The photodegredation or photolysis of natural organic matter (NOM) in aqueous environments is an important component of the global carbon cycle, yet it is poorly understood due to the myriad of potential reactions occurring simultaneously in a water body. Photolysis can proceed “directly,” by absorption of a photon by a target organic compound, or “indirectly” via reaction with a photochemically produced reactive oxygen species (singlet oxygen, hydroxyl radical, hydrogen peroxide, etc.). Key to understanding the fate of NOM is an accurate description of the kinetics of photolysis, and eventual mineralization to CO<sub>2</sub>. Traditional methodologies for studying these kinetics require sampling an irradiated reaction chamber at regular intervals followed by extraction and often significant additional sample preparation prior to analysis with HPLC-MS. In our study, we use direct analysis in real time mass spectroscopy (DART), an atmospheric pressure ionization technique that requires minimal sample preparation to obtain mass spectrometric data. This approach creates a plasma at near-atmospheric pressures to form electronically-excited He atoms which stream out of the DART source and interact with water molecules to ionize analytes through protonation. Further, through the use of a novel front-end, we continuously deliver a controlled volume of our sample directly from our photoreactor to the DART stream without further preparation. With this technique, we are able to observe the real-time photodegradation of a series of NOM proxies— gallic acid, egallic acid, and tannic acid.  We then compare this data to traditional off-line analysis methods.  We will discuss the results from a series of experiments targeting first-order direct photolysis reactions and second-order reactions of proxies with various reactive oxygen species. The results from this work not only aid our understanding of this important system but highlight the general applicability of DART in obtaining real time kinetic data of first- and second-order reactions.<br/>

Photochemical reaction monitoring using direct analysis in real time mass spectrometry

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.