Coupling Aqueous Phase Chemical Actinometry with EPR Spectroscopy: An Approach for Probing Photochemical Processes at...

Area of Science:

• Environmental Chemistry
• Photochemistry
• Analytical Chemistry

Background:

• Investigating ambient sample photochemistry and photoproduced radicals is crucial.
• Electron paramagnetic resonance (EPR) spectroscopy is a key technique for radical detection.
• Accurate quantification of photon flux is essential for in situ photochemical studies.

Purpose of the Study:

• To develop and validate a method using chemical actinometers for photon flux determination in in situ EPR experiments.
• To correct EPR measurements for solar light exposure using a novel approach.
• To assess the photochemical activity of sea-surface microlayer (SML) samples.

Main Methods:

• Utilized chemical actinometers for photon flux measurement in EPR experiments.
• Employed spin-trapping with TEMP-OH for singlet oxygen (1O2) detection.
• Investigated photosensitization using Protoporphyrin IX (PPIX) and rose bengal (RB).
• Applied the developed method to analyze SML samples for sunlight-induced oxidant formation.

Main Results:

• Achieved consistent in situ EPR (IEPR) values between 1.3–1.6 × 10-8 mol photons L-1 s-1 for PPIX and RB systems.
• Identified pH < 2 as a potential interference due to TEMP-OH protonation.
• Observed stabilization of PPIX solutions by TEMP-OH, mitigating aggregation effects.
• Quantified sunlight-induced oxidant formation rate in SML samples at (3.8 ± 0.5) × 10-8 M s-1.

Conclusions:

• The developed chemical actinometry method is effective for quantifying photon flux in in situ EPR.
• The study demonstrates significant photochemical activity in sea-surface microlayer samples.
• The findings provide a robust approach for future photochemical investigations of environmental samples.