Comparison of the Wavelength Dependence of Probe Compounds Used for the Quantification of Hydroxyl Radical Production from Sodium Nitrite

Abstract

The principal objective of this experiment is to determine which probe compound, pCBA, benzene, or methanol, should be used when measuring the production of hydroxyl radical from sodium nitrite at various wavelengths of light. This topic is being investigated as accurate quantification of hydroxyl radical at varying spatial-temporal and climatic conditions, as modeled by the varying wavelengths of light, is important for understanding biogeochemical processes and pollutant dynamics. Three probe compounds (pCBA, benzene, and methanol) were combined with sodium nitrite, a known hydroxyl radical sensitizer, and exposed to LED light at varying wavelengths (255, 275, 295, 308, and 365 nm). The quantum yields of hydroxyl radical were determined by normalizing hydroxyl radical production by light intensity and the light absorption of sodium nitrite at the different wavelengths. The best probe at each wavelength is that which is most selective for the hydroxyl radical, measured by the smallest quantum yield. It was found that methanol is the only probe compound that is suitable for all the wavelengths studied. It was also the most selective probe compound, consistently measuring the lowest quantum yields for hydroxyl radical production.