Cross-Contamination of Ignitable Liquid Residues on Wildfire Debris—Detection and Characterization in Matrices Commonly Encountered at Wildfire Scenes

Abstract

Ignitable liquid residue (ILR) samples play an important role in fire investigations. Similar to other types of forensic evidence, maintaining sample integrity depends on the prevention of cross-contamination during both storage and transport. This study examines cross-contamination in ILR samples on various sample matrices (gravel, soil, wood). After inducing leaks in a controlled environment, sample analysis by GC×GC-ToF MS allowed for sensitive detection and in-depth characterization of cross-contamination processes. The potential for false positive identification of ILR is notably present due to cross-contamination. Compound transmission for a mid-range ILR (gasoline), for instance, was detectable after a 1 h exposure, with a complete profile transfer occurring after 8 h regardless of the matrix type. Visual comparisons and uptake rate calculations further confirmed matrix interaction effects taking place in the form of inherent native compound interference and adsorbate–adsorbate interaction during transmission and extraction processes for soil and wood matrices. Chemometric analysis highlighted the advantage of employing statistical analysis when investigating samples under matrix interactions by identifying several statistically significant compounds for reliably differentiating cross-contamination from background and simulated positive samples in different volatility ranges and compound classes. Untargeted analysis tentatively identified three additional compounds of interest within compound classes not currently investigated in routine analysis. The resulting classification between background, contaminated, and simulated positive samples showed no potential for false positive ILR identification and improved false negative errors, as evidenced by classification confidences progressing from 88% for targeted and 93% for untargeted to 95% for a diagnostic ratio analysis of three ratios deployed in tandem.

Cross-Contamination of Ignitable Liquid Residues on Wildfire Debris—Effects of Packaging and Storage on Detection and Characterization

“…Standards and reagents were prepared as described by Boegelsack et al [21]. All solvents [benzene (99.9%), carbon disulfide (99.9%), dichloromethane (99.9%), methanol (99.9%), and toluene (99.9%)], as well as individual standards for naphthalene-d 8 (AC174960010) and ethylbenzene-d 10 (AC321360010), were obtained from Fisher Scientific (Ottawa, ON, Canada).…”

“…The compounds had a concentration of 500 ng/mL each. The gasoline sample (87% octane) is the same sample as used in Boegelsack et al [21], purchased locally in Calgary, AB, Canada. Three reference samples were used in this study: a matrix sample, a contaminated matrix sample, and a spiked matrix sample.…”

“…The experimental design was completed in two phases, using a similar approach to an earlier study by Boegelsack et al [21]. Phase one was conducted with a two-piece laboratory glovebox (Model 818-GBB-Plas-Labs, Lansing, MI, USA), sealed with stainless steel clamps to form an air-and water-tight barrier, at room temperature to compare the effectiveness of packaging types to mitigate uptake from an atmosphere impacted by an ignitable liquid.…”

“…Chemometric analysis has been applied to ILR research-most frequently regarding detection and classification [13,20]-but is not commonly utilized in the context of sample integrity. GC×GC coupled with chemometric analysis showed promise in the detection and characterization of cross-contamination under matrix interference [21], with evaluation of false positive and false negative errors, indicating the presence of cross-contamination with confidence. In addition to matrix interaction, the increased layer of complexity that different packaging types and storage methods represent for ILR interpretation with advanced chromatographic separation is yet to be investigated.…”

“…This study continues to apply the established analytical workflow [19,22] and data analysis approach [21,22] described previously to evaluate packaging methods currently employed for fire debris. Charred wood chips allow for an investigation of a single competing matrix commonly encountered in wildfire debris [15,19], while excluding the additional complications from microbiome changes in soil [16,21,23,24]. This study aims to evaluate common packaging practices currently employed in wildfire investigations to advise on best practices combining practicality and preservation of sample integrity.…”