The legalization of medical and recreational cannabis is causing exponential growth in all facets of this industry. This budding (pun intended) industry has started to mature and is leading to more stringent local and state regulations stretching from the growers, producers, retail outlets, and consumers.
Cannabis testing laboratories include regulatory agencies, traditional agricultural labs, and start-up corporations with a strict focus on cannabis testing. These organizations are involved in determining potency, purity, and safety of cannabis and cannabis-based products. Concerns about the safety of these products revolve around toxic heavy metals that bioaccumulate in plants from the soil and chemical residues like herbicides and pesticides, as well as microbiological contaminants such as mold, mildew, and bacteria. Cannabis is an accumulator plant and, as such, it can pull mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As) from the soil. Based on FDA guidelines some states have set limitations for inhalable cannabis in the range of < 1 µg/g. State agencies where cannabis is legal are in the process of promulgating heavy metals testing requirements for cannabis products.
Certified laboratories are required to report the concentration of each heavy metal and release the sample as pass or fail for heavy metals testing. The determination of metal concentration starts with the time-consuming sample preparation step.
The most common sample preparation techniques for cannabis samples include a microwave and block digestion instrumentation. Closed vessel microwave digestion techniques excel in digesting complex samples using simple acids at temperatures beyond the boiling points of reagents. One limitation of this technique is the small batch sizes. Most microwave instruments are only able to handle less than twenty of these pressurized vessels. This becomes a costly and time-consuming technique for laboratories that need to process large numbers of samples for their clients. Additionally, cleaning the vessels is necessary to eliminate the potential for cross-contamination between sample runs due to metals being present at trace levels.
Over the past twenty years, open vessel digestions increasingly use block digestion instruments that use Teflon™ or PTFE coated graphite blocks. These systems can simultaneously process larger batches of samples (up to 72) compared with the earlier hot plate and beaker methods. Metals content can be determined with accuracy by adjusting the amount and type of acids used during digestion. Furthermore, Block Digestion Systems typically use disposable digestion vessels made from polypropylene. This eliminates the concerns of cross-contamination and the time-consuming activity of cleaning the vessels.
Laboratories that are required to process a high throughput of samples with fast turnaround times are increasingly interested in automated solutions. Studies have shown that sample preparation for metal analysis is responsible for up to 85% of the labor costs associated with the entire metals analysis process. Recent advances in automation specifically target the labor-intensive metals sample preparation process. Automation technologies were introduced in 2001 and have made significant advances over the previous 18 years. Automation is one way to reduce labor expenses and increase the number of samples prepared for analysis. These automated systems can prepare up to 112 samples at one time and will automatically heat, cool, add reagents, perform a final dilution, and transfer an aliquot of the digestate to an autosampler rack for analysis on the mercury analyzer, ICP-OES, ICP-MS, or AA. Most automated digestion systems have their own fume hoods and may be placed directly on the lab bench. This has the added benefit of freeing up space in existing laboratory Fume Hoods. It is essential that the system is constructed with plastic components so that it can survive the corrosive acidic environment. Such automated digestion systems can work day and night and further assist in reducing turnaround times.
LIMS compatibility is an important component for auditing purposes. Instrumentation should be capable of importing sample IDs and exporting sample digestion data for each sample.