Analytical procedure to determine both δ18O and δ17O of H2O2 in natural water and first measurements

An experimental technique has been developed to determine both δ18O and δ17O of hydrogen peroxide (H2O2) in natural water. The goal of this measurement is to develop a better understanding of peroxide chemical transformations in the atmosphere. Of particular relevance is the need for these measurements to interpret mass-independent isotopic anomalies observed in atmospheric aerosol sulfate. Combined peroxide and sulfate isotopic measurements may provide a new means to resolve atmospheric oxidative pathways. The technique utilizes the well-known reaction of H2O2 with KMnO4 in sulfuric acid solution, which oxidizes H2O2 to O2. Four liters of water sample ( 4 l) are degassed by a combination of helium sparging, ultrasonic agitation and pumping to quantitatively remove air dissolved in water. KMnO4 is then added to the solution and O2 produced during the oxidation reaction is recovered. Molecular oxygen is trapped and cryogenically purified in a series of molecular sieves for isotopic measurement. Industrially manufactured H2O2, sulfite oxidation by H2O2, auto-decomposition and partial oxidation of H2O2 show that all these samples are mass dependent, and obey the relationship δ17O=0.511δ18O. Rainwater samples collected at La Jolla, CA were analyzed using this method. The H2O2 is mass-independently fractionated and δ18O range from 21.9 to 52.5‰. We suggest that this range is due to the oxidation of sulfite in rain droplet and the mass-independent fractionation a result of gas-phase formation of H2O2. This is the first observation of a mass-independent isotopic composition in hydrogen peroxide