Substrate Interferent
Definition
A pyrolysis product from building or furnishing material that produces a GC-MS chromatographic pattern overlapping with or resembling an ignitable liquid category under ASTM E1618. Examples: polypropylene carpet backing, polyurethane foam, asphalt shingles, PVC flooring plasticisers.
- Field
- Fire debris analysis, GC-MS
- Standard
- ASTM E1618
- Origin
- Pyrolysis products of building or furnishing materials
- Examples
- Polypropylene carpet backing, polyurethane foam, asphalt shingles, PVC plasticisers
Common questions
Why is a substrate interferent a problem specifically in fire debris cases?+
Fire pyrolyses ordinary building and furnishing materials into hydrocarbon fragments that can chromatographically resemble genuine ignitable liquid patterns, such as those from gasoline or a petroleum distillate. Without careful comparison to an unburned control sample from the same scene, an analyst risks reporting an ignitable liquid that is actually just melted carpet backing or foam.
How does an analyst distinguish a genuine ignitable liquid from a substrate interferent under ASTM E1618?+
The standard calls for comparing the target ion chromatogram pattern against reference ignitable liquid classes and, critically, against a matrix control taken from unburned material at the same scene. A pattern that also appears in the uncontaminated control material is attributed to the substrate rather than to an added accelerant.
Related terms
- 4-Vinylcyclohexene (4-VCH)
- A pyrolysis product of styrene-butadiene rubber (SBR) carpet backing, appearing at m/z 108 in the GC-MS. Elevated m/z 108 in a fire...
- Alkene Triplet Pattern
- The GC-MS signature of polypropylene pyrolysis: a repeating triplet of n-alkane, 1-alkene (terminal double bond), and diene peaks at each carbon number...
- Background Subtraction
- The analytical practice of comparing fire debris EIPs against comparison sample EIPs from unburned substrate of the same type. Features present in...
- Comparison (Control) Sample
- A sample of unburned substrate collected from the same room or proximate unburned area as the fire debris sample, of the same...
- Principal Component Analysis (PCA)
- A multivariate statistical method used in fire debris research to reduce chromatographic data matrices to principal components that capture major variance. Used...
- Pyrolysis
- The thermal decomposition of cellulose in paper at approximately 150 to 300 degrees Celsius, disrupting glycosidic bonds and releasing water and carbon...
- SWGFEX Type C Interferent List
- A documented list maintained by the Scientific Working Group for Fire and Explosion Investigation (and continued by OSAC) of substrates known to...
- Type C Interferent (E1618)
- ASTM E1618 designation for a substrate whose pyrolysis products can produce a chromatographic pattern meeting the criteria for an ignitable liquid category....
- Unresolved Complex Mixture (UCM)
- The broad hump of hundreds of co-eluting cycloalkane and isoalkane compounds in the TIC of heavy petroleum products (diesel, heavy fuel oil,...