CNT-SPME Yields High Selectivity of Gasoline in GC–MS Analysis of Fire Debris

A new study published in the Journal of Chromatography A proposes a novel extraction technique prior to analysis by gas chromatography coupled to mass spectrometry (GC–MS) for the purpose of determining gasoline residue in simulated fire debris samples (1).

Gasoline Can in front of a Fire, Fire Hazard, Burning Hazard | Image Credit: © Alissa Yarbrough - stock.adobe.com

Co-authored by Ting-Yu Huang and Jorn (Chi Chung) Yu of the Department of Forensic Science in the College of Criminal Justice at Sam Houston State University in Huntsville, Texas, USA, the study experimented with a carbon nanotube-assisted solid-phase microextraction (CNT-SPME) fiber prepared by a sequential coating of polydopamine, epoxy, and carbon nanotubes (CNT) on a stainless-steel wire.

CNTs are formed by rolling one or more graphite sheets into a cylinder, making either single- or multi-walled carbon nanotubes (SWCNT or MWCNT, respectively). The high ratio of µm-scaled length to nm-scaled diameter in these apparatus provides a large surface area and other outstanding structure-dependent properties such as tensile strength, thermal stability, and mechanical robustness. CNTs have been widely used as adsorbents in biochemical, drug, environmental, food, and pesticide analysis, and CNT-coated SPME fibers specifically have demonstrated a capability to extract aromatic compounds.

Extracting gasoline and its major aromatic groups including xylenes, alkylbenzenes, indanes, and naphthalenes is of interest in fire debris analysis with more than 52,000 intentionally set fires having been reported in the United States annually between 2014 and 2018, according to the National Fire Protection Association. In their report, ignitable liquids accounted for 37% of the 400 annual civilian deaths, 22% of the 950 injuries, and 19% of the $815 million in direct property damage during that time, with readily available gasoline being the most widely used liquid by arsonists.

The use of activated charcoal strips as extraction media for gasoline residue is described in the American Society for Testing and Materials (ASTM) E1412-19 and ASTM E1618-19, but there has been a trend of replacing the activated charcoal with SPME, as can be found in ASTM E2154-15a. The advantages of SPME include being a fast, non-destructive, and solvent-free method that is readily simplified and automated, and the SPME fiber can be reused unlike the activated charcoal strip. Employing a CNT coating to SPME fiber in this application can cut down on some of the drawbacks of SPME, including significant discrimination against compounds with different volatility.

Results measured against a 100 µm commercial polydimethylsiloxane (PDMS) SPME fiber and an activated charcoal strip provided validation for the proposal of the CNT-SPME method. Average relative standard deviations and accuracies for all concentration ranges in this experiment were lower than 15%, with the relative recovery of the CNT-SPME fiber for all aromatic groups ranging from 28±3% to 59±2%. Also, this fiber showed a particular higher selectivity for naphthalenes in gasoline, using an experimental pulsed thermal desorption process. The researchers believe that CNT-SPME can be a viable approach not only for the identification of gasoline residue in fires, but that of other ignitable liquids as well.

Reference

(1) Huang, T.-Y.; Yu, J. Carbon nanotubes-assisted solid-phase microextraction for the extraction of gasoline in fire debris samples. J Chromatogr. A 2023, 1701, 464063. DOI: 10.1016/j.chroma.2023.464063