Hydrodynamic injection on electrophoresis microchips using an electronic micropipette

Area of Science:

• Analytical Chemistry
• Microfluidics
• Separation Science

Background:

• Microchip electrophoresis (ME) is a powerful analytical technique, but sample injection methods can impact performance.
• Electrokinetic (EK) injection in ME can be sensitive to buffer concentration, leading to biased results.
• Hydrodynamic (HD) injection offers an alternative but requires precise control.

Purpose of the Study:

• To develop and evaluate an electronic micropipette as a hydrodynamic injector for microchip electrophoresis.
• To compare the performance of this novel HD injection method with traditional EK injection.
• To assess the impact of buffer concentration on injection bias and repeatability.

Main Methods:

• Fabrication of a polydimethylsiloxane (PDMS) microchip with a cross-channel design for sample splitting.
• Coupling an electronic micropipette to the microchip for automated sample dispensing (0.6 µL).
• Optimization of channel width and device configuration for effective hydrodynamic injection.
• Evaluation using a model mixture of high-mobility cationic species (K+, Li+, Na+).

Main Results:

• The electronic micropipette as an HD injector demonstrated superior resolution and injection-to-injection repeatability compared to EK injection.
• Relative standard deviation (RSD) for peak intensities was <5% (n=10), indicating high repeatability.
• HD injection provided an unbiased profile for K+ and Li+ across varying buffer concentrations, unlike EK injection.
• Limits of detection (LDs) for K+, Na+, and Li+ ranged from 18 to 23 µmol L-1.

Conclusions:

• Electronic micropipette-based HD injection is a simple, portable, and effective method for bias-free sample introduction in ME.
• This approach offers improved analytical performance, including better repeatability and reduced buffer dependency.
• The method requires minimal microfabrication, making it accessible for various analytical applications.