Sample pH Can Drift during Native Mass Spectrometry Experiments: Results from Ratiometric Fluorescence Imaging

Area of Science:

• Analytical Chemistry
• Biochemistry
• Physical Chemistry

Background:

• Nanoelectrospray ionization (nanoESI) is crucial for native mass spectrometry (MS).
• The electrolytic nature of nanoESI can generate redox byproducts, potentially altering sample chemistry.
• Native MS aims to study biomolecules in their solution state, making sample integrity critical.

Purpose of the Study:

• To quantify solution pH changes during nanoESI under native MS conditions.
• To investigate the influence of experimental parameters on pH alterations.
• To provide recommendations for mitigating pH effects in native MS experiments.

Main Methods:

• Utilized ratiometric fluorescence imaging with a pH-sensitive probe.
• Measured pH changes in sample solutions during nanoESI.
• Varied experimental parameters including applied potential and electrolyte concentration.

Main Results:

• Solution pH changes during nanoESI are dependent on experimental parameters.
• A strong correlation exists between pH change, nanoESI current, and electrolyte concentration.
• Negative potentials resulted in smaller pH shifts compared to positive potentials.

Conclusions:

• Electrochemical processes in nanoESI significantly affect sample pH.
• Optimizing nanoESI parameters can minimize solution pH drift.
• Understanding and controlling pH changes is essential for reliable native MS analysis of biomolecules.