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

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... were analysed by gas chromatography/mass spectrometry. The same files were analysed by selected ion extraction of one-ion and twoion 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.