Project Overview

Overview

In January 2016, Dr. Andres Campiglia at the University of Central Florida was awarded an RFP-V grant of $1,523,285 to lead the GoMRI project entitled, “A Combined Analytical and Synthetic Approach Based on Line Narrowing Spectroscopy for Specific Isomer Determination of Petroleum Oil Spills” consisted of approximately 12 research team members (including students).   The large volume of crude oil released into the Gulf of Mexico by the Deepwater Horizon (DHW) accident has raised considerable concerns over potential ecosystem impacts. The dispersion of harmful oil components into the ocean waters could pose long term risks to flora and fauna. One of the main concerns focuses on polycyclic aromatic hydrocarbons (PAHs). Since several PAHs are toxic and a subset exhibit carcinogenic activity, the exposure of human populations to hazardous concentration levels may lead to unreasonable health risks. Particular attention has been paid to the sixteen PAHs currently listed as priority pollutants by the Environmental Protection Agency (EPA). Their chemical structures consist of two or more un-substituted benzene rings with molecular weights (MW) ranging from approximately 128 to 278 g mol-1. Since their toxicity varies widely depending upon the isomer, data on total PAH levels is not particularly useful in determining human health risks. It is important to determine the most toxic PAHs unambiguously, even if they are present at much lower concentrations than their less toxic isomer   This proposal tackles a different aspect of PAHs analysis as it focuses on detection and characterization of higher-molecular weight PAHs (HMW-PAHs), i.e. PAHs with MW equal or higher than 302 g mol-1. The HMW-PAHs isolated from environmental and combustion-related samples exhibit mutagenic activity and petroleum transformation products from HMW-PAHs persist in the environment longer than their lighter counterparts. Studies have shown significant sedimentation of HMW-PAHs that may be increased with the addition of dispersants in a coastal setting. Their continued monitoring will ensure that HMW-PAHs present in sediments are not being redistributed and accumulating through the food chain.   Individual isomers of HMW-PAHs are not routinely identified or quantified. Difficulties in the determination of HMW-PAHs arise from their low concentration levels in environmental samples compared to those of the priority pollutant PAHs. The number of isomers increases dramatically with each additional aromatic ring, which makes separation and identification difficult by gas chromatography-mass spectrometry and liquid chromatography. Finally, there are still only a limited number of commercially available reference standards for HMW-PAHs, which hinders their identification and quantification. Since their carcinogenic properties can vary by orders of magnitude from one isomer to another, conclusions drawn from risks assessment studies could be seriously in error if the analytical characterization techniques cannot distinguish isomers.

  The development of a robust approach with the ability to efficiently and reliably detect and quantify specific isomers of HMW-PAHs would be a significant analytical breakthrough. The goal of this proposal, then, is to fulfill this gap. The specific research goals are the following: (a) unambiguously determine HMW-PAHs with MW 302 in complex environmental extracts from the Gulf of Mexico using the multidimensional laser excited time-resolved Shpol’skii spectroscopy (LETRSS) technique; (b) synthetize pure standards of MW 302 currently unavailable from commercial sources; and (c) extend the developed approach to the analysis of specific isomers of HMW-PAHs with MW > 302 including alkylated PAHs (APAHs) and sulfur containing PAHs (PASHs).   When compared to un-substituted PAHs, APAHs comprise a relatively large fraction of the total number and mass of PAHs found in crude oil and crude-contaminated seafood samples. Sulfur is the principal heteroatom in coal, crude oil, tar and their by-products. Thus, to fully understand the environmental implications of the DWH accident, the ideal technique should be able to determine isomers of APAHs and PASHs   Through collaborations with other scientists involved in the Gulf of Mexico Research Initiative, this proposal will provide environmental scientists will the ability to track down specific PAH isomers and fully understand their environmental fate in the Gulf of Mexico.

 

Research Highlights

As of December 31, 2019, this project’s research resulted in 9 peer-reviewed publications, 30 scientific presentations, and 23 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be made available to the public. The project also engaged 9 PhD level students over its award period. Significant outcomes of this project’s research according to GoMRI Research Theme are highlighted below.

 

• An analytical strategy was developed for the chromatographic analysis of polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs (A-PAHs), polycyclic aromatic sulfur heterocycles (PASHs) and their alkyl-substituted derivatives (A-PASHs) in complex environmental extracts. The new strategy consists of sample fractionation via normal-phase liquid chromatography (NPLC) and fraction interrogation via either reversed-phase liquid chromatography (RPLC) or gas chromatograph-mass spectrometry (GC-MS). When GC-MS interrogates NPLC fractions, the qualitative parameters available for compound identification are NPLC and GC retention times, main mass ion peaks and mass fragmentation patterns. When RPLC interrogates NPLC fractions, compounds can be identified on the bases of NPLC and RPLC retention times, spectral profiles recorded at maximum excitation and fluorescence wavelengths and/or synchronous fluorescence spectra recorded at characteristic wavelength offsets. This strategy is well-suited for the analysis of a wide range of molecular masses varying from three-ring to seven-ring polycyclic aromatic compounds. 

 

• We have successfully developed methodology for the unambiguous determination of HMW-PAHs with molecular mass 302 Da. The new method is based on the analysis of RPLC fractions via laser-excited time-resolved Shpol’skii spectroscopy (LETRSS) at 77 K and 4.2 K. The high spectral resolution achieved in Shpol’skii matrixes at cryogenic temperatures provides vibrational information for fingerprint identification of PAH isomers with the same molecular mass. Characteristic fluorescence lifetimes add qualitative information to wavelength assignments for accurate quantitative determinations. Data sets consisting of excitation and emission spectra and fluorescence lifetimes at 77 K and 4.2 K are a publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC;https://data.gulfresearchinitiative.org/pelagos-symfony/data-discovery). Those data sets make possible to determine unambiguously the 23 commercially available MM 302 Da PAH isomers in environmental extracts at the parts-per-billion (ng.mL-1) concentration levels.

 

• The database of the National Institute of Standards and Technology (NIST) identifies the molecular structures of 88 possible PAH isomers with MM 302 Da. Of this library, only 23 isomers are commercially available as pure standards. We have synthetized five new PAH isomers with MM 302 Da, namely dibenzo[a,l]fluoranthene, dibenzo[a,j]fluoranthene, dibenzo[b,l]fluoranthene, naphtho[1,2-j]fluoranthene and naphtho[2,1-j]fluoranthene. With the exception of dibenzo[a,j]fluoranthene, the other four PAHs showed strong fluorescence at 77K and 4.2K. Data sets consisting of excitation and emission spectra and fluorescence lifetimes at 77 K and 4.2 K are a publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC;https://data.gulfresearchinitiative.org/pelagos-symfony/data-discovery). Limits of detection and the sub-parts-per-billion level were obtained for dibenzo[a,l]fluoranthene, dibenzo[b,l]fluoranthene, naphtho[1,2-j]fluoranthene, and naphtho[2,1-j]fluoranthene. For the first time, dibenzo[b,l]fluoranthene was identified in a standard reference material (SRM 1597a) from NIST. Although the toxicity of dibenzo[b,l]fluoranthene has not been investigated yet, its presence in a coal tar sample (SRM 1597a) stresses the importance of expanding the environmental monitoring of PAH isomers with MM 302 Da beyond the 23 isomers currently available.

 

• The thorough investigation of the photoluminescence properties of PASHs containing four benzene rings (molecular mass 234 Da) led to a highly selective method of detection in complex environmental extracts. Data sets consisting of room- temperature absorption spectra, excitation and phosphorescence spectra at 77 K and

4.2 K and low-temperature phosphorescence lifetimes are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC;https://data.gulfresearchinitiative.org/pelagos-symfony/data-discovery). It is possible now to determine parts-per-billion levels of benzo-thiophenes and phenanthro-thiophenes in RPLC fractions with numerous co-eluting fluorescence compounds of unknown chemical nature. The investigated PASHs include benzo[b]naphtho[1,2- b]thiophene, benzo[b]naphtho[2,1-b]thiophene and benzo[b]naphtho[2,3-b]thiophene;