Acidic and Neutral Cannabinoid Analysis in Cannabis and Hemp by GC

Introduction

Cannabinoids in cannabis and hemp exist in two forms: acidic and neutral. Acidic cannabinoids such as THCA and CBDA convert into their neutral forms, THC and CBD, through heat or ageing. These forms have different chemical behaviours and biological effects.

Measuring both provides a fuller picture of a product’s potency and consistency. It helps growers and processors understand how decarboxylation affects their material and verify total cannabinoid content with confidence.

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The Challenge

Measuring both acidic and neutral cannabinoids isn’t straightforward

Cannabinoids naturally exist in two forms that change with heat and time. Acidic cannabinoids such as THCA and CBDA slowly decarboxylate into their neutral forms, THC and CBD. This transformation happens during drying, extraction, and even storage, which makes it difficult to know exactly how much of each form is present in a sample.

The ratio between acidic and neutral cannabinoids affects potency, stability, and how a product behaves when heated or consumed. Understanding both helps producers manage processes like decarboxylation and standardise their products for consistency.

However, because the heat inside a gas chromatograph causes complete decarboxylation, only the neutral forms are normally detected. That means the acidic portion is lost during analysis, making it hard to measure total cannabinoid content accurately without extra preparation.

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The Solution

Derivatisation makes it possible to separate and measure both forms by GC

Gas chromatography (GC) offers a fast, reliable way to measure cannabinoid content with excellent separation and repeatability. When combined with a simple derivatisation step, it can quantify both acidic and neutral cannabinoids in a single analysis.

The Ellutia 200 Series GC, fitted with a Flame Ionisation Detector (FID) and paired with a liquid autosampler such as the EL3000A, provides accurate and consistent results across a wide range of cannabis and hemp products.

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Derivatisation chemically stabilises the acidic cannabinoids so they no longer convert to their neutral forms during injection. This allows clear detection of both forms while maintaining GC’s speed, low running cost, and ease of operation.

With this setup, producers can track decarboxylation, verify potency, and monitor product consistency from raw material through to final extract.

If you’d like an overview of how GC fits into cannabis testing workflows, take a look at the Cannabis Testing Buyers Guide.

Method Overview

How the derivatised GC method works

An aliquot of individual standards and a 12-cannabinoid stock solution were evaporated to dryness under nitrogen. Derivatisation was performed using BSTFA + 1% TMCS and heating at 90 °C for 30 minutes. Samples were cooled, dried again, and reconstituted in methanol before injection.

Typical GC Conditions

Injector temperature: 270 °C
Detector: FID
Detector temperature: 280 °C
Carrier gas: Hydrogen
Constant pressure: 9.3 psi
Split flow: 70 ml/min
Column: EL-5 30 m × 0.25 mm × 0.25 µm

LC vs GC for Acidic and Neutral Cannabinoid Testing

Learn how gas chromatography can measure both acidic and neutral cannabinoids using a simple derivatisation step. This video explains the key differences between LC and GC approaches, how GC achieves total cannabinoid measurement, and what makes it a practical option for in-house testing.

Results and Reliability

What the analysis shows

The method achieves strong separation and repeatable quantification of both acidic and neutral cannabinoids. Example results show distinct peaks for derivatised THCA, THC, CBDA, and CBD standards, confirming effective stabilisation and reliable signal response across repeated runs.

Derivatised cannabinoid standard mix
Individual THCA and THC standards
Cannabis extract sample
Hemp oil sample

The chromatograms show clear, well-resolved peaks and stable baselines, with no carry-over or background interference. The results confirm that derivatised GC-FID analysis can accurately measure both forms in a single run while maintaining high repeatability.

Testing both forms provides a true total cannabinoid value and helps producers understand how decarboxylation affects potency and product quality.

Curious how this could work in your own lab?

Learn More

Get the full method and results

If you’d like to see the full details behind this testing method, you can download the complete application note. It includes chromatograms, calibration data, and the exact conditions used for the analysis. It’s a handy reference if you want to check your own setup or compare results.

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