Micro-flow injection analysis system: on-chip sample preconcentration, injection and delivery using coupled...

Area of Science:

• Analytical Chemistry
• Microfluidics
• Electrokinetics

Background:

• Microfluidic devices offer miniaturized platforms for chemical analysis.
• Electroosmotic pumps (EOPs) are crucial for fluid manipulation in microfluidic systems.
• Efficient sample preconcentration and injection are vital for sensitive micro-flow injection analysis (FIA).

Purpose of the Study:

• To develop and characterize a microfluidic chip integrating monolithic electroosmotic pumps for sample preconcentration, injection, and delivery.
• To demonstrate quantitative control over low nano-litre sample volumes using electrokinetic injection.
• To showcase a novel on-chip cation preconcentration and elution method using a modified EOP.

Main Methods:

• Fabrication of a microfluidic chip with two monolithic electroosmotic pumps.
• Utilized electrokinetic (EK) injection controlled by voltage and time for nano-litre volumes.
• Employed a nano-flow sensor (NFS) for real-time flow rate monitoring.
• Integrated a capacitively coupled contactless conductivity detector (C(4)D) for detection.
• Modified an EOP with an anionic surfactant for on-chip cation preconcentration.

Main Results:

• Monolithic EOPs achieved stable, bubble-free flow rates at <2 kV and <10 microA.
• EK sample injection provided quantitative control down to nano-litre volumes.
• NFS demonstrated rapid response times (<5-10 s) to voltage changes.
• The integrated system successfully performed micro-flow injection analysis.
• On-chip cation preconcentration and elution were successfully demonstrated.

Conclusions:

• The developed microfluidic chip with integrated EOPs provides precise control over sample handling for FIA.
• The system is capable of sensitive analysis through controlled injection and on-chip preconcentration.
• This work advances microfluidic technology for miniaturized analytical systems.