Real-Time, Four-Year Storage of Cannabis Resin

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In 2019, there are many problems with the analytical chemistry of cannabis products. The lack of science-based study and reports of the many variables is very frustrating to lab staff as well as people working in the supply chain. It is refreshing to see some reports that make it through the review process.

For example, Karin Grafström and colleagues at the Swedish National Forensic Centre (Linköping, Sweden) reported on about 43,000 cases involving suspected illicit drug,¹ 10,000 of which appeared to contain cannabis resin. The authors focused on three major and 16 minor constituents and metabolites using gas chromatography with flame ionization detection (GC-FID). The primary stated purpose was to classify composition to aid in tracing the supply chain back to the origin. Important variables investigated included storage temperature and exposure to light and air. The study traced the aging for 48 months.

Cannabis resin is derived by extraction of the resin from trichomes of cannabis plant material. The resin has THC, CBD, and CBN content. Since the resin does not burn well, even in a pipe, it is often mixed with a more combustible material such as tobacco of cannabis plant material to form hashish. Nonsmokable end products containing cannabis resin such as gummy bears and cookies are also common.

The paper from Grafström et al. reports that the method of storage has a very strong effect on composition. Samples stored in plastic bags at –20 °C in a dark freezer were unchanged at the 99% confidence level after four years. In contrast, storing the samples in air at room temperature decreased the THC content by 64–74%. Storage under ambient light and temperature, but sealed from air, showed a loss in THC of 25–42%. However, the authors point out that the analytical samples were taken from the interior of the slabs, where light might be less intense due to self-absorption of the sample.

I want to thank the authors for describing the experimental procedure in detail. Assay, and particularly sampling of a heterogenous complex material, is difficult. To maintain the protocol for four years is commendable.

Reference

1. Grafström, K.; Andersson, K. et al. Effects of long-term storage on secondary metabolite profiles of cannabis resin. Forens. Sci. Int. Aug 2019, 301, 331–40.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]