Host: Abstracts of Annual Meeting of the Geochemical Society of Japan
Pages 226-
This paper discusses the use of ultraviolet (UV) light sources to oxidize dissolved organic carbon (DOC) from freshwater and seawater. The UV oxidation method is especially well-suited to seawater analysis, where dissolved salt concentrations far exceed DOC concentrations. The UV oxidation method commonly used for AMS seawater DOC - 14C analysis normally uses a UV light source in excess of 1000 W, however UV light sources that range from 8 W to 450 W show promise as a low-cost alternative. To demonstrate this, we prepared standard solutions with varying concentrations of the organic pH indicator, phenol red (C19H14O5S), and irradiated them under a UV light source for 30 minutes to 58 hours. Although the UV irradiation readily dissociated the phenol red, as observed by the loss of color in the solutions, it did not fully oxidize the carbon to CO2. However, we were able to convert 94% of the carbon to CO2 with the addition of hydrogen peroxide (H2O2). Hydrogen peroxide is especially effective because UV irradiation forms hydroxyl radicals, which are potent oxidants. The 8 W UV technique requires at least 24 hour irradiation times, however the light sources are relatively compact, do not produce appreciable heat or ozone, and a single light source can be shared between samples. We discuss the physics of UV oxidation under our experimental conditions and the design of a UV oxidation system and its applications. We also present results for dissolved humic acids and seawater samples processed under our system.
