To set up analytical equipment to test cannabis samples, scientists need something to go by—a reference standard. Such standards provide known concentrations of chemicals in cannabis, such as delta-9-tetrahydrocannabinol (THC). These can be used for comparison to levels in test samples. For this to work across an industry, vendors of the standards must be selling comparable products. Based on some indications that this might not be the case, we asked some experts about their experience.
“A few years ago, there were some challenges with the inconsistency of these standards,” says Christopher J. Hudalla, founder and chief scientific officer at ProVerde Labs. “However, as the cannabis industry has matured, it has required the vendors to do a better job on these standards.”
Other experts agree that today’s standards can be reliable. “We do not experience inconsistencies in the cannabinoid standards we receive from the manufacturers,” says Eric Wendt, chief science officer at Green Leaf Lab. “It has been our experience that between the two providers we have used, they all prove to be accurate compared to each other.”
The consistency of cannabis reference standards might depend where someone buys them, but the products need to be consistent no matter who makes them. Most testing labs will purchase standards from more than one place. “We use multiple vendors for our reference standards, and compare the samples between different lots and different vendors,” Hudalla says. “For the major chemical vendors, the consistency is now much higher.”
Wendt agrees that the leading vendors provide reliable standards. He says, “We only purchase from the largest two providers, so I cannot speak to the smaller companies.”
Still, a cannabis-testing lab needs to do its own shopping around to find the best vendors. “In the past, there would be larger variance in reported results, depending on whose calibration standards we used to generate our calibration curves,” Hudalla explains. “But now that we have identified the most reliable sources, and do our own internal quality control on incoming batches of samples, we do not have the problems we had in the past.”
So, the analytical labs need to do what is necessary to ensure that they are using reliable standards, and that can mean doing some testing of their own.
Tips in testing
Some of that testing comes from experience, and how you handle the standards matters. “We do experience change over time once the standard vial has been opened,” Wendt says. “Even with storage in the freezer – as specified by manufacturer – the standards will slowly concentrate over time during storage.” He adds, “We have found that the best practice is to open fresh vials when we prepare calibration standards.”
Other aspects of using the standards can also impact the performance. For example, Wendt says, “If you were to use concentrated standards to calibrate the instrumentation, the sample data will trend low as a result.”
In the end, testing labs should pick standards from reliable vendors, test them in-house as needed and run the calibrations and testing as carefully as possible.