Expert Insight: Pesticide residue analysis in cannabis: Method fundamentals and confirmation strategies

In this on-demand webinar, cannabis and hemp consultant Julie Kowalski explains why confirmation testing is a must when screening for residual pesticides in consumer products

15 Jan 2021



Julie Kowalski, Cannabis & Hemp Consultant, JA Kowalski Science Support, LLC

Pesticide residue testing is challenging but even more so when testing pesticides in cannabis. It can be hard to know where to start with method fundamentals but luckily, the chemical contaminants community has developed excellent guidelines that can be used. It is important to understand the fundamental criteria for basic method development.

Establishing a truly robust method can help mitigate long-term problems and add confidence to results. It can be stressful to tell a client that their sample tested positive for pesticides especially if it failed regulatory requirements. In the cannabis market, this situation will often prompt questions about the validity of the results. In addition to suitable method criteria, confirmation strategies can be employed to verify results and reassure clients.

In this SelectScience webinar, now available on demand, Julie Kowalski, a cannabis and hemp consultant at JA Kowalski Science Support, LLC, discusses confirmation method strategies, including examples that demonstrate the importance of using confirmation testing.

Read on for highlights from the Q&A discussion at the end of the live webinar or register to watch the full webinar on demand >>

Q: What technical problems are most common, specifically regarding pesticide testing in the cannabis market?

JK: Cannabis is extremely difficult to analyze for a couple of reasons; it is complex, meaning it has a lot of coextracted compounds and, at the same time, it has a high percentage of specific compounds, cannabinoids. The combination of these factors causes the sample to be dirty with methods commonly used. This causes major issues with data quality especially sensitivity and instrument cleanliness. The pesticide residue community has moved towards achieving “good enough” sample preparation over the past 15 years, something that has been facilitated with the introduction of QuEChERS. It works well for many food commodities but not for cannabis. Finding robust sample preparation is one of the biggest technical problems. I think there is still room for improvement there.

The other issue is best practices. Performing trace-level analytical chemistry has its own rules, guidelines and best practices. These rules are not something that is going to be taught in your basic analytical chemistry class. I have been lucky to know people with this kind of experience who were willing to teach me. I see misunderstanding and misapplied analytical chemistry when people start working on pesticide testing for the first time. Working at high levels with a forgiving technique like LC-UV for cannabinoids analysis is simply different than trace level pesticide work on tandem mass spectrometers. Trace level work is not as straightforward and requires you to understand what is really achievable. It also tends to be more work and that is just something that people have to accept.  

Q: Do you have any general advice on what to look for when implementing methods to fit this kind of testing?

JK: Some of the best resources are from vendors. Either instrument vendors or consumable vendors. They develop methods and perform a certain amount of verification on those methods. That is a good place to start. It is often hard to get some of the fine details right and some methods are better starting points than others. If you are in the market for purchasing instruments, a lot of instruments will come with helpful databases. Some have transition databases, sometimes even retention time information, which can provide shortcuts. Therefore, if you're willing to run their canned method with their retention time, they will give you transitions that should be optimized for their platform. This is because they are not transferable all the time. Government agencies will also have guidance documents that are extremely useful. I believe I mentioned two of my favorites in the presentation, FDA and SANTE. 

Q: Regarding control strategies, you mentioned getting many points on the peak. Do you have any advice on how to find a common medium with runtime and data quality?

JK: To find a happy medium, it comes down to a personal preference on how comfortable somebody is with the data quality. If you are really stretching these scans, you are likely to get more of that geometric peak shape. At some time that degrades to a point where the retention time is affected but also your quantitation is affected. I would not recommend dipping down to where you see inconsistencies in quantitation because of your scan speed. A general rule of thumb would be to not go below roughly seven points across the peak. I prefer to go to about nine or ten at a minimum. However, at times this can be difficult to obtain. 

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