Steven M. Rowland

Chromatographic enrichment and subsequent separation of nickel and vanadyl porphyrins from natural seeps and molecular characterization by positive electrospray ionization FT-ICR mass spectrometry.

We report a novel chromatographic method to enrich and separate nickel and vanadyl porphyrins from a natural seep sample and combine molecular level characterization by positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Vanadyl and nickel porphyrin model compound elution from primary secondary amine (PSA) stationary phase combined with UV-vis spectroscopy confirms enrichment and subsequent fractionation of nickel and vanadyl porphyrins into polarity-based subfractions. A more than 100-fold increase in signal-to-noise ratio for nickel porphyrins enables unequivocal elemental composition assignment confirmed by isotopic fine structure for all isotopes >1% relative abundance, and the first mass spectral identification of (61)Ni porphyrin isotopologues derived from natural seeps. Oxygen-containing vanadyl porphyrins and sulfur-containing vanadyl porphyrins are isolated in the same fraction simultaneously from the same sample. We provide the first chromatographic evidence of carboxylic acid functionalities peripheral to the porphyrin core, in agreement with previous studies.

Characterization of copolymers and blends by quintuple-detector size-exclusion chromatography.

The properties imparted, oftentimes synergistically, by the different components of copolymers and blends account for the widespread use of these in a variety of industrial products. Most often, however, processing and end-use of these materials (especially copolymers) is optimized empirically, due to a lack of understanding of the physicochemical phase-space occupied by the macromolecules. Here, this shortcoming is addressed via a quintuple-detector size-exclusion chromatography (SEC) method consisting of multiangle static light scattering (MALS), quasi-elastic light scattering (QELS), differential viscometry (VISC), ultraviolet absorption spectroscopy (UV), and differential refractometry (DRI) coupled online to the separation method. Applying the SEC/MALS/QELS/VISC/UV/DRI method to the study of a poly(acrylamide-co-N,N-dimethylacrylamide) copolymer in which both monomer functionalities absorb in the same region of the UV spectrum, we demonstrate how to determine the chemical heterogeneity, molar mass averages and distribution, and solution conformation of the copolymer all in a single analysis. Additionally, through the various mutually independent conformational and architectural metrics provided by combining the five detectors, including the fractal dimension (derived from two different detector combinations), two different dimensionless size parameters, the chemical heterogeneity, and the persistence length, it is shown that the monomeric arrangement is more alternating than random at lower molar masses, thus causing the copolymer to adopt a more extended conformation in solution in this molar mass (M) regime. At high M, however, the copolymer is shown to be and to behave more like a random coil homopolymer, after passing through a 250 kg mol(-1)-broad region of intermediate chain flexibility. Thus, the combination of five detectors provides a unique means by which to determine absolute properties of the copolymer, solution-specific physical behavior, and the underlying chemical basis of the latter. The quintuple-detector method was also extended to the study of blends of polyacrylamide and poly(N,N-dimethylacrylamide) homopolymers to quantitate their molar mass, solution conformation, and chemical heterogeneity and to shed light on the breadth of the distributions of the component species. The method presented should be applicable to the study of copolymers and blends in which either one or both component moieties or polymers absorb in the UV region and can be implemented using not only SEC but other size-based separation methods as well.

Characterization of Highly Oxygenated and Environmentally Weathered Crude Oils by Liquid Chromatography Fourier Transform Ion Cyclotron Mass Spectrometry (FT-ICR MS)

Heavy and biodegraded oils exhibit an ever increasing oxygen complexity. Electrospray ionization (ESI) coupled to FT-ICR MS highlights the most acidic and basic oxygen species; however, quantitative and qualitative information about less polar oxygenated compounds is essential to understand both the source and, potentially, the modification pathways for oxygenated crude oils. Liquid chromatography (LC) is complementary to FT-ICR MS to deconvolve crude oils according to oxygen functionality, thereby enriching oxygen species that are not easily ionized or are present in low abundance. Ketones and carboxylic acids dominate most environmentally modified crude oils; however, phenols and polyphenols are also important intermediates in both biotic and abiotic modifications. Moreover, due to the nature of the refinement process, oxygen-containing species and their intermediates can serve as chemical tracers in produced water streams and areas of rapid thermal changes that lead to gum or deposit formation. Here, w...