Identification of persistent oil residues in Prince William Sound, Alaska using rapid spectroscopic techniques.

Spectroscopic techniques including X-ray fluorescence (XRF) and attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) are used to examine oil residues persisting on shorelines in Prince William Sound that originate from the 1989 Exxon Valdez oil spill and oil released as a consequence of the 1964 Great Alaska earthquake. When coupled to classification models, ATR-FTIR and XRF spectral data can be used to distinguish between the two sources of oil with 92% and 86% success rates for the two techniques respectively. Models indicate that the ATR-FTIR data used to determine oil source includes the CO stretch, the twisting-scissoring of the CH2 group, and the CC stretch. For XRF data, decision tree models primarily utilize the abundance of nickel and zinc present in the oil as a means to classify source. This approach highlights the utility of rapid, field-based spectroscopic techniques to distinguish different inputs of oil to coastal environments.

Chemical characterization of natural and anthropogenic-derived oil residues on Gulf of Mexico beaches.

Oil residues originating from the Deepwater Horizon (DWH) incident persist on Gulf of Mexico beaches alongside oil from offshore industrial activity, natural seepage, and asphalt from parking lots and roads. To determine the primary differences in the chemical composition of these oil residues, a variety of samples were collected from beaches from Florida to Alabama over a two-year period from 2015 to 2017. Bulk chemical characteristics of the oil residues were examined via gas chromatography with flame ionization detection (GC-FID) and mass spectrometry (GC-MS), as well as thin layer chromatography with flame ionization detection (TLC-FID), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR). These bulk chemical analyses revealed features unique to the different sample types, expanding our understanding of the chemical composition and variability of persistent oil residues, and providing a means to detect and monitor their long-term fate in the coastal environment.

The Bend+Libration Combination Band Is an Intrinsic, Collective, and Strongly Solute-Dependent Reporter on the Hydrogen Bonding Network of Liquid Water.

Water is an extensively self-associated liquid due to its extensive hydrogen bond (H-bond) forming ability. The resulting H-bonded network fluid exhibits nearly continuous absorption of light from the terahertz to the near-IR region. The relatively weak bend+libration water combination band (centered at 2130 cm-1) has been largely overlooked as a reporter of liquid water's structure and dynamics despite its location in a convenient region of the IR for spectroscopic study. The intermolecular nature of the combination band leads to a unique absorption signal that reports collectively on the rigidity of the H-bonding network in the presence of many different solutes. This study reports comprehensively how the combination band acts as an intrinsic and collective probe in various chemically and biologically relevant solutions, including salts of varying character, denaturants, osmolytes, crowders, and surfactants that form reverse micelles and micelles. While we remark on changes in the line width and intensity of this combination band, we mainly focus on the frequency and how the frequency reports on the collective H-bonding network of liquid water. We also comment on the "association band" moniker often applied to this band and how to evaluate discrete features in this spectral region that sometimes appear in the IR spectra of specific kinds of aqueous samples of organic solutes, especially those with very high solute concentrations, with the conclusion that most of these discrete spectral features come exclusively from the solutes and do not report on the water. Contrasts are drawn throughout this work between the collective and delocalized reporting ability of the combination band and the response of more site-specific vibrations like the much-investigated OD stretch of HDO in H2O: the combination band is a unique reporter of H-bonding structure and dynamics and fundamentally different than any local mode probe. Since this band appears as the spectroscopic "background" for many local-mode reporter groups, we note the possibility of observing both local and collective solvent dynamics at the same time in this spectral region.