What a GC-MS chromatogram actually is

Gas chromatography (GC) separates the volatile components of an essential oil or aromatic chemical by passing it through a heated column. Each component exits the column at a characteristic time (retention time). Mass spectrometry (MS) then identifies each component by measuring its molecular fragmentation pattern. The chromatogram is a graph: X-axis = retention time, Y-axis = signal intensity (peak height). The taller the peak, the more of that component is in your sample.

What the COA report typically shows

A standard GC-MS report has three blocks:

1. The chromatogram graph itself — visual peaks at different retention times
2. The peak identification table — for each peak, the retention time, the identified compound, and the area% (composition by weight, approximately)
3. The analyst sign-off — quality-control technician name, date, instrument used, column type

What to check on a chromatogram in 4 steps

Step 1: Identify the major peak(s)

Every aromatic ingredient has one or more “marker compounds” that should be the dominant peak. Examples:

• Eucalyptus globulus oil: 1,8-cineole peak should be ~70–85% of total area
• Lavender (true): linalool + linalyl acetate together should be 50–80%
• Thymol crystals: thymol peak should be ≥99% of total area
• Linalool (isolate): linalool peak should be ≥95% of total area
• Patchouli oil: patchoulol peak should be 28–40%

If the major peak is significantly different from spec — red flag.

Step 2: Check the marker-compound ratio

Some species/SKUs are defined by the ratio of two marker compounds, not just one peak:

• Lavender (true) vs lavandin: linalool/linalyl acetate ratio + camphor %
• Eucalyptus chemotypes: 1,8-cineole content distinguishes globulus / radiata / citriodora
• L-Carvone vs D-Carvone: Same chromatogram by retention time — distinguished only by optical rotation, which is reported separately on the COA

Step 3: Scan for unexpected peaks

If the chromatogram shows peaks that aren’t in the SKU’s typical fingerprint — yellow flag. Could be:

• Adulteration with a similar but cheaper material
• Solvent residue from extraction
• Degradation products from poor storage
• Wrong species (e.g., lavandin sold as lavender)

Demand explanation from your supplier before paying the consignment.

Step 4: Check the baseline noise

A clean chromatogram has a flat baseline between peaks. Excessive baseline noise can indicate:

• Instrument calibration issues
• Sample contamination
• Old GC column (analyst should re-run on fresh column)

For high-value pharma or pharmacopoeia-grade SKUs, demand re-run on freshly calibrated equipment if baseline is noisy.

Three GC-MS red flags every procurement manager should know

What to do when chromatogram doesn’t match spec

1. Don’t pay the consignment
2. Send a written discrepancy report to supplier
3. Ask for the retain-sample reference (we keep 36-month retains on every lot)
4. If escalation needed, third-party NABL-accredited lab can re-test the retain sample independently
5. Document the resolution — either supplier replaces the lot or refunds; or the spec is amended in the next PI

How to use chromatograms across multiple lots over time

For repeat-buyer relationships, save every chromatogram in a SKU-specific folder. Over 12–24 months, you’ll see lot-to-lot variation. Within-spec variation is normal (raw material + season + processing). Outside-spec variation is your QC red flag.