Quantitative detection of hydrogen peroxide in rain, air, exhaled breath, and biological fluids by NMR spectroscopy.

Hydrogen peroxide (H 2 O 2 ) plays a key role in environmental chemistry, biology, and medicine. H 2 O 2 concentrations typically are 6 to 10 orders of magnitude lower than that of water, making its quantitative detection challenging. We demonstrate that optimized NMR spectroscopy allows direct, interference-free, quantitative measurements of H 2 O 2 down to submicromolar levels in a wide range of fluids, ranging from exhaled breath and air condensate to rain, blood, urine, and saliva. NMR measurements confirm the previously reported spontaneous generation of H 2 O 2 in microdroplets that form when condensing water vapor on a hydrophobic surface, which can interfere with atmospheric H 2 O 2 measurements. Its antimicrobial activity and strong seasonal variation speculatively could be linked to the seasonality of respiratory viral diseases.