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).

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The hydrogenation of alkenes by heterogeneous catalysts has been studied for 80 years. The foundational mechanism was proposed by Horiuti and Polanyi in 1934 and consists of three steps: (i) alkene adsorption on the surface of the hydrogenated metal catalyst, (ii) hydrogen migration to the β-carbon of the alkene with formation of a σ-bond between the metal and α-C, and finally (iii) reductive elimination of the free alkane. Hundreds of papers have appeared on the topic, along with a number of variations on the Horiuti–Polanyi mechanism. The second step is highly reversible, leading to extensive deuterium–hydrogen exchange when D2(g) is used. This paper describes the investigation of gas-phase reactions between deuterium and 1-butene using a supported palladium catalyst under ambient laboratory conditions and how the results are consistent with the Horiuti–Polanyi mechanism. An Excel spreadsheet for modeling the extent and distribution of deuteration within butane-d x is described. Interested readers could develop a laboratory or research experience based on results presented here. The results are also suitable for inclusion in an upper-division chemistry course in which organometallic chemistry or reaction mechanisms involving heterogeneous catalysts are discussed. The catalyst tubes are inexpensive and easy to construct. Analysis of the butane produced by 1H NMR and GC–MS leads to numerous conclusions in support of the Horiuti–Polanyi mechanism.

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