EPR determination of the content of vanadium and vanadylporphyrins in petroleum products

High Field Electron Paramagnetic Resonance Characterization of Electronic and Structural Environments for Paramagnetic Metal Ions and Organic Free Radicals in Deepwater Horizon Oil Spill Tar Balls

“…The X-band spectrum (Figure , left) shows two distinct features: (i) a sharp symmetric line with a g -value (2.0025 ± 0.0005) very close to the free-electron g -value (2.0023) with a peak-to-peak line width of Δ H p‑p ≈ 0.6 mT (6 G), due to the presence of a hydrocarbon free radical, and (ii) a set of two hyperfine octets, with significant overlap of lines around the free radical peak. Although the spectrum could be simulated with known parameters (see Table ), a much better resolved spectrum was obtained at 240 GHz (Figure , right): (i) the vanadyl hyperfine octets − ,− are separately resolved and displaced from the FR-line; (ii) a new 6-line hyperfine structure centered at g = 1.9987 flanks the free radial line; and (iii) the free radical line is broad (Δ H p‑p ≈ 3 mT, 30 G) and (surprisingly) is slightly asymmetric (as discussed in more detail below). The parallel and perpendicular hyperfine lines of [V–O] 2+ could be fitted to a simulated spectrum, thereby enabling much more accurate determination of the spin Hamiltonian parameters.…”

“…To determine the chemical structure of the vanadyl complex in the tar balls and marine asphalt, we used vanadyl octaethylporphyrin (VOOEP) as a standard, because earlier literature has indicated the possibility of such a structure for the ubiquitously present vanadium complex in crude oil asphaltenes. − It is necessary to choose a solvent in which VOOEP could be dissolved at dilute concentration comparable to that for the vanadium complex in the NIST standard and the tar balls. Simply spiking the tar balls and marine asphalt with VOOEP did not suffice, because the concentration of the paramagnetic center ([V–O] 2+ ) in VOOEP is so high that the EPR signal is exchange-broadened and not directly comparable to the signals from the field samples.…”

“…Because [V–O] 2+ contains a 3d 1 unpaired electron, it is paramagnetic and hence accessible by electron paramagnetic resonance (EPR) spectroscopy. Indeed, a recent EPR study by Kiruri et al of tar balls collected from the Gulf region followed several earlier studies on crude oil and petroleum asphaltenes. − Biktagrov et al published an EPR study of rotational mobility of vanadyl porphyrin complexes in crude oil asphaltenes . Their experiments, like those of ref , were conducted at X-band with the assumption of isotropic rotational diffusion.…”

“…We also provide quantitative measurements of the vanadyl and Mn concentrations in the tar balls and marine asphalt volcano sample, based on NIST (National Institute of Standards and Technology) standards, and show that the organic radical moiety in the crude and the tar balls is not a polymerized, knotted spherical structure but rather an axially symmetric disk-shaped organic compound with the unpaired electron delocalized over the molecular frame. The introduction of high-field EPR to this field opens up a new approach for characterizing paramagnetic metal complexes and organic moieties in source and weathered petroleum crude oils, as well as other fossil fuel-related environmental − samples.…”

Chemiluminescence Flow System for Vanadium(V) With Immobilized Reagents

“…Vanadium in trace amounts not only plays an important role in industry and biochemistry, but also is an environmental pollutant and occupational hazard. For its measurement, many methods have been developed, such as spectrophotometry, 1,2 titrimetry, 3 fluorimetry, 4 X-ray fluorescence spectrometry, 5 gray spectrometry, 6 inductively coupled plasma mass spectrometry, 7 electron spin resonance spectrometry, 8 atomic absorption spectrometry, 9 atomic emission spectrometry, 10 chromatography, 11 neutron activation analysis, 12 gravimetry, 13 thermometry 14 and electrochemical analyses. 15,16 Chemiluminescence (CL) analysis offers high sensitivity, wide linear range and simple instrumentation and has been applied successfully to the determination of vanadium by using luminol, 17,18 lucigenine, 19 quinolinic hydrazide, 20 cinchomeronic hydrazide 21 and peroxymonosulfate 22 as analytical reagents.…”