Alkene Triplet Pattern
Definition
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 from C5 to C15, visible in the TIC and confirmed by elevated m/z 55 (alkene fragment) in the extracted ion profile.
- Source polymer
- Polypropylene pyrolysis
- Analysis method
- GC-MS
- Pattern components
- n-alkane, terminal alkene, diene per carbon number
- Carbon range
- C5 to C15
- Confirming ion
- m/z 55
Common questions
Why does a triplet of three related peaks appear at each carbon number instead of one?+
Thermal breakdown of the polypropylene chain produces fragments that terminate in different ways at random scission points, generating a saturated alkane, an unsaturated terminal alkene, and a diene at nearly the same carbon number for each pyrolysis event.
Why check the m/z 55 extracted ion rather than relying on the total ion chromatogram alone?+
The full TIC can contain overlapping peaks from co-eluting compounds or background material, so extracting the m/z 55 alkene fragment isolates the specific triplet pattern from interferents and confirms the polypropylene identification more reliably.
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