It is well known that in surface waters, the photo-irradiation of dissolved organic matter (DOM) produces hydroxyl radicals (●OH). There are several hypothesis as to how ●OH could be photochemically formed, including via reactions involving benzoic acids derivatives and through other excited state reactions. ●OH play an important role in the fate of contaminants in surface waters as they have a high reactivity with most contaminants. Additionally to the formation of ●OH, lower energy hydroxylators (LEH) are also produced during DOM photo-irradiation. These LEH are far less studied than ●OH, but it is known that they have a lower reactivity when compared to ●OH. One hypothesis regarding these LEH is that they are formed through exited triplet states of quinones. In this study, we present an investigation of potential methods to quantify and differentiate ●OH and LEH. The first method is the use of a quencher such as isopropanol or methanol to quench all hydroxylating capacity in the system. The second method is to use a probe compound such as benzene or benzoic acid to quantify ●OH and LEH. In the latter case, as LEH lifetime are limited in water, the concentration of the probe compound matters and it is possible to distinguish between ●OH and LEH by varying the concentration of the probe compound. Literature results often presents the quantification of hydroxyl radical using probe compounds without distinguishing between ●OH and LEH. As the quantification of LEH is dependent on the concentration of the probe, this has the important consequence that the determination of parameters such as the ●OH quantum yield (Φ●OH) can yield different results depending on the experimental condition used.

On the quantification of hydroxyl radical and lower energy hydroxylator from dissolved organic matter photoirradiation

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

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