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Sunlight-induced molecular changes have been observed in two samples of dissolved organic matter (DOM) collected in the Cape Fear River system, North Carolina, USA. The molecular composition of a water sample collected in the Black River (sample B210, salinity 0) and another water sample collected within the Cape Fear River estuary (sample M61, salinity 13.7) were analyzed using an ultrahigh resolution 9.4 Tesla (T) electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer. Additionally, the Ultraviolet/Visible (UV/vis) absorbance as well as the excitation emission matrix (EEM) fluorescence spectra were determined to identify changes in the optical properties associated with photochemical reactions of the chromophoric DOM (CDOM). The molecular formulas forthe Cape Fear River Estuary (M61) sample before the irradiation experiments indicated the presence of highly aromatic compounds which were not present in the unirradiated Black River sample (B210). These aromatic compounds, with oxygen-subtracted double bond equivalents (DBE-O) values greater than nine, are more photoreactive and readily photodegraded relative to saturated compounds. Compounds with DBE-O values below nine are less photoreactive. The UV/vis absorbance and EEM fluorescence results supported this different photodegradation behavior, suggesting that the photoreactivity of CDOM is highly dependent on the molecular composition of the CDOM.

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Chemiluminescence (CL) of acridinium esters (AE) has found widespread use in analytical chemistry. Using the mechanism of the reaction of H2O2 with 10-methyl-9-(p-formylphenyl)acridinium carboxylate trifluoromethanesulfonate and a modified flow injection system, the reaction rates of each step in the mechanism were evaluated and used in a kinetic model to optimize the analysis of H2O2. Operational parameters for a flow injection analysis system (reagent pH, flow rate, sample volume, PMT settings) were optimized using the kinetic model. The system is most sensitive to reaction pH due to competition between AE hydrolysis and CL. The optimized system was used to determine H2O2 concentrations in natural waters, including rain, freshwater, and seawater. The lower limit of detection varied in natural waters, from 352 pM in open ocean seawater (mean, 779 pM +/- 15.0%, RSD) to 58.1 nM in rain (mean, 6,340 nM +/- 0.92%, RSD). The analysis is specific for H2O2 and is therefore of potential interest for atmospheric chemistry applications where organoperoxides have been reported in the presence of H2O2.