Improvement of H2O2 Stabilization in Rainwater Samples

Peroxides collected in rainwater readily decompose in the natural matrix, consequently it is hard to
estimate their values present during precipitation events. For this reason, only few data concerning the
concentration of aqueous H2O2 in dew, cloud and rainwater are available. Therefore, it is necessary to
establish a sampling protocol under conditions that assure the real-time estimation of hydrogen
peroxide in rainwater samples. Hydrogen Peroxide was determined by a fluorometric method in
rainwater collected in fives sites in Mexico. Measured levels for all sampled sites were in agreement
with values reported by other authors for marine and continental sites. To establish a sampling
protocol, several methods reported for preservation of H2O2 in rainwater were assessed. Sampling
protocol proposed in this research involves forming fluorescent dimmer on-site immediately after
sample collection, and storing at dark and 4 ºC. This procedure gives a 10 days margin to perform
sample analysis, guarantying a minimal decomposition of H2O2 in rainwater samples (approximately
10%) and allowing more time to perform sampling campaigns even in remote sites. The other methods
evaluated (freezing, filtering, using acidified samplers, adding sodium stannate, and storing samples
and their fluorescent dimmer at 0ºC) do not exert any preservation effect over H2O2 levels in rainwater
samples.