Quality control of dried cannabis

Importance of the Topic

Cannabis is widely used both recreationally and medically, driven by its main active compounds—THC, CBD, and CBG. Accurate profiling of these cannabinoids is essential for legal compliance, quality assurance, and therapeutic consistency in pharmaceutical, nutraceutical, and industrial applications.

Objectives and Overview of the Study

This study evaluates near-infrared spectroscopy (NIRS) as a rapid, reagent-free alternative to high-performance liquid chromatography (HPLC) for quantifying THC, CBD, and CBG in dried cannabis. A total of 702 samples with diverse cannabinoid concentrations were analyzed to develop and validate predictive calibration models.

Methodology and Instrumentation

The experimental workflow included manual grinding of 400 mg sample aliquots, placement in a NIRS mini sample cup, and transflection measurement using a gold diffuse reflector. Key instrumentation and software comprised:

• Metrohm DS2500 Solid Analyzer (400–2500 nm spectral range)
• DS2500 Holder and NIRS mini sample cups with disposable backs
• 4 mm gold diffuse reflector for transflection measurements
• Vision Air 2.0 Complete software for data acquisition and model development

Main Results and Discussion

Vis-NIR spectra of all samples were used to build prediction models. Model performance was assessed by correlation to reference HPLC values and expressed via key figures of merit:

• THC prediction: R² = 0.979, SEC = 0.71 %, SECV = 0.73 %
• CBD prediction: R² = 0.978, SEC = 0.74 %, SECV = 0.75 %
• CBG prediction: R² = 0.849, SEC = 0.16 %, SECV = 0.17 %

High correlation and low error values demonstrate that NIRS can reliably quantify major cannabinoids in under one minute per sample, offering comparable precision to HPLC without chemical reagents.

Benefits and Practical Applications of the Method

NIRS provides several advantages for routine cannabis quality control:

• Rapid analysis: results in less than 1 minute, saving up to 30 minutes compared to conventional HPLC
• Chemical-free and non-destructive measurement
• Minimal sample preparation with simple grinding and cup loading
• Robust, maintenance-friendly instrumentation suitable for laboratory and production environments

Future Trends and Opportunities

Advancements in calibration transfer and machine learning could further improve accuracy and extend NIRS applications to minor cannabinoids and other plant matrices. Integration into inline or at-line production monitoring systems may enable real-time quality assurance in commercial cannabis processing facilities.

Conclusion

This study demonstrates that NIRS on a Metrohm DS2500 Solid Analyzer is a fast, reliable, and cost-effective method for quantifying THC, CBD, and CBG in dried cannabis. The approach streamlines quality control workflows and reduces reliance on solvents and reagents, aligning with industry demands for sustainable analytical techniques.