Digestion of Various Cannabis Samples for Trace Metal Analysis with ICP-MS

Although prohibited in the early 20^th century, cannabis is now undergoing resurgence in medical and recreational use. In recent years more and more countries legalized the use of medical marijuana and Uruguay, Canada, Georgia as well as some US states also legalized recreational use of cannabis. Compared to the well-established system of cultivation, processing and sales of cannabis products, the governmental regulations of quality control are far behind. There is a lack of standardized methods and each state is currently responsible for regulating the quality controls, leading to multiple different legal situations. However, to ensure consumer safety and product quality cannabis-based products and the plant material itself must be tested for the potency of active ingredients, the presence of pesticides and toxic heavy metals like arsenic, cadmium, mercury and lead. These metals are of special interest as they are hazardous to humans even at low concentrations.

During growth plants absorb trace elements from soil, fertilizers and pesticides which can accumulate in the plant material. This effect based on natural metabolism may lead to high concentrations of toxic heavy metals in cannabis plants which are transferred to the final products opening the possibility of harming the consumer. It is of governmental and producer’s interest to test for heavy metals content in order to ensure consumer safety and high product quality.

The huge variety of matrices of cannabis products result in unique challenges for sample preparation prior element analysis. Samples like oil, extract or flower produce significant amounts of reaction gases during digestion which limits the sample amount of hermetically closed vessels. The pressurized digestion cavity (PDC) of the Multiwave 7101/7301/7501 series offers the opportunity to digest different reactive organic samples within one single run. The PDC can operate up to 199 bar allowing the digestion of huge amounts of organic samples and the combination of different matrices in one run. This enables high sample throughput and fast method development.

In order to demonstrate the suitability of the Multiwave 7101/7301/7501 series and its PDC for sample preparation of various cannabis products within one run prior to element analysis the recovery rates of spiked samples were determined for As, Cd, Hg, Pb.