Iodometry-Assisted Liquid Chromatography Electrospray Ionization Mass Spectrometry for Analysis of Organic Peroxides: An Application to Atmospheric Secondary Organic Aerosol.

Organic peroxides comprise a significant fraction of atmospheric secondary organic aerosol (SOA). Detection and quantification of particle-phase organic peroxides are highly challenging, and current efforts rely significantly on filter extraction and offline mass spectrometry (MS). Here, a novel technique, iodometry-assisted liquid chromatography electrospray ionization mass spectrometry (iodometry-assisted LC-ESI-MS), is developed and evaluated with a class of atmospherically relevant organic peroxides, α-acyloxyalkyl hydroperoxides, synthesized via liquid ozonolysis. Iodometry-assisted LC-ESI-MS unambiguously distinguishes organic peroxides, compensating for the lack of functional group information that can be obtained with MS. This technique can be versatile for a wide spectrum of environmental analytical applications for which a molecular-level identification of organic peroxide is required. Here, iodometry-assisted LC-ESI-MS is applied to the water-soluble organic carbon (WSOC) of α-pinene SOA. Unexpectedly, a limited number of detectable compounds in WSOC appear to be organic peroxides, despite the fact that spectroscopy-based iodometry indicates 15% of WSOC mass is associated with organic peroxides. This observation would be consistent with decomposition of multifunctional organic peroxides to small peroxides that can be quantified by spectroscopy-based iodometry but not by LC-ESI-MS. Overall, this study raises concerns regarding filter extraction-based studies, showing that assignment of organic peroxides solely on the basis of MS signatures can be misleading.