Christian D. Zeigler

Total alkylated polycyclic aromatic hydrocarbon characterization and quantitative comparison of selected ion monitoring versus full scan gas chromatography/mass spectrometry based on spectral deconvolution

Quantitative information of alkylated PAH is frequently used in forensic investigations to characterize petroleum releases and fate in the environment. Interference from a complex matrix often obviates target compound quantitation. Using single ion SIM or a single mass spectral pattern to analyze these homologs should result in either over- or underestimating their concentration. To confirm this hypothesis, a library of C(1)-C(4) alkylated PAH fragmentation patterns were made from automated sequential two-dimensional GC-GC/MS data and the Ion Signature deconvolution software. Based on these patterns, 1D GC/MS data was compared using single ion extraction and one fragmentation pattern per homolog against data obtained from those peaks whose scans met the spectral deconvolution criteria. Significant overestimation occurs when a single ion is used to extract peak signal for C(4)-naphthalene, C(1)-fluorene, and the C(1)- to C(3)-dibenzothiophenes. In contrast, C(2)-naphthalene, C(2)-fluorene, C(3)-phenanthrene, and C(1)-dibenzothiophene were underestimated by >50% when one fragmentation pattern per homolog was used. The Ion Signature deconvolution software makes it easy to interpret mass spectrometry data, especially in complex environmental samples like diesel fuel.

Comprehensive profiling of coal tar and crude oil to obtain mass spectra and retention indices for alkylated PAH shows why current methods err.

Investigators use C(1) to C(4) substituted polycyclic aromatic hydrocarbons (PAH) to assess ecological risk and to track fossil fuels and related pollutants in the environment. To quantify these compounds gas chromatography/mass spectrometry (GC/MS) is used. This work demonstrates single ion monitoring (SIM) or extraction (SIE) of full scan data produces inaccurate and imprecise concentration estimates due to incorrect homologue peak assignments. Profiling of coal tar and crude oil by automated sequential GC-GC/MS provided the retention windows and spectral patterns for each homologue to correctly quantify these compounds. Simultaneous pulsed flame photometric (sulfur-specific) detection differentiated PAH from polycyclic aromatic sulfur heterocycles and their alkylated homologues when they eluted within the same retention windows and had common ions. Differences between SIE and spectral deconvolution of GC/MS data based on multiple fragmentation patterns per homologue ranged from a few percent for C(1) compounds to hundreds of percent for the higher alkylated homologues. Findings show current methods produce poor quality data adversely affecting forensic investigations, risk assessments, and weathering studies.

Toward the accurate analysis of C1-C4 polycyclic aromatic sulfur heterocycles.

Polycyclic aromatic sulfur heterocycles (PASH) are sulfur analogues of polycyclic aromatic hydrocarbons (PAH). Alkylated PAH attract much attention as carcinogens, mutagens, and as diagnostics for environmental forensics. PASH, in contrast, are mostly ignored in the same studies due to the conspicuous absence of gas chromatography/mass spectrometry (GC/MS) retention times and fragmentation patterns. To obtain these data, eight coal tar and crude oils were analyzed by automated sequential GC-GC. Sample components separated based on their interactions with two different stationary phases. Newly developed algorithms deconvolved combinatorially selected ions to identify and quantify PASH in these samples. Simultaneous detection by MS and pulsed flame photometric detectors (PFPD) provided additional selectivity to differentiate PASH from PAH when coelution occurred. A comprehensive library of spectra and retention indices is reported for the C(1)-C(4) two-, three-, and four-ring PASH. Results demonstrate the importance of using multiple fragmentation patterns per homologue (MFPPH) compared to selected ion monitoring (SIM) or extraction (SIE) to identify isomers. Since SIM/SIE analyses dramatically overestimate homologue concentrations, MFPPH should be used to correctly quantify PASH for bioavailability, weathering, and liability studies.

Mass Spectra and Retention Indexes for Polycyclic Aromatic Sulfur Heterocycles and Some Alkylated Analogs

Polycyclic aromatic sulfur heterocycles (PASH) are ubiquitous in fossil fuels and pose risk to the environment due to their toxicity. Some PASH, resistant to degradation in the environment, are used to differentiate pollutant source and weathering. Although retention data exist for some PASH, few mass spectra are available, so misidentification often occurs between isomers in the same family. In this study, the retention behavior of 119 PASH on 14%-cyanopropyl/86%-polydimethylsiloxane (DB-1701ms), trifluoropropylmethylpolysiloxane (Rtx-200ms), 5%-phenyl/95%-dimethyl (Rxi-5ms), and 50%-diphenyl/50%-dimethyl (Rxi-17Sil-ms) are reported along with their mass spectra. This data is guiding on-going research aimed at identifying PASH in coal tar by multidimensional GC-GC/MS for compounds where standards are not available.

A more accurate analysis of alkylated PAH and PASH and its implications in environmental forensics

The accurate measurement of polycyclic aromatic hydrocarbons (PAH), polycyclic aromatic sulfur heterocycles (PASH), and their alkylated homologues is essential at all levels of risk assessment and remedial decision-making. In the field of environmental forensics, diagnostic ratios of these compounds are used to delineate fossil fuel-based sources from one another and to assess the degree of weathering occurring on-site. Fresh and weathered coal tar and crude oil samples from different locations were analysed by gas chromatography/mass spectrometry. The same files were analysed by selected ion extraction of one-ion and two-ion signals from full-scan data and compared to a new data analysis method using spectral information from homologous isomers. Findings showed that using too few ions produced false positives and concentrations much higher than those found using the homologous isomer spectral method, which adversely affected the corresponding diagnostic ratios used by forensic scientists.

New spectral deconvolution algorithms for the analysis of polycyclic aromatic hydrocarbons and sulfur heterocycles by comprehensive two-dimensional gas chromatography-quadrupole mass spectrometery.

New mass spectral deconvolution algorithms have been developed for comprehensive two-dimensional gas chromatography/quadrupole mass spectrometry (GC × GC/qMS). This paper reports the first use of spectral deconvolution of full scan quadrupole GC × GC/MS data for the quantitative analysis of polycyclic aromatic hydrocarbons (PAH) and polycyclic aromatic sulfur heterocycles (PASH) in coal tar-contaminated soil. A method employing four ions per isomer and multiple fragmentation patterns per alkylated homologue (MFPPH) is used to quantify target compounds. These results are in good agreement with GC/MS concentrations, and an examination of method precision, accuracy, selectivity, and sensitivity is discussed. MFPPH and SIM/1-ion concentration differences are also examined.

A Biosurfactant/Polystyrene Polymer Partition System for Remediating Coal Tar-Contaminated Sediment

ABSTRACT A sustainable, green chemistry process is proposed for the cleanup of coal tar impacted sediment in under 2 hr. A mixture of proteins and polypeptides, extracted from corn gluten meal and hemp, when mixed with sediment and polystyrene foam pellets (PFPs), serves to mobilize tar, which sorbs onto PFP. Since the sorbent floats, coal tar is easily extracted from the agitation vessel. An empirically derived 4-dimensional surface response model accurately predicts removal rates of the tar and operational costs of the system under various experimental conditions. At optimum relative to cost, 81% of the two to six ring polycyclic aromatic hydrocarbons (PAHs) and 73% of the total tar mass are removed despite high sediment organic carbon content (16.4%) and silty fines (∼85%). Multiple PFP extractions (n = 2) of the same sediment/biosurfactant mixture yielded 94% extraction of PAH. Scanning electron microscope images illustrate free-phase tar (globule) sorption onto the foam. A field pilot was conducted in which 25 kg of sediment was processed. Results were in excellent agreement with both lab (10 g) experiments and model predictions. The process is considered sustainable and green because the active ingredients are derived from renewable crop materials, recycled polystyrene is used, and the biosurfactant is recyclable which reduces water demand and treatment costs, with the recovered tar used as fuel and sediment as beneficial reuse material.