Electroosmotically driven solution mixing in borosilicate theta glass nESI emitters.

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Mass Spectrometry

Background:

• Borosilicate theta glass capillaries are used as nanoelectrospray ionization (nESI) emitters for in-line solution mixing.
• Previous methods were limited to sub-millisecond mixing timescales due to analyte residence time in the Taylor cone.
• Extending mixing timescales is crucial for controlling pre-analysis sample manipulations.

Purpose of the Study:

• To extend solution mixing timescales to the milliseconds regime using electroosmosis in theta tips.
• To demonstrate control over sample properties, such as protein denaturation, prior to mass spectrometry.
• To improve mixing efficiency through induced turbulence.

Main Methods:

• Applied a potential difference between electrodes in theta tip channels to induce electroosmotic flow.
• Utilized fluorescence microscopy with tracer dyes to confirm electroosmosis-driven solution movement.
• Investigated protein denaturation (holomyoglobin to apomyoglobin) and enhanced mixing using square wave potentials.

Main Results:

• Electroosmosis was confirmed as the mechanism for solution transfer between theta tip channels.
• Demonstrated millisecond-timescale control over holomyoglobin denaturation.
• Achieved nearly complete mixing after a single square wave potential cycle, indicating enhanced turbulence.

Conclusions:

• Electroosmosis provides a versatile method for manipulating solutions within theta tips on millisecond timescales.
• This technique expands the capabilities of nESI emitters for pre-analysis sample modification.
• Eliminates the need for off-line sample preparation, increasing analytical workflow efficiency.