methods:

• Numerical Fourier transform approach was employed.
• Plate height contributions from mobile phase mass transfer were analyzed.
• Results were compared to the established Golay equation for cylindrical systems.

Main Results:

• New expressions for plate height (H) were derived, incorporating channel width-to-height ratio (phi).
• The finite channel width significantly increases plate height for unretained solutes (up to eightfold).
• The effect of finite width on retained solutes is generally minor, with retention factor (k') playing a key role.

Conclusions:

• The study provides essential equations for optimizing rectangular channel-based separations.
• Finite channel width effects are substantial for unretained analytes, necessitating adjustments to theoretical models.
• The findings are applicable to various channel coatings and flow conditions, including electroosmotic flow.