In Case You Missed It

By Lindsay Yee, UC Berkeley

Despite being some of the major products from organic peroxy (RO₂) radical chemistry, organic peroxides (ROOR or ROOH) have been challenging to detect and measure due to their labile nature.  The weak peroxy (O-O) bond makes organic peroxides susceptible to degradation during analysis techniques involving heat and/or extraction into solvents and water.  Organic peroxides are also known to participate in particle-phase accretion reactions, act as particle-phase oxidants in heterogenous chemistry, and be a source of reactive oxygen species that can cause oxidative stress in biological systems.  Increasing emphasis has been placed on developing methodologies that can be used to detect and identify organic peroxides with increased time resolution and chemical specificity.

In Qin et al., ES&T, 2023, the authors extend the use of matrix-assisted ionization in vacuum (MAIV) mass spectrometry along with real-time on- the-fly easy ambient sonic-spray ionization mass spectrometry (EASI-MS) for real-time characterization of organic peroxides and other products at the particle surface.  These techniques are applied to a model system of glutaric acid particle oxidation.  MAIV measurements show that at the surface layers, many peroxides are generated with higher relative magnitude than the non-peroxide products (i.e., alcohols and carbonyls) as compared to measurements by bulk particle measurements employing ultra-high-pressure liquid chromatography with high-resolution orbitrap mass spectrometry using heated electro- spray ionization (UHPLC-HESI-HRMS).  This has implications for thinking about how these abundant organic peroxides on particle surfaces may interact in a variety of settings.  They can result in greater amounts of ROS exposure within the human respiratory system (i.e., through decomposition upon water uptake during inhalation leaving surface-bound ROS), as compared to more limited exposure if organic peroxides are assumed to reside in the bulk interior of particles.  Further, heterogenous oxidation of SO₂ and aldehydes may also occur through interactions with organic peroxides presence at the surface layer.  Finally, they may influence chemistry in indoor environments where particles containing surface-bound peroxides are deposited to indoor surfaces and may interact with other adsorbed organics.

Read more in the literature:

Qin, Y., Perraud, V., Finlayson-Pitts, B. J. and Wingen, L. M.: Peroxides on the Surface of Organic Aerosol Particles Using Matrix-Assisted Ionization in Vacuum (MAIV) Mass Spectrometry, Environ. Sci. Technol., 57(38), 14260–14268, doi:10.1021/acs.est.3c02895, 2023.