An Alternative Explanation for Ions Put Forth as Evidence for Abundant Hydroxyl Radicals Formed Due to the Intrinsic Electric Field at the Surface of Water Droplets.

ABSTRACT: Ions at m/z 36 and +17 Da higher in mass than protonated caffeine and melatonin have been put forth as evidence for spontaneous formation of abundant OH^• in water droplets due to the high electric field at the surface. Nanoelectrospray ionization was used to produce ions from aqueous caffeine and melatonin solutions under soft mass spectrometer sampling conditions. When the source housing was purged with N₂ gas, abundant protonated caffeine was produced along with a trace abundance of an ion that is +17 Da higher in mass. Accurate mass measurements are consistent with an elemental composition of (caffeine + H + NH₃)⁺ and are sufficiently accurate to rule out the previous identification of this ion as (caffeine + H + OH)^+•

SUBMITTER: Chen CJ 

PROVIDER: S-EPMC12368832 | biostudies-literature | 2025 Aug

REPOSITORIES: biostudies-literature