How to read a terpene GC-MS report.
The three numbers that actually matter — retention time, peak area, and mass-spectrum match — and how to spot a Certificate of Analysis you can trust.
What GC-MS actually measures
Gas chromatography–mass spectrometry (GC-MS) separates a sample into its individual compounds, then identifies each one by its unique mass spectrum. The output is a chromatogram — a series of peaks — plus a match table showing what each peak is and how much of it is present.
Retention time
Each compound travels through the GC column at a characteristic speed, recorded as its retention time. A peak's position on the time axis is the first identity check: linalool elutes where linalool should. A shifted or extra peak usually signals an impurity or co-eluting compound.
Peak area percentage
The area under a peak is proportional to how much of that compound is present. The "purity" figure on a COA is normally the target compound's peak area as a percentage of total area. A Linalool isolate reporting 99%+ means the linalool peak accounts for over 99% of everything the detector saw.
Be aware that area % is a relative measure — it won't reveal non-volatile or non-GC-eligible material, so it should be read alongside the method notes on the COA.
Mass-spectrum match
The mass spectrometer fragments the compound and compares the pattern against a reference library. A match score (often 90%+) confirms that the peak is genuinely the named compound, not just something with a similar retention time. High retention-time agreement plus a high library match is what makes an identification solid.
What a trustworthy COA includes
- The product or CAS number and batch/lot identifier.
- Test method (e.g. GC-MS) and instrument settings.
- The target compound's retention time, area %, and library match.
- A dated signature and the testing date.
Red flags to watch for
- A COA with no batch number linking it to the material you received.
- "Purity" claimed without a chromatogram or method to back it up.
- Unexplained large peaks that are never identified.
Every Euroterps batch is verified by GC/MS and ships with a COA. Request a COA or MSDS for any isolate or blend to see the data yourself.