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Can Hydroxyl Radicals Be Spontaneously Formed at the Air-Water Interface of Microdroplets? A Spray Ionization Mass
1Department of Chemistry, Graduate School of Science and Technology, University of Tsukuba, Tsukuba 305-8571, Japan.
Abstract:
Recent studies have proposed that hydroxyl radicals (OH) could be formed at the air-water interface (AWI) of aqueous microdroplets. We performed spray ionization mass spectrometry investigations using benzoate (BA-) as an OH scavenger to determine whether OH was spontaneously formed at the AWI of microdroplets. The mass spectrometric signal for hydroxy-BA-, a major product of BA- + OH, was confirmed in the presence of OH(g). However, that signal was undetected in water microdroplets containing BA- in the absence of OH(g). We separately confirmed the formation of hydroxy-BA- by detection of its signal from an aqueous solution of BA-/FeCl2/H2O2, but no detection was observed from an aqueous solution of BA-/FeCl2. Experiments using DMSO as an alternative OH-scavenger also showed no evidence for spontaneously formed OH at the AWI of microdroplets. We derived an upper limit to the concentration of spontaneously formed OH to be ∼0.2 μM under our experimental conditions.
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