A Comparison of Quantitation of Cannabinoids in Hemp Using GC/FID and LC/UV

Significance of the Topic

Cannabis sativa L. classification as hemp or cannabis depends critically on the total THC content. Accurate measurement of cannabinoids ensures compliance with regulatory limits (0.3% THC in the U.S.) and underpins quality control in pharmaceutical, food, and industrial applications.

Study Objectives and Overview

This work compares two analytical approaches—gas chromatography with flame ionization detection (GC/FID) and liquid chromatography with ultraviolet detection (LC/UV)—for quantifying total THC and CBD in hemp flower extracts. The study evaluates the consistency of results obtained using a unified sample preparation protocol and a suite of Agilent cannabinoid reference standards.

Methodology and Instrumentation

The common sample preparation procedure included:

• Weighing ~500 mg of homogenized hemp flower and adding 20 mL methanol.
• Mechanical shaking (10 min), centrifugation (5 min at 5 000 rpm), and filtration.
• Serial dilutions: 1 mL extract to 20 mL methanol (1:400), then 1 mL of the first dilution to 20 mL methanol (1:2 000).

Instrumentation details:

• GC/FID: Agilent 8890, multimode inlet (300 °C), DB-35ms Ultra Inert column (30 m×0.25 mm×0.25 µm), He carrier (1.4 mL/min), temperature program (90 °C to 300 °C), FID flows, injection 1 µL.
• LC/UV: Agilent 1290 Infinity II, Poroshell 120 SB-C18 column (3.0×75 mm, 2.7 µm), mobile phases A (5 mM ammonium formate/0.1% formic acid in water) and B (0.1% formic acid in acetonitrile), 0.425 mL/min, 35 °C, isocratic (72% B), UV detection at 228 nm, injection 5 µL.
• All analyses used Agilent MassHunter and OpenLab CDS software.
• Agilent cannabinoid reference standards (11 components) provided calibration and quantitation.

Main Results and Discussion

Both GC/FID and LC/UV methods produced comparable quantitation of total CBD and THC in hemp extracts. GC analysis decarboxylates acidic cannabinoids (CBDA, THCA, CBGA) to their neutral forms, while LC/UV detects both acid and neutral forms. Calculations applied:

• Total CBD = [CBD] + 0.88×[CBDA]
• Total THC = [Δ9-THC] + 0.88×[THCA]

Result comparison for hemp composition:

• CBD + CBDA: reported 3.47% (3.28% by LC/UV, 3.11% by GC/FID)
• Δ9-THC + THCA: reported 0.17% (below detection by both methods)

Chromatographic profiles confirmed resolution of 11 cannabinoids in the respective analysis modes.

Benefits and Practical Applications

• Single extraction and dilution workflow supports multiple detection platforms, streamlining laboratory operations.
• Comparable accuracy between GC/FID and LC/UV enables flexible instrumentation choices.
• Agilent’s reference standards and software facilitate robust calibration and data analysis.

Future Trends and Potential Applications

• Integration of high-resolution mass spectrometry could expand specificity for minor cannabinoids and contaminants.
• Automation of sample preparation may improve throughput for large-scale potency testing.
• Development of portable GC/FID or LC/UV systems could support on-site compliance testing in agricultural and industrial settings.
• Enhanced software analytics and AI-driven data interpretation promise further improvements in accuracy and workflow efficiency.

Conclusion

A unified sample preparation protocol combined with Agilent cannabinoid standards enables reliable quantitation of total THC and CBD using either GC/FID or LC/UV. Both techniques yield consistent results, offering laboratories the flexibility to select instrumentation based on existing resources and specific testing requirements.

References

No external literature references were provided in the original document.