The Compare Feature of ChromaTOF —Its Use in Forensic Chemistry to Assist with the Determination of the Cause of Death

Importance of the Topic

The ability to rapidly and reliably link complex biological extracts to suspected toxicants is critical in forensic investigations of accidental poisoning and suspected suicide. Targeted comparison of chromatographic profiles reduces interpretation time and improves evidentiary value when matrices are complex, metabolites or dilution obscure direct matches, and rapid decisions are required.

Objectives and Study Overview

This application note demonstrates the use of the ChromaTOF "Compare" feature (LECO) in a real forensic case: comparison of an industrial cleaner (neat product) with a stomach extract from a deceased individual to determine whether ingestion of the cleaner caused the death. The goal was to use automated peak finding, spectral deconvolution, and a tailored reference list to rapidly identify marker compounds from the cleaner in the biological matrix.

Methodology and Data Processing

The approach combined gas chromatography with time-of-flight mass spectrometry (GC-TOFMS) and software-driven workflows. Key processing steps were automated peak detection, spectral deconvolution to resolve overlapping signals, and comparison against a limited Reference Table containing selected marker compounds from the cleaner. The Compare routine reports matches, similarity scores, and whether detected levels met a pre-set tolerance relative to the neat material.

Instrumentation

Agilent 6890N GC with a 30 m x 0.25 mm x 0.25 µm Rtx-CLPesticides column; oven program 60 °C (2 min), ramp 12 °C/min to 300 °C (2 min); inlet 200 °C, 1 µL splitless injection, helium carrier at 1 mL/min, transfer line 220 °C, total run 24 min. LECO Pegasus III GC-TOFMS operated with electron ionization (70 eV), mass range 45–450 u, acquisition at 20 spectra/s, source at 200 °C. Data were processed using LECO ChromaTOF for automated peak find, deconvolution and the Compare algorithm.

Main Results and Discussion

Total ion chromatograms (TICs) for the cleaner and the stomach extract were complex and not trivially comparable by eye. To increase specificity, a Reference Table of 12 marker compounds characteristic of the cleaner was created from the cleaner sample's deconvoluted peak table. The Compare method searched the stomach extract for these 12 markers. Results showed that 11 of the 12 marker compounds were detected in the stomach extract at levels meeting the software’s match tolerance (set to flag matches when stomach levels were ≥1% of neat cleaner). Naphthalene was detected but assigned "Out of Tolerance," indicating its abundance in the stomach extract was below the 1% threshold. Similarity scores and unique diagnostic mass ions aided compound identification despite matrix complexity and potential metabolic alteration.

The study illustrates several practical factors: (1) targeted lists of marker analytes simplify comparison in highly complex matrices; (2) spectral deconvolution can reveal compounds masked in TICs; (3) concentration thresholds must be chosen with awareness of dilution, metabolism, and differential extraction efficiency; and (4) unique mass ions and library similarity improve confidence but do not replace orthogonal confirmation if legal/forensic standards require it.

Benefits and Practical Applications

• Speed: Compare performs automated, peak-by-peak and spectrum-by-spectrum searches, enabling rapid screening of complex samples.
• Specificity: Limiting the Reference Table to a small set of distinctive markers increases detection sensitivity in complex matrices.
• Versatility: Useful across forensic contexts (poisoning cases) and non-forensic applications (e.g., pesticide cocktails in produce, quality control of formulations).
• Evidence support: Provides strong confirmatory evidence when multiple characteristic markers are found in a biological matrix.

Future Trends and Opportunities

• Integration with higher-resolution MS and MS/MS to increase selectivity and confirmatory power for metabolites and isomers.
• Improved deconvolution algorithms and machine-learning-driven spectral matching to better handle low-abundance components and coelution.
• Expansion of curated reference libraries with retention indices and marker ion lists tailored for forensic contaminants and formulation components.
• Automated workflows that combine targeted Compare searches with quantitative validation and reporting suitable for forensic chain-of-custody requirements.
• Portable and field-deployable GC-TOFMS instruments enabling on-site screening in emergency situations.

Conclusion

The ChromaTOF Compare feature demonstrated an efficient targeted-screening workflow that successfully linked the cleaner formulation to components found in a stomach extract, supporting the conclusion that ingestion of the cleaner contributed to the death. By focusing on a limited set of marker compounds and leveraging deconvolution and unique mass ions, the method provided robust corroborative evidence despite matrix complexity and dilution effects. Users should complement such targeted comparisons with appropriate confirmatory analyses when required by forensic standards.

References

LECO Corporation. The Compare Feature of ChromaTOF — Its Use in Forensic Chemistry to Assist with the Determination of the Cause of Death. LECO Corporation, St. Joseph, MI; Form No. 203-821-256, 2008.