Simplified Quantitation of C6-C14 Aromatics in Detailed Hydrocarbon Analysis of Gasolines by Simultaneous Dual-Detection GCxGC-TOFMS and FID

PMI (particulate matter index) is an important measure for the performance and environmental impact of spark-ignition fuels like gasoline. In general, while higher aromatics content in gasolines has been correlated with higher PMI values, traditional fuel quality measures do not take into account the speciation and quantitation of individual C6-C14 isomers beyond benzene, toluene, xylenes, ethylbenzene, and a few naphthalenes. Single-dimension gas chromatography (GC) analyses are slow and often challenged by coelutions with other hydrocarbon types. Even the addition of mass spectrometry, which allows for more specificity for quantitation of these aromatic compounds, can produce results that are biased by matrix interferences. Comprehensive two-dimensional gas chromatography (GCxGC) resolves these interferences by pulling aromatic species into separate, easy-to-interpret elution regions, providing more accurate quantitative information with shorter analytical runtimes. Simultaneous dual-detection from time-of-flight mass spectrometry (TOFMS) and flame ionization detection (FID) with properly regulated split throughout the GC temperature program allows the TOFMS to provide identification of additional lower-level aromatic isomer species that can have a higher effect on PMI in the same run that the FID returns simple area % based quantitation. Additional semi-quantitative calibrations can be applied based on curves generated from characteristic mass fragments generated by the TOFMS to confirm FID area % response values. This presentation explores a variety of column configurations and software workflows developed for application of GCxGC-TOFMS/FID for improving the quantitation of C6-C14 aromatics in gasolines.