Pressure pulse injection: a powerful alternative to electrokinetic sample loading in electrophoresis microchips

Area of Science:

• Analytical Chemistry
• Microfluidics
• Separation Science

Background:

• Classical electrokinetic injection in capillary electrophoresis (CE) can lead to biased sample injection due to electric field variations and differing electrophoretic mobilities.
• Accurate and reproducible sample injection is crucial for reliable CE analysis.

Purpose of the Study:

• To develop and validate a new, simple capillary electrophoresis microsystem utilizing hydrodynamic pressure pulse injection.
• To demonstrate the advantages of pressure pulse injection over traditional electrokinetic methods, focusing on reduced bias and improved control.

Main Methods:

• A microsystem was designed with a flexible membrane on the sample reservoir to generate controlled pressure pulses (0.1-1.0 s).
• Hydrodynamic injection was achieved by mechanically actuating the membrane, creating a pressure pulse to load the sample.
• A model system using fluorescein/calcein in a borate-Tris-hydroxymethylaminoethane (TRIS) buffer was employed for capillary electrophoresis (CE) analysis.

Main Results:

• Pressure pulse injection successfully maintained sample composition, avoiding the bias associated with electrokinetic injection.
• Variable injection plug volumes were achieved by simply adjusting the pressure pulse duration.
• The technique demonstrated very high speed, excellent repeatability, and enhanced sensitivity in separation analysis.

Conclusions:

• Hydrodynamic pressure pulse injection is a simple, effective, and advantageous method for capillary electrophoresis microsystems.
• This technique overcomes the limitations of electrokinetic injection, offering reduced bias and precise control over injection volume.
• The developed microsystem provides a robust platform for high-speed, sensitive, and repeatable CE separations.