Qualitative and quantitative analysis of the cannabinoid content of combusted cannabis plant tissue

Abstract

Marihuana continues to be a controversial topic in today’s society. The plant material is used recreationally as a stupefacient and has a purported medicinal use. In fact, anecdotal information about its medicinal properties has been such that Health Canada has recently started an initiative to provide a well characterized supply of plant tissue to researchers interested in examining its potential medicinal properties. Simultaneously this same material is being provided for those subjects who are licensed to use marihuana as a medicine. In order to further study marihuana and its component cannabinoids it is essential to be able to discern both the cannabinoid content in the product being supplied and more importantly the cannabinoid profile in the delivery system. At present the most common route of administration is via inhalation of the combusted plant material. Consequently methods capable of measuring the cannabinoid content in combusted plant material would be very useful in order to make meaningful study of the pharmacokinetics of the cannabinoids delivered by this route. Investigations were carried out to develop a method and study the volatile constituents of combusted marihuana plant material in a semi-enclosed environment. Thus the hypothesis of this research is that qualitative and quantitative information can be obtained from the combustion products of cannabis plant tissue. The method relies upon the solid phase extraction of smoke arising from the combustion of plant material in a variety of combustion chambers. The combustion chambers were designed to reflect the current marihuana “paraphernalia” in use as well as a high efficiency in vitro system. Both the qualitative and quantitative levels of a limited number of cannabinoids were evaluated before and after combustion. A quantitative Liquid Chromatography Ultra Violet (LC-UV) detector method was validated for the analysis of a selected group of cannabinoids ( Δ9-tetrahydrocannabinol (THC), cannabinol (CBN), cannabidiol (CBD) and tetrahydrocannabinolic acid (THCA) . When this method was applied to plant material available through the medical marijuana initiative the following observations were made on the combustion products: MATERIAL ANALYZED CBD μg/mL CBN (μg/mL) THC (μg/mL) THCA (μg/mL) PLANT BLQ BLQ BLQ 890 COMBUSTED 20 14 420 28 • 5 mg plant tissue extracted using a validated HPLC-UV method • 5 mg plant tissue combusted in a closed combustion chamber. • BLQ: below level of quantification (<12.5 μg/mL) These results sparked further research into the quantitative transformation of cannabinoids during the combustion process. In this regard, it was shown that THC, CBD and CBN all could be recovered at approximately a 90% ratio upon combustion. However, THCA was thermally converted such that very little remains after combustion and furthermore, its degradation product, THC can only account for 50% of the THCA. The latter observation is important since there has been a prevailing thought that THCA is quantitatively transformed during combustion to THC while in fact this transformation is approximately 50%. This finding must be considered when pharmacokinetic studies are carried out using inhalation of combusted plant material as the delivery system. A further finding of this research is that not all popular combustion devices yield identical quantitative cannabinoid profiles. In this regard, the simpler “pipe” systems result in the highest yields of heat transformed cannabinoids while the vaporizer systems have the lowest cannabinoid yields