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

Significance of the Topic

The accurate measurement of total THC and CBD in Cannabis sativa L. plant material is critical for distinguishing hemp (<0.3% THC) from regulated cannabis. Reliable quantitation ensures legal compliance, consumer safety, and quality control in agricultural, pharmaceutical, and food industries.

Objectives and Study Overview

This study compares two common analytical approaches—gas chromatography with flame ionization detection (GC/FID) and liquid chromatography with ultraviolet detection (LC/UV)—using a unified sample preparation and a suite of standardized cannabinoid reference materials. The goal is to assess method agreement, operational efficiency, and suitability for routine potency testing of hemp flower extracts.

Methodology and Instrumentation

The workflow begins with homogenizing ~500 mg of hemp flower and extracting with methanol. Following a two‐step dilution (1:400 and 1:2,000), aliquots are analyzed by both platforms.

• GC/FID (Agilent 8890): Multimode inlet at 300 °C, DB-35ms column, temperature gradient to 300 °C, hydrogen as carrier gas, FID settings optimized for sensitivity.
• LC/UV (Agilent 1290 Infinity II): Poroshell C18 column, isocratic elution with ammonium formate/formic acid aqueous phase and acidified acetonitrile, detection at 228 nm.
• Standards: Eleven cannabinoids (neutral and acidic) provided as single‐component or mixed solutions at 1 mg/mL.

Main Results and Discussion

Both GC/FID and LC/UV yielded comparable quantitation for total CBD (reported 3.47% vs 3.28% LC and 3.11% GC) and confirmed low levels of total THC (0.17%, not directly detected by either without calculation from acidic precursors). GC/FID analysis converts acidic cannabinoids (CBDA, THCA, CBGA) into their neutral forms during injection, while LC/UV detects both forms directly. Chromatograms demonstrate clear resolution of all 11 cannabinoids under each method.

Benefits and Practical Applications

• Single sample preparation supports multiple analytical platforms without modification.
• Standardized reference materials enable traceable quantitation and method validation.
• Flexibility to choose instrumentation based on laboratory resources and throughput needs.

Future Trends and Applications

Emerging developments include:

• Integration of mass spectrometric detection for lower detection limits and expanded cannabinoid profiling.
• Automation and high‐throughput workflows to meet growing market demand.
• Green extraction techniques and miniaturized systems for field testing.
• Inclusion of novel and minor cannabinoids in regulatory frameworks and product labeling.

Conclusion

This comparative study confirms that both GC/FID and LC/UV methods, when paired with a unified sample preparation and standardized reference materials, deliver accurate and consistent results for total THC and CBD analysis in hemp. Laboratories can select the most suitable platform to ensure compliance and optimize workflow efficiency.

Instrumentation Used

• Agilent 8890 GC with FID detection
• Agilent 1290 Infinity II LC with diode array UV detector
• Agilent MassHunter and OpenLab CDS software

References

Agilent Cannabinoid Reference Standards, part numbers 5190-9430 to 5191-3930, containing eleven cannabinoids at 1 mg/mL in methanol or acetonitrile.