The recently recognized therapeutic potential of cannabinoids has renewed scientific and consumer interest in cannabis, which spurred an increased amount of cannabis-based consumer products on the market. Consequently, there is an increasing need for an accurate and reliable analytical procedure for the quantitative determination of major cannabinoids. The methods of most of the analytical laboratories that perform cannabinoid profiling are based on different types of chromatography involving external standard quantitation. Certified reference materials (CRMs) are characterized by metrologically valid procedures and have a critical role in validating analytical methods and assessing the accuracy and comparability of results among laboratories.
The CRMs are usually provided in methanol solutions with varying concentrations. Light and temperature have been shown to degrade cannabinoids because of which standard solutions are most often kept in the dark at subfreezing temperatures. The preparation of working standard solutions, however, exposes cannabinoid standards to light and increased temperature, which, after repeated use, leads to a certain degree of degradation and consequently adversely affects the accuracy of quantitation. With this in mind, we performed quantification of degradation of several cannabinoid CRM solutions under controlled light and temperature conditions.
Study design and conditions
CRM solutions were exposed to varying experimental conditions:
DARK, FREEZING: 2 ml amber vials at – 20°C
DARK, RT: 2ml amber vials at 20-25°C
LIGHTBOX, AMBER VIALS: 2 ml amber vials at 25-30°C
LIGHTBOX, TRANSPARENT VIALS: 2 ml transparent vials at 25-30°C
The experiments showed that the CRM solutions are stable at -20°C. However, once exposed to room temperature or light, the decomposition of the standards occurs. At room temperature, the neutral components are much more stable than the acidic ones. Interestingly, no differences were observed between complete darkness and the lab environment. However, under intensive light (lightbox), extensive decomposition takes place. Under such conditions, the neutral components are more prone to decomposition compared to the acidic analogues, even in the case of the amber type of glass. In the transparent vials, decomposition up to 100% was observed during a 42-day period.
The conclusion of the study is that attention needs to be paid to the storage conditions of cannabinoid reference standard solutions, as they are light-and heat-degradable. The standard solutions need to be carefully stored in a controlled environment and extra care has to be taken when manipulating is required in order to obtain reliable results.