How to Read a Cilantro Oil GC/MS Report, Line by Line

A GC/MS report is a list of molecules with percentages next to them. The percentages are shares of what the instrument detected, not amounts of anything, and that one fact changes how the whole page should be read. This article is a reading order for the report on a cilantro leaf oil: what to look at first, what the numbers can confirm, and what no report of this type can prove.

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Start with the misconception: the percentages are shares, not quantities

The figure beside each compound is a peak area divided by the total of all peak areas, then multiplied by 100. In the Portuguese coriander study discussed below, the authors state that percentages came from peak-area integration without correction factors, following ISO 7609, as the mean of two injections (Machado et al., Plants, 2023). Two consequences follow, and both are reasoning from how area normalisation works rather than from a coriander-specific source.

First, the numbers always add to about 100 whatever is in the bottle. If one component shrinks, every other percentage rises. A decanal figure that looks high may mean decanal is abundant, or that something else is missing. Second, anything the column does not elute does not appear. Vegetable carrier oils are made of triglycerides, which are far too heavy to travel through a standard essential-oil method, so an oil that has been cut with a carrier can still print a tidy report. A GC/MS trace cannot tell you the bottle is undiluted. Our leaf oil is sold undiluted with no carrier oil or additives (that is a statement about our process, not something a chromatogram demonstrates), so if undiluted matters to you, that is a claim to weigh alongside the report, not something the report settles.

Step 1: check that the instrument did two different jobs

Two detectors are usually involved. A flame ionisation detector (GC-FID) gives the area percentages. A mass spectrometer (GC-MS) identifies what each peak is. In the Machado study the authors ran both: FID for the percentages, MS for the identity, and they computed retention indices against a C8 to C23 n-alkane ladder, so that each peak's position could be compared with published values. They also matched spectra to a custom library of reference compounds and confirmed identities by 13C-NMR.

The reading rule: a report that gives a compound name should also give a retention time or retention index for it. A name with no position is a library guess. Reasoning from that study, a commercial batch report will usually not go as far as NMR confirmation, so the retention index is the minimum evidence that a name was checked against something.

Step 2: find the leaf signature, and check it against two papers that disagree

This is the check that separates our product from coriander seed oil, and it is why we say leaf, never seed. The Machado study analysed 11 Coriandrum sativum samples from experimental fields in mainland Portugal, hydrodistilled for 3 hours: 3 fruit accessions and 8 vegetative aerial part accessions. Linalool made up 60 to 73% of the three fruit oils. The aerial-part oils were led by 2-trans-decenal at 37 to 63% and n-decanal at 13 to 30%, with 2-trans-dodecenal at 6 to 12%, 2-trans-undecenal at 3 to 6% and 2-trans-tetradecenal at 3 to 4%. The authors propose linalool as a descriptor for fruit oil and the two aldehydes for aerial-part oil.

A second paper looked at fresh leaves of four cultivars (Desi, Peshawari, Irani and a hybrid), steam-distilled, which is the method closer to ours (Kumar et al., Frontiers in Plant Science, 2022). Its oils held (E)-2-decenal at 15.7 to 25.1%, decanal at 14.4 to 18.8%, (E)-2-dodecenal at 12.6 to 13.7%, (E)-2-tetradecenal at 9.1 to 12.9%, (E)-2-decenol at 6.5 to 9.3% and 1-decanol at 4.1 to 7.4%, with aldehydes above 70% of the oil in every cultivar.

CompoundPortugal, aerial parts, hydrodistilled (Machado 2023)Four cultivars, fresh leaf, steam distilled (Kumar 2022)
(E)-2-decenal37 to 63%15.7 to 25.1%
Decanal13 to 30%14.4 to 18.8%
(E)-2-dodecenal6 to 12%12.6 to 13.7%
Linalool as the lead compoundFruit oils only, 60 to 73%Not a lead compound

The two papers agree on the family (decanal, 2-decenal, 2-dodecenal) and disagree on the proportions, by a factor of nearly three for 2-decenal at the top of the ranges. The papers differ in cultivar, growing conditions, plant material (aerial parts versus leaf), and distillation method, so the gap is not evidence that either is wrong. The practical consequence: do not hold a batch to a single "correct" decanal number. Hold it to the pattern. Aldehydes and their alcohol relatives lead, and linalool does not.

The other pattern to look for is what is missing. The fruit-type signature in these papers is linalool far above anything else. A report on a leaf oil that shows linalool as the dominant peak describes a seed-type oil, whatever the label says. Our aldehyde chemistry article explains what these molecules are; this one is only about spotting them on paper.

Step 3: read the footer before the peaks

The footer lines decide whether the table means anything.

What a clean report cannot prove

Origin and freshness. The report says what was in the vial when it was run. It does not say which field, which year, or whether the bottle in your hand came from the same lot.

Natural versus synthetic aldehydes. Decanal and its relatives are ordinary aroma chemicals as well as plant constituents, and aliphatic aldehydes of 10 to 12 carbons are long-standing perfumery materials (Cotton, University of Bristol Molecule of the Month, 2008). Reasoning from chemistry: a molecule is the same molecule whichever way it was made, so a standard GC/MS trace cannot separate a plant-derived decanal from a manufactured one. Telling them apart takes other techniques, and we did not find a published adulteration threshold for coriander leaf oil to give you a number.

Chirality. Chiral columns split mirror-image forms of a molecule. A 2010 study measured the linalool enantiomers in 42 essential oils from 18 genera, including Coriandrum, using multidimensional GC-MS with a chiral column (Özek et al., Records of Natural Products, 2010). That tool is aimed at linalool, which is the seed-oil marker. For a leaf oil whose main peaks are achiral aldehydes, chirality has less to say, which is our inference, not a finding of that study.

A five-minute procedure for any cilantro leaf oil report

  1. Find the lot number and match it to the bottle.
  2. Confirm the top peaks are 2-decenal and decanal type aldehydes, not linalool.
  3. Confirm each named compound has a retention index.
  4. Note who ran the analysis and whether they state accreditation.
  5. Remember what stays invisible: carrier oil, origin, and natural versus synthetic aldehydes.

The shop page for our oil publishes a Certificate of Analysis (PDF), so you can run this procedure on it before ordering. We have not annotated it here, because the point is for you to apply the checklist, not to take our summary. For how the other quality questions fit together, see our buyer's checks article, and for why labels like "therapeutic grade" should not substitute for a report, see what that phrase means.

Cilantro Essential Oil bottle

Cilantro Essential Oil

Cilantro Essential Oil from our own shop, in sizes from 0.5 oz to bulk.

From $13.99

Shop Now →

Sources & Further Reading