# Gas chromatography

> Gas chromatography (GC) separates volatile compounds in a heated gas stream; it is used for terpenes and residual solvents and decarboxylates acid cannabinoids in its hot inlet.

- Canonical: https://genetixbay.com/knowledge/glossary/gas-chromatography.html
- Also written: GC, GC-FID, GC-MS, gas chromatograph, GC testing
- Glossary category: Lab testing · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

In gas chromatography the sample is vaporised in a heated inlet and carried by an inert gas through a long, thin column. Compounds separate by volatility and their interaction with the column coating, then reach a detector: a flame ionisation detector (GC-FID) for quantification, or a mass spectrometer (GC-MS) for identification.

## In practice

GC is the standard for [terpene profiles](https://genetixbay.com/knowledge/glossary/terpene-profile.md) and residual solvent testing, often with headspace [sampling](https://genetixbay.com/knowledge/glossary/homogenisation.md) (analysing the vapour above a sealed sample). Specialised setups, such as two-dimensional GC with sulfur detection, found the prenylated [thiols](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) behind skunk aroma. For [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), GC has a built-in problem: the hot inlet [decarboxylates](https://genetixbay.com/knowledge/glossary/decarboxylation.md) [THCA](https://genetixbay.com/knowledge/glossary/thca.md) to [THC](https://genetixbay.com/knowledge/glossary/thc.md), and the conversion is not always complete or consistent. Without a derivatisation step, a GC potency result reports mostly neutral THC and cannot separate the original THCA and THC. That's why potency is normally done by [HPLC](https://genetixbay.com/knowledge/glossary/hplc.md).

## Don't confuse with

- **HPLC**: liquid-phase, room temperature, measures acids directly.
- **GC-MS for pesticides**: the same technique family, but a different method and panel.

## Related terms

[HPLC](https://genetixbay.com/knowledge/glossary/hplc.md), [Terpene test](https://genetixbay.com/knowledge/glossary/terpene-test.md), [Residual solvents](https://genetixbay.com/knowledge/glossary/residual-solvents.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md)

## Sources

1. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271.
2. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196