Reducing pH gradients in free-flow electrophoresis

Area of Science:

• Analytical Chemistry
• Separation Science
• Chemical Engineering

Background:

• Small-volume continuous-flow synthesis (CFS) is beneficial for chemical production and research.
• Integrating CFS with continuous purification is highly desirable but limited by purification technique stability.
• Milli free-flow electrophoresis (mFFE) is a promising continuous purification method but suffers from instability due to electrolysis-induced ions.

Purpose of the Study:

• To investigate the severity of pH and conductivity gradients in mFFE.
• To identify conditions causing instability in mFFE.
• To develop strategies to improve mFFE stability for seamless integration with CFS.

Main Methods:

• Experimental demonstration of pH gradient formation under various flow rates and electric field strengths.
• Calculation of optimal hydrodynamic flow rates for ion evacuation at electrodes.
• Design and testing of a prototyped mFFE device with deep channels.

Main Results:

• Detrimental pH gradients were experimentally confirmed in mFFE at flow rates ≤ 8 mL/min and electric fields ≥ 25 V/cm.
• Calculations showed that increased local hydrodynamic flow rates effectively mitigate these gradients.
• A prototyped mFFE device with deep channels demonstrated successful reduction of pH gradients across a wider operating range.

Conclusions:

• Electrolysis-induced ions significantly impact mFFE stability, creating detrimental pH gradients.
• Optimized hydrodynamic flow, facilitated by deep channel design, effectively suppresses these gradients.
• The enhanced mFFE design enables stable continuous purification, suitable for integration with small-volume CFS.