Electrokinetic injection for stacking neutral analytes in capillary and microchip electrophoresis

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• On-column stacking enhances signal detection in capillary electrokinetic chromatography by narrowing analyte peaks.
• Traditional methods often use low-pressure injections for neutral analytes, which can be time-consuming.

Purpose of the Study:

• To present an on-column mechanism for electrokinetic injection of long sample plugs with simultaneous stacking of neutral analytes.
• To demonstrate faster injection times and improved reproducibility compared to pressure injections.

Main Methods:

• Utilizing an electric field for electrokinetic injection directly into the capillary.
• Implementing simultaneous on-column stacking initiated at the capillary inlet.
• Demonstrating the method with both discontinuous and continuous sample electrolytes.
• Applying the technique to microchip electrokinetic injection using a cross-T channel.

Main Results:

• Electrokinetic injection achieved up to 10x faster injection of neutral analytes compared to pressure injections.
• Analysis times were markedly improved in terms of reproducibility.
• A 10-fold or greater decrease in analysis times was observed with smaller inner diameter capillaries (≤50 µm).

Conclusions:

• Electrokinetic injection with simultaneous stacking offers a significant advancement for capillary electrokinetic chromatography.
• The method provides comparable peak height and area reproducibility to pressure injection.
• This technique is potentially exportable to other electrokinetic methods and capillary array systems.