Fluorescence Spectroscopy Reveals Ubiquitous Presence of Oxidized and Reduced Quinones in Dissolved Organic Matter

Abstract

Excitation-emission matrixes (EEMs) of 379 dissolved organic matter (DOM) samples from diverse aquatic environments were modeled by parallel factor analysis (PARAFAC). Thirteen components likely representing groups of similarly fluorescing moieties were found to explain the variation in this data set. Seven of the thirteen components were identified as quinone-like based on comparison of their excitation and emission spectra to spectra of model quinones. These quinone-like fluorophores were found to vary in redox state and degree of conjugation. Two components were identified as amino acid-like based on comparison to tyrosine and tryptophan fluorescence spectra. The other four components are not yet associated with any class of molecules. The quinone-like fluorophores account for about 50% of the fluorescence for every sample analyzed, showing that quinone-like fluorophores are an important and ubiquitous fluorescing moiety and in natural waters. Further, the distribution of the quinone-like fluorophores was evaluated as a function of environmental and laboratory redox gradients. Under reducing conditions, the contribution of the reduced quinone-like fluorophores increased concurrentwith a decrease in the oxidized quinone-like fluorophores, indicating that DOM fluorescence is a function of redox state of quinone-like moieties. Lastly, a ratio of two quinone-like fluorophores was found to explain the variation in the fluorescence index. These results provide new insight into the redox reactivity of DOM and have implications for the application of fluorescence spectroscopy as a tool to characterize DOM.

Moving towards a technical specification for fluorescence excitation-emission mapping and absorbance analysis of colored dissolved organic matter

“…As mentioned above, the purpose of the spectral corrections and EEM-processing is to make the identification and quantification easier of the CDOM components that are usually based on a reference-component library. Here we focus attention on a popular and promising library-based multivariate technique for CDOM analysis, namely, PARAFAC, which has been documented extensively by researchers including many using HORIBA's fluorescence instruments [1,[3][4][5]. Importantly the AquaLog ® software offers direct access to a MatLab ® console for purposes of processing data using the PARAFAC tools in N-way Toolbox, a public-domain package especially developed for CDOM analysis [4].…”

“…Importantly the AquaLog ® software offers direct access to a MatLab ® console for purposes of processing data using the PARAFAC tools in N-way Toolbox, a public-domain package especially developed for CDOM analysis [4]. The modeling advantages of PARAFAC center on its ability to simultaneously evaluate the EEM data as a matrix, and to envelop multiple (often hundreds) of EEMs simultaneously for increased statistical significance [3][4][5]. PARAFAC has been successful at identifying a wide range of CDOM components including humic and fulvic acids, tryptophan-and tyrosine-like substances, quinones, several polycyclic aromatic hydrocarbons, and distinguishing microbial, marine and terrestrial CDOM sources.…”

“…Current methodologies to separate, identify and quantify the components have focused on conventional non-linear least-squares spectral deconvolution as well as a variety of multivariate techniques [1][2][3][4][5][6]. The latter multivariate methods include, among others, Partial Least Squares (PLS), Principal Component Analysis (PCA), and the recently popularized Parallel Factor Analysis or PARAFAC method, which we focus on in this review.…”

Characteristics of dissolved organic matter in the Upper Klamath River, Lost River, and Klamath Straits Drain, Oregon and California

“…FI values typically range from 1.3 to 1.9. Low values are typically associated with terrestrially derived material, such as plant and soil matter, and high values are associated with microbial sources, such as release from bacterial and algal cells (McKnight and others, 2001;Cory and McKnight, 2005).…”

Phototransformation of the sunlight filter benzophenone-3 (2-hydroxy-4-methoxybenzophenone) under conditions relevant to surface waters

“…AQ2S was used as CDOM proxy, to assess reactivity between BP3 and 3 CDOM*. Reasons for this choice are the widespread occurrence of quinones in CDOM and the fact that irradiation of AQ2S, unlike other triplet sensitisers, does not yield interfering transients such as • OH and 1 O 2 (Cory and McKnight, 2005;Maddigapu et al, 2010). AQ2S initial concentration was 0.1 mM, to limit the additional complication represented by reaction between 3 AQ2S* and ground-state AQ2S (Bedini et al, 2012a).…”