In the cannabis industry, proficiency testing (PT) is a necessary, yet oftentimes difficult activity because of U.S. federal laws surrounding the plant. It allows growers and producers to test their products for a variety of things, including potency and THC content, pesticide residues, residual solvents, moisture content, heavy metals, mycotoxins, terpenes, and microbes. Then, the results are compared against pre-established criteria by means of large-scale interlaboratory comparisons (ILC). Also known as Round-Robin Testing, ILC is the evaluation of measurements or tests on the same or comparable items by multiple laboratories in accordance with predetermined conditions.
PT samples are distributed by a third-party organization to cannabis testing laboratories all over the world. There are a variety of schemes depending on the matrix type, the analytes being tested, and the technology used. Participating labs test products against the PT sample, submit their results to the third-party distributor, and the PT provider aggregates the results and calculates z-scores—which measure the distance between a data point and the mean using standard deviations. The PT provider uses these z-scores to determine if you have passed the proficiency test.
There are many reasons to conduct PT and ILC, especially for labs seeking or maintaining ISO/IEC 17025:2017 accreditation. PT meets the requirements for clause 6.2.5 which includes monitoring competence for personnel and allows laboratories to identify problems areas of improvement, such as in the equipment, training, or methods. PT also builds customer confidence, validates uncertainty claims, reduces the chances of lab shopping, and can be used to identify differences between labs as an educational opportunity.
The Problem with PT
To maintain accreditation, cannabis labs must demonstrate successful participation in PT programs to cover the tests on their scope and within the current accreditation cycle. However, because cannabis is federally illegal in the United States, quality compliance samples must stay within its state of origin. Samples with more than .3% THC potency cannot cross state lines, requiring labs to use hemp and hemp oil instead. Using hemp as a compliance sample instead of a finished product creates a less realistic testing comparison and requires methods not typically used.
Despite the difficulty, labs can still conduct PT using hemp and hemp oil obtained from verified Proficiency Testing Providers (PTPs). For example, NIST offers homogenized hemp oil and ground hemp matrices in their PT program and Phenova offers different hemp samples for different states depending on their testing regulations. When using these compliance samples, labs typically use the prescribed test methods instead of their internal Standard of Procedures (SOPs).
Another way for cannabis labs to perform PT testing is to obtain compliance samples from PTPs within the same state. Depending on the state in which you operate, there are programs that coordinate the sharing of compliance samples among multiple labs. Known as round-robin testing, these programs can be found in many states including Colorado, Maryland, and Oregon. Round-robin testing allows laboratories to use realistic compliance samples for their proficiency testing instead of hemp or hemp oil, which requires different test methods.
Currently, there is no agreement among states on which pesticides to target nor their regulatory action levels. To add to this complication, pesticide testing is trace-level analysis which means that the limits can be close to the limit of quantitation and limit of detection causing testing challenges and lower confidence in results. These challenges include matrix interferences and matrix effects.
Matrix interferences are coextracted compounds that produce or interfere directly with mass spectral information. Cannabis is complex and variable which increases the opportunity for interferences. These interferences typically corrupt the ability to both identify and quantify pesticides in cannabis. Matrix effects are changes to signal of an analyte due to the presence of matrix (coextracted compounds) when tested.
Generally, matrix effects are evaluated by comparing analyte signal in solvent versus in-matrix. Two forms of matrix effects, ion suppression and ion enhancement, are observed and are analyte/matrix pair specific and related to the testing technique. Ion enhancement occurs if the analyte signal detected in the cannabis matrix is greater than in solvent only and ion suppression means that the signal detected in the cannabis sample is less than signal in solvent only. Generally, if the signal difference between solvent and in the cannabis matrix is more than 20%, then the matrix effects are considered significant and must be mitigated.
Cannabis complexity and high concentrations of cannabinoids correlates with greater potential for matrix interferences and more severe matrix effects. Trace level testing of pesticides under these complications could lead to under or over-reporting or over-reporting of pesticides or potentially false-fail or false-pass scenarios based upon the measurement uncertainty and decision rule. This further indicates why proficiency testing for pesticide residues should take into account both the cannabinoid concentration and regulatory limits.
Mitigating Lab Shopping
In the cannabis industry, the practice of lab shopping—producers and growers sending samples to multiple labs to find the best results—is detrimental to the integrity of lab results. Lab shopping puts laboratories in a difficult position, forcing them to choose between giving accurate results and earning the business of their customers. However, PT is helping to mitigate this practice as labs are less likely to manipulate results, as it is easier to detect manipulation in blind ILC PT of finished products.
To mitigate lab shopping even more, many states have recently added a two-lab rule to its cannabis regulation, allowing regulators to send samples to a second lab to verify results. For example, in Pennsylvania, growers and producers are required to test their products twice by two different labs. In Oregon, regulators reserve the right to send product samples to a lab of their choosing to verify lab results. This rule is intended to reduce the practice of lab shopping and reduce the inflation of potency percentages, while keeping labs accountable.
Developments in Proficiency Testing
Cannabis laws and regulations are constantly evolving, and frequent changes can prove to be problematic for PTPs and laboratories trying to keep up. As labs are required to test for more variables and the presence of more compounds, PTPs must develop new samples that include the elements labs are required to test for, including synthetic cannabinoids. It will be up to PTPs to quickly provide the samples necessary for laboratories to properly abide by changing regulations.
For labs working to achieve or maintain their accreditation, successful proficiency testing can prove competency and build confidence in your product. Have more questions about cannabis proficiency testing or achieving ISO/IEC 17025:2017 accreditation? Ask us at A2LA! Visit our website or reach out to us at info@A2LA.org.