Peptide Oxidation Induced by Liquid-Solid Contact Electrification as Revealed in Liquid Microjunction-Surface...

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Surface Science

Background:

• Analyte oxidation is a known issue in mass spectrometry (MS) methods.
• Previous studies linked oxidation to electrochemical processes in electrospray ionization (ESI) and related ambient ionization techniques.

Purpose of the Study:

• To investigate the cause of reproducible peptide oxidation observed with a liquid microjunction-surface sampling probe (LMJ-SSP).
• To identify methods for minimizing analyte oxidation during sample preparation for MS.

Main Methods:

• Utilized a homebuilt liquid microjunction-surface sampling probe (LMJ-SSP) platform.
• Analyzed peptide standards under varying experimental conditions.
• Systematically investigated droplet drying processes on solid surfaces.

Main Results:

• Reproducible peptide oxidation was observed, but not attributed to electrochemical oxidation or corona discharges.
• Oxidation was induced by liquid-solid electrification processes during droplet drying.
• Decreasing water content, avoiding hydroxylated substrates, and adding antioxidants (e.g., ascorbic acid) reduced oxidation.

Conclusions:

• Analyte oxidation in LMJ-SSP analysis originates from droplet evaporation on surfaces via liquid-solid electrification.
• Optimizing sample solvent composition and substrate choice are key to minimizing oxidation.
• Findings are relevant for all MS methods involving sample drying on substrates.