Decomposition Analysis Using Differing Data Processing Methods to Identify Volatile Organic Compounds

Importance of the Topic

Aquatic decomposition produces a distinct volatile signature that can guide forensic water sampling and postmortem interval estimates.
Understanding these VOC profiles enhances crime scene analysis in submerged contexts, filling a critical gap in forensic chemistry.

Objectives and Study Overview

The study aims to characterize volatile organic compounds evolving from submerged animal tissue and to evaluate different data processing methods for GC×GC-TOFMS outputs to optimize compound identification and longitudinal tracking.
Nine pork belly samples and three water controls were submerged at 32°C, 22°C, and 5°C over a 12-day period, with periodic headspace sampling.

Methodology

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) measured the headspace above water-filled mason jars containing decomposing pork belly.
Sampling schedule: daily collections for days 0–3, then every three days until day 12, with 5 mL headspace withdrawns.
Data processing approaches:

• ChromaTOF quant mass integration on single chromatograms
• ChromaTOF Tile with Fisher Ratio for class discrimination
• ChromaTOF Tile with Coefficient of Variance and Fold Change for trend analysis
• ChromaTOF Sync 2D for alignment of co-eluting peaks

Peak tables were curated, exported to Excel, and cross-referenced with literature to categorize compounds as confirmed or novel.

Instrumentation

The analytical platform comprised a GC×GC-TOFMS system equipped with a quad-jet dual-stage cryogenic modulator and a secondary oven, enabling high-resolution separation of complex odor profiles.

Main Results and Discussion

Temperature significantly influenced VOC emergence: 32°C samples exhibited greater compound diversity and earlier detection of sulfur- and indole-derived volatiles.
Sync 2D processing, while more time-consuming, recovered a larger number of compounds at later time points and reflected raw peak trends accurately.
Coefficient of Variance and Fold Change approaches delivered clear class separation in principal component analyses, effectively distinguishing 32°C profiles from lower temperatures.
Fisher Ratio prioritized a concise subset of highly discriminating compounds, enabling rapid differentiation with minimal computational overhead.

Benefits and Practical Applications

• Provides a decision framework for selecting data-processing workflows based on forensic versus research priorities (trend monitoring vs. quick screening).
• Identifies key VOC markers for submerged decomposition, informing water‐sampling protocols at aquatic crime scenes.
• Offers longitudinal tracking methodologies that can enhance postmortem interval estimation in submerged scenarios.

Future Trends and Opportunities

• Development of a comprehensive database of submerged decomposition VOCs for forensic reference and automated searches.
• Extension of experiments to full cadaver models and varied water chemistries to validate and generalize findings.
• Integration of portable or field-deployable GC×GC-TOFMS systems for on-site analysis.
• Evaluation of advanced data processing, including machine learning algorithms, for automated compound identification and pattern recognition.

Conclusion

This work demonstrates that GC×GC-TOFMS, coupled with tailored data-processing workflows, can reliably detect and differentiate VOCs from submerged decomposition.
Sync 2D is optimal for detailed longitudinal studies, Coefficient of Variance and Fold Change excel at class discrimination, and Fisher Ratio offers efficient compound prioritization for rapid forensic screening.

References

(1) Stadler S. et al. Characterization of volatile organic compounds from human analogue decomposition using thermal desorption coupled to comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry. Analytical Chemistry 2013, 85(2):998–1005.
(2) Ho J. et al. Identifying VOCs from human remains detectable in water using comprehensive two-dimensional gas chromatography. Forensic Chemistry 2024, 38:100561.
(3) Armstrong P. et al. Establishing the volatile profile of pig carcasses as analogues for human decomposition during the early postmortem period. Heliyon 2016, 2(2):e00070.