Modern Instrumental Limits of Identification of Ignitable Liquids in Forensic Fire Debris Analysis

Abstract

Forensic fire debris analysis is an important part of fire investigation, and gas chromatographymass spectrometry (GC-MS) is the accepted standard for detection of ignitable liquids in fire debris. While GC-MS is the dominant technique, comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) is gaining popularity. Despite the broad use of these techniques, their sensitivities are poorly characterized for petroleum-based ignitable liquids. Accordingly, we explored the limit of identification (LOI) using the protocols currently applied in accredited forensic labs for two 75% evaporated gasolines and a 25% evaporated diesel as both neat samples and in the presence of interfering pyrolysate typical of fire debris. GC-MSD (mass selective detector (MS)), GC-TOF (time-of-flight (MS)), and GC×GC-TOF were evaluated under matched conditions to determine the volume of ignitable liquid required on-column for correct identification by three experienced forensic examiners performing chromatographic interpretation in accordance with ASTM E1618-14. GC-MSD provided LOIs of~0.6 pL on-column for both neat gasolines, and~12.5 pL on-column for neat diesel. In the presence of pyrolysate, the gasoline LOIs increased to~6.2 pL on-column, while diesel could not be correctly identified at the concentrations tested. For the neat dilutions, GC-TOF generally provided 2× better sensitivity over GC-MSD, while GC×GC-TOF generally resulted in 10× better sensitivity over GC-MSD. In the presence of pyrolysate, GC-TOF was generally equivalent to GC-MSD, while GC×GC-TOF continued to show 10× greater sensitivity relative to GC-MSD. Our findings demonstrate the superior sensitivity of GC×GC-TOF and provide an important approach for interlaboratory benchmarking of modern instrumental performance in fire debris analysis.

Comprehensive Two-Dimensional Gas Chromatography Advances in Technology and Applications: Biennial Update

“…Thus, GC×GC represents a potent analytical tool that enables the identification of key compounds superimposed on a complicated background, with a simple image-based result. Among the main samples investigated were human remains, − blood, , nerve agents, and environmental crimes, such as spills , and fires. , …”

“…Environmental crimes, such as spills and fires were investigated in different studies, using GC×GC−MS. The technique’s high sensitivity enables the reliable identification of compounds in ignitable liquids after pyrolysis and diesel oil spilled in water from marine environments.…”

“…Among the main samples investigated were human remains, 234−237 blood, 238,239 nerve agents, 240 and environmental crimes, such as spills 153,155 and fires. 241,242 The odor profile of human remains, blood, and its analogues has been studied, mainly, to develop strategies to aid detection dog training or to support their evidence. Cuzuel and coworkers 236,237 used GC×GC to investigate human hand odor, developing optimized methods to obtain a reliable chemical profile and outline strategies to match the results with the person's identity.…”

Advances in Fire Debris Analysis

“…Gasoline residues were detected from bodies burned with the aid of the liquid, and not detected from samples burned without the aid of the liquid or from empty body bag controls. Comprehensive gas chromatography, coupled with time-of-flight mass spectrometry, was shown by Abel and coworkers to provide lower limits of identification by an order of magnitude, relative to GC-MS identification performed by trained analysts for neat 75% evaporated gasoline and 25% evaporated diesel samples [5]. The limits of identification for gasoline were determined to be approximately 6.2 pL on-column for both the neat gasoline and samples containing pyrolysate interferences.…”