Comparison Sample
Definition
A sample of the same substrate type collected from an unburned area of the same room or adjacent space. Provides the substrate background chromatogram against which fire debris GC-MS data is compared in the background subtraction methodology.
- Field
- Accelerant detection and fire debris analysis
- Source
- Same substrate type from an unburned area nearby
- Analysis method
- GC-MS, matched conditions to the debris sample
- Function
- Background subtraction reference
Common questions
How is this different from the comparison control sample used at the substrate-interferent stage?+
They serve the same underlying purpose, background subtraction, but this term is used in the context of scene-side accelerant detection alongside canine and PID screening, while the substrate-interferent context refers to the same practice at the laboratory GC-MS interpretation stage; both require matched, unburned, same-substrate material.
Why must the comparison sample be run under identical GC-MS conditions?+
Retention times and fragmentation patterns shift with instrument parameters such as oven ramp rate and column type, so any difference in run conditions between the debris sample and the comparison sample would make the background subtraction unreliable.
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