A Complete Library of Retention Indices and Mass Spectra of C1 to C4 PAH and PASH Enables a Critical Evaluation of Environmental Analytics.
Abstract: Polycyclic aromatic hydrocarbons (PAH), polycyclic aromatic sulfur
heterocycles (PASH), and their C1 to C4
substituted analogs are ubiquitous in fossil fuels and pose risk to the environment due to
their toxicity. These compounds are also used to identify the source and track the fate of
fossil fuels and related pollutants in the environment. Investigators employ gas
chromatography/mass ... read morespectrometry (GC/MS) to quantify PAH and PASH. Unfortunately,
convoluted mass spectra are unavoidable in complex samples. To circumvent this limitation,
investigators use selected ion monitoring (SIM) or extraction (SIE). In these modes, signal
from only the PAC molecular ion is acquired by the instrument (SIM) or extracted from full
scan data (SIE). Identification is based on peak response within a predefined retention
window. This work demonstrates SIM/SIE analyses result in faulty concentration estimates
due to incorrect assignment of peaks within each homolog. Since few alkylated PAC
fragmentation patterns are known, automated sequential GC-GC/MS profiling of coal tar and
crude oil provided homolog-specific spectra and defined the retention windows in which
these compounds elute. Simultaneous pulsed flame photometric (sulfur-specific) detection
differentiated PAH, PASH, and their alkylated homologs when these compounds (co)eluted
within the retention windows. The retention behavior of 119 PASH standard compounds on four
stationary phases is reported along with their mass spectra, and was used to guide
multidimensional GC-GC/MS for compounds where standards were not available. A comprehensive
library of spectra and retention indices are reported for the C1 to
C4 2-, 3-, and 4-ring PAH and PASH. This library enabled a critical
evaluation of SIM/SIE analyses. Differences between SIM/SIE and the multiple fragmentation
patterns per homolog (MFPPH) approach ranged from a few percent for C1 compounds to as much
as hundreds of percent for the higher alkylated homologs. Incorrect quantification has
profound impacts on fate, transport, risk assessment, bioavailability, and weathering
studies due to the propensity of PAC to resist natural or active remediation. The data
needed for the MFPPH approach, provided herein, serves as the basis for accurate and
defensible assessment of PAC concentrations, which will improve environmental forensics and
toxicological studies in the future.
Thesis (Ph.D.)--Tufts University, 2012.
Submitted to the Dept. of Chemistry.
Advisor: Albert Robbat.
Committee: Jonathan Kenny, Michele Schantz, and David Walt.
Keyword: Chemistry.read less