Developing Methodology for Moisture Determination in Cannabis

This webinar, presented by Jeff Gast, explores a multi-technique approach to determining moisture (or loss on drying, LOD) in cannabis, highlighting its critical role in regulatory compliance and analytical accuracy. Moisture content is essential for evaluating storage stability, preventing microbial growth, and—most importantly—correcting other analytical results (e.g., THC, CBD, pesticides) to a dry-weight basis. However, standard methods such as USP drying at 105 °C can overestimate moisture because cannabis contains volatile organic compounds (VOCs) like terpenes that evaporate during heating, artificially inflating measured moisture values.

To address this challenge, the webinar introduces a combined workflow using direct moisture/carbon analysis (RC612) and thermogravimetric analysis (TGM-800). The RC612 instrument differentiates true moisture from volatilized organics by simultaneously detecting water and carbon evolution, enabling identification of temperatures where VOC loss becomes significant. Using this approach, the study shows that higher drying temperatures (e.g., 105 °C) produce increased carbon and water signals—evidence of VOC loss—while lower temperatures reduce this interference. The RC612 data is then used to validate a practical, high-throughput thermogravimetric method, ensuring that measured mass loss aligns more closely with true moisture rather than LOD artifacts.

Experimental results across multiple cannabis and hemp samples demonstrate that drying at approximately 80 °C provides a more accurate estimate of true moisture, minimizing VOC loss compared to traditional 105 °C methods. Differences of 2–3% in measured moisture were observed between these temperatures, which can significantly impact downstream calculations—particularly THC content reported on a dry basis. In some cases, this bias could shift a sample from compliant (<0.3% THC) to non-compliant, with serious regulatory and financial consequences. Overall, the webinar underscores the importance of method optimization in cannabis testing and shows how a multi-instrument validation approach can improve accuracy, consistency, and confidence in moisture determination.

Jeff Gast [LECO] discusses an approach for determining proper temperature and analytical gas composition to provide the most accurate moisture value in cannabis, utilizing the RC612 and TGM800.

Originally presented 02 April 2020.