Fixing False Negatives, Using 2DGC-TOFMS to Correctly Identify Ignitable Liquid Residues (ILRs) in Wildfire Investigations – Pittcon 2019

Fixing False Negatives, Using 2DGC-TOFMS to Correctly Identify Ignitable Liquid Residues (ILRs) in Wildfire Investigations from Chemistry Matters Inc.

During the Pittcon 2019 conference in Philadelphia, Pennsylvania, Dr. Court Sandau of Chemistry Matters Inc. presented on the fundamentals of using two-dimensional gas chromatography to correctly identify ignitable liquid residues in wildfire investigations.

Wildfires continue to grow in frequency and intensity. Over 80% of wildfires are human caused . Over 20%  of those are attributed to acts of arson. The ability to detect ILRs and accelerants in wildfire debris samples can be very problematic compared to structural fire debris samples.

Wildfires versus structural fires

Forensic methods used in the analysis of wildfire debris are complicated by the presence of natural interferences. Wildfires provide exceptionally difficult matrices compared to structural fires due to the following:

1. ILRs are present at lower concentrations;
2. ILRs are more dispersed;
3. natural compounds are present at very high concentrations;
4. structural similarity of natural compounds to ILR compounds; and
5. matrix combustion forms other interfering compounds.

The resolving power of comprehensive two-dimensional gas chromatography (GCxGC, 2DGC) combined with the sensitivity of a TOF-MS permits superior separation and detection of ILRs compared to conventional gas chromatography (1DGC). The high abundance of natural interferences dwarfs the ILR compounds in size and will mask their detection using conventional 1DGC. As arsonous wildfires can ignite with very low volumes of accelerants, better detection limits are required in order to find and identify ILRs in wildfire debris samples.

Case samples analyzed on both 1DGC and 2DGC showed re-analysis by 2DGC changed 7% of negative samples to positive for ILR, and 22% went from tentative to positive for ILR. Inspection of the Stauffer compounds shows some groups are more useful for ILR identification than others. The Three Musketeers Group was ubiquitous, while the Twin Towers and Five Fingers Groups were non-detects by 1DGC but present in up to 90% of positive samples by 2DGC. In addition, the use of 2DGC allows expansion of the targeted list of compounds to expand to all compounds present in gasoline which increase to over 2000 compounds, potentially allowing for gasoline fingerprinting.

Dr. Sandau presents on 2DGC at Pittcon 2019