Natural dissolved organic matter (DOM) in aquatic systems plays many environmental roles: providing building blocks and energy for aquatic biota, acting as a sunscreen in surface water, and interacting with anthropogenic compounds to affect their ultimate fate in the environment. Such interactions are a function of DOM composition, which is difficult to ascertain due to its heterogeneity and the co-occurring matrix effects in most aquatic samples. This review focuses on current approaches to the chemical structural characterization of DOM, ranging from those applicable to bulk samples and in situ analyses (UV-visible spectrophotometry and fluorescence spectroscopy) through the concentration/isolation of DOM followed by the application of one or more analytical techniques, to the detailed separation and analysis of individual compounds or compound classes. Also provided is a brief overview of the main techniques used to characterize isolated DOM: mass spectrometry (MS), nuclear magnetic resonance mass spectrometry (NMR) and Fourier transform infrared spectroscopy (FTIR).

No abstract

Dissolved organic matter (DOM) is a complex mixture of molecules found ubiquitously in freshwater and saltwater environments. Its structures contain valuable information content on the sources of molecules as well as the mechanisms at work within an aquatic ecosystem. Recent advancements in high resolution mass spectrometry and liquid chromatography have made inroads into determinations of the molecular structures within DOM. Such analyses, however, generally require a prior step to concentrate/isolate DOM, and this step often limits the number of samples that can be analyzed. This study has developed a fast method to concentrate DOM on commercially available online solid phase extraction (SPE) cartridges, which can be directly eluted onto an HPLC‐MS system. This rapid solid phase extraction (RSPE) method requires less sample (10‐100 mL) than previous SPE methods for DOM isolation. Additionally, this study tested a suite of SPE phases to find a combination that improves DOM recovery as compared with commonly used approaches. When a polystyrene divinylbenzene phase (RP‐1) was coupled with an activated carbon (CAR) phase, recoveries were found to be significantly higher than in previous SPE studies relying upon single phases. RSPE was tested for a diverse set of salty and freshwater samples with recoveries ranging from 46% to 78% of the total DOC. It was also tested on a suite of model compounds (including caffeine) and should be applicable to anthropogenic compounds in aquatic environments, although, in such cases, optimization may be needed to minimize the natural organic matter signal that was maximized in this study.

Kinetic expressions for the aqueous reactions of chlorine with phenanthrene (pH 3-10), fluorene (pH 3-5), and fluoranthene (pH 3-5) have been developed. At pH 3-5 the rate of reaction of each PAH studied could be related to the chlorine concentration (-d[PAH]). Phenanthrene, also studied at high pH values (pH >8.8), followed a rate expression consistent with pseudo-first-order kinetics (-d[phen]). The overall rate expression that was developed for phenanthrene is suggested as a model for correlating the rates of reaction of chlorine with polynuclear aromatic compounds in water over the entire pH range (pH 3-10) that might reasonably be encountered during disinfection. This overall expression is Cl•, and O" (24).The arene oxide (phenanthrene 9,10-oxide) was the predominant phenanthrene product at pH 54 while phenanthrene-9,10-dione and 9-chlorophenanthrene were the major products at pH S4.

No abstract