Tracking the Chemical Shift from Life to Death: Advanced VOC Analysis with GC×GC-TOF-MS

The transition from a living person’s scent (ante-mortem odor) to decomposition odor (post-mortem odor) is crucial in search and rescue operations. This odor determines whether search-and-rescue (SAR) dogs (trained for live scent) or human remains detection (HRD) dogs (trained for decomposition scent) should be deployed. This scent change likely occurs during the fresh stage of decomposition, but its timing, and the persistence of ante-mortem odor compounds, remain poorly understood.

A recent study investigated early post-mortem volatile organic compounds (VOCs) from human donors in an outdoor environment. Using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF-MS)—a first for early post-mortem human VOC profiling outdoors—the research aims to track VOC changes, pinpoint the ante-mortem to post-mortem odor transition, and improve scent detection dog training strategies. LCGC International spoke to Darshil Patel, of the University of Windsor and lead author of the article published in Forensic Science International: Synergy (1), about his team’s findings.

Why was two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOF-MS) chosen over traditional gas chromatography-mass spectrometry (GC-MS) methods for analyzing early post-mortem volatile organic compounds (VOCs) in this study, and what specific advantages did it provide in handling complex decomposition profiles?

Decomposition odor profiles contain a complex mixture of VOCs that belong to diverse chemical functional classes and occur across a broad concentration range. Conventional one-dimensional GC-MS does not possess sufficient resolving power to capture the complete chemical make-up of this mixture. Comprehensive GC×GC-TOF-MS addresses this limitation. In GC×GC, a modulator periodically focuses analytes exiting the first-dimension column and transfers them onto a second column coated with a stationary phase that offers a different separation mechanism. This configuration markedly enhances selectivity, sensitivity, and most critically peak capacity, defined as the maximum number of components that can be satisfactorily separated within a chromatographic system. The result is a far more detailed and representative chemical fingerprint of the decomposition odor profile than is achievable with standard GC-MS.

Can you elaborate on the challenges encountered when interpreting VOC class abundance from shroud versus aluminum hood sampling methods, and how these might impact future standardization in VOC analysis?

One of the biggest challenges is the lack of data from shroud or body bag samples, especially when the donor is still in the fresh stage. Most work with cadavers has been done outdoors using an aluminum hood to create the headspace, so we already have more data and a better general understanding for that setup. With a shroud or body bag the situation is quite different. I have worked in morgues in Australia and Canada, and the bags or shrouds they use are made from different materials. The way the bodies are transported to the morgue also varies. All these factors influence how many volatiles we recover and how the VOC classes line up.

To move toward standardization, we first need more research that looks at how volatiles behave in the different headspaces created by a shroud versus an aluminum hood. For indoor trials we could test several common shroud or body bag materials, measure how each one affects compound recovery, and then settle on a single bag type or at least a short list that can serve as the standard for future VOC analysis.

What were some limitations or considerations in using normalized peak areas to track the persistence and transition of VOCs, particularly ante-mortem ones, in different environments (morgue vs. outdoor)?

This point really builds on the previous question. We still have only a limited understanding of how individual volatiles behave in different headspaces, so there are several practical considerations when we rely on normalized peak areas. In our study, we kept the sampling time identical in the morgue and outdoor settings so the two datasets would be directly comparable. That choice helps with side-by-side comparisons, but the sample collection period can miss or under-represent certain compounds, especially those released for only a short period right after death. The issue is more pronounced indoors, where decomposition is just beginning and VOCs can be present in lower concentrations. Under those conditions the sample collection period might not be long enough to pre-concentrate the VOCs in the headspace.

How do environmental factors such as ultraviolet (UV) radiation, temperature, and ozone exposure influence the persistence of ante-mortem VOCs in outdoor decomposition scenarios?

Skin is a major source of ante-mortem VOCs that is present during the fresh stage of decomposition. Outdoors, UV can photochemically change skin lipids, temperature drives volatility, and ozone can oxidize surface compounds and generate new VOCs. We have not yet quantified how strongly each factor shifts the profile, and that is an area for future work.

Based on your findings, how would you describe the chemical and temporal boundary between ante-mortem and post-mortem scent? Is there a definitive marker or is it a gradual shift?

The boundary between ante-mortem and post-mortem scent is best described as a continuum that changes with each stage of decomposition. In the early post-mortem or fresh stage, the chemical profile is highly variable; many ante-mortem volatiles begin to decline while VOCs related to decomposition odor appear, so the transition is gradual and no single compound serves as a universal marker. As the remains progress into bloat or active decay, soft tissues start to distend and break down, typical decomposition volatiles such as sulfur- and nitrogen-containing compounds rise sharply, and the overall profile shifts decisively toward a post-mortem odor, making the chemical boundary much definitive. Human cadavers also undergo differential decomposition, where different body regions advance at different rates, producing mixed chemical signals that extend the period of gradual transition until most tissues reach bloat or active decay. In short, the antemortem to post-mortem shift is gradual during the fresh stage but becomes far more pronounced once bloat and active decay set in, and there is no single definitive marker; instead, stage-specific compound patterns indicate where the remains lie along the decomposition timeline.

Nitrogen-containing compounds were dominant in early decomposition. What do their dynamics tell us about enzymatic versus microbial contributions to early postmortem odor profiles?

VOCs can arise through several pathways. In the first hours after death, the dominance of nitrogen-containing volatiles points to enzyme activity that starts almost immediately. Intracellular proteases and other hydrolases break down proteins into free amino acids, and some of these such as lysine and ornithine decarboxylate to form volatile amines, giving an endogenous, enzyme-driven source of nitrogen compounds. Within the next several hours, microorganisms on the skin, in the gut, and in the airways begin to proliferate; equipped with their own decarboxylases and deaminases, they act on the same amino-acid pool and release a second wave of nitrogen volatiles, including classic tryptophan catabolites such as indole. The exact biochemical routes and the relative contribution of each process are not yet fully mapped, and it is likely that multiple mechanisms operate at the same time. Further investigation is needed to disentangle their kinetics and individual impact on the early post-mortem odor profile.

How do your results inform the hypothesis about the presence and role of a dehalogenating microbiome in shaping early post-mortem VOC signatures?

Our results suggest that halogenated compounds detected in early post-mortem samples may originate through more than one pathway. Traditionally, we have attributed these volatiles to ante-mortem exposure—medications, environmental contact, or industrial contaminants absorbed during life. However, the data also align with the hypothesis that a de-halogenating microbiome could transform halogenated substrates after death and release them as volatile metabolites. This possibility broadens the scope of inquiry: rather than viewing halogenated VOCs solely as residual markers of lifetime exposure, we now have grounds to explore a microbially mediated, post-mortem source. Confirming such activity would refine our interpretation of early decomposition signatures and offer new insight into microbial roles in VOC formation.

Given your observations, what would be the ideal timeframe for deploying search-and-rescue (SAR) vs.human remains detection (HRD) dogs in post-disaster environments to maximize detection reliability?

If the condition of victims (dead or alive) is unknown, it is important to deploy both SAR and HRD dog units for up to the first 96 hours. During this early post-mortem period, VOC profiles change markedly from hour to hour and day to day, so using both types of dogs maximizes the likelihood of detection and recovery. In addition, external factors such as local environment, temperature, humidity, and rainfall can influence VOC composition; understanding these conditions can further guide decisions on when and where to assign SAR versus HRD teams.

What are the implications of your findings for the design and chemical accuracy of synthetic training aids for SAR and HRD dogs? What geographical or seasonal variables do you see as most critical for future VOC profiling studies, and how might they influence global SAR/HRD deployment strategies?

It is a challenging aspect and with advancements in the field of volatilomics, these synthetic training aids would have evolve as we discover new compounds and chemical classes especially ones that are identified to be significant or are discriminatory amongst the human and other species. I truly understand the challenge in changing formulations but with the advancements in the omics field or volatilomics, we have discovered variety of compounds been identified through skin, sweat, breath and various other bodily fluids and same could be said for decomposition odor when studied in different environments and with advance techniques such as two-dimensional gas chromatography techniques or some other analytical techniques.

In terms of geographical or seasonal variables understanding the impact of cold/freezing weather and rain will be most critical. Apart from these, I also think understanding the intra and inter-day differences on the VOC profiles would be critical as there are fluctuations in temperature, humidity etc. with the day as well. Further scavenger studies which also currently being conducted in various geographical regions would be critical.

Is there anything else about your research that you would like our readers to know?

This study of how odor transitions during the early post-mortem period is still in its initial phase. We have only begun to explore the first hours and days after death. Replicating the work, applying the same perspective, and conducting trials in a range of environments will deepen our understanding and ultimately help us deploy SAR and HRD dogs more effectively in real search-and-rescue scenarios.

References

1. Patel, D.; Burr, W. S.; Daoust, B. et al. Identifying the Transition from Ante-Mortem to Post-Mortem Odor in Cadavers in an Outdoor Environment. Forensic Sci. Int. Synerg. 2025, 11, 100616. DOI: 10.1016/j.fsisyn.2025.100616