Chocolate and cannabis make a hash of things


Matrix effect makes it hard to assess product potency. 


Even chemists have difficulty telling exactly how much cannabis is in the recipe.

Vladislav Nosick / 500px, via Getty Images

Where cannabis products are legal it can be difficult to ensure they are legal, US chemists have found.

In a paper prepared for this week’s American Chemical Society meeting in San Diego, they describe how components in chocolate – a common ingredient in many cannabis-infused edibles – might be interfering with cannabis potency testing, leading to inaccurate results.

And that can be a major problem if they do need to be accurate.

"If an edible cannabis product tests 10% below the amount on the label, California law states that is must be relabelled, with considerable time and expense,” says principal investigator David Dawson.

“But it's even worse, if a product tests 10% or more above the labelled amount – then the entire batch must be destroyed."

Manufacturers add cannabis to a wide variety of foods, Dawson says, and the composition of these products, known as the matrix, can affect potency testing results.

He and colleagues at CW Analytical Laboratories, a cannabis testing laboratory in Oakland, California, decided to focus on cannabis-infused chocolates because they are a very common product. "We also noticed, kind of anecdotally, some weird potency variations depending on how we prepared chocolate samples for testing," he adds.

They studied the impact of altering a few variables, including the amounts and type of chocolate, on the concentration of Δ9-THC, the major psychoactive constituent of cannabis, measured by high-performance liquid chromatography.

Their results were surprising. "When we had less cannabis-infused chocolate in the sample vial, say one gram, we got higher THC potencies and more precise values than when we had two grams of the same infused chocolate in the vial," Dawson says.

"This goes against what I would consider basic statistical representation of samples, where one would assume that the more sample you have, the more representative it is of the whole."

These results suggest that some other component of the chocolate – a matrix effect – was suppressing the signal for Δ9-THC.

"Simply changing how much sample is in the vial could determine whether a sample passes or fails, which could have a huge impact on the producer of the chocolate bars, as well as the customer who might be under- or overdosing because of this weird quirk of matrix effects," Dawson says.

Now he’s trying to figure out exactly which ingredient of chocolate is responsible for the matrix effects. He has tried spiking a standard solution of Δ9-THC with varying amounts of chocolate bar, cocoa powder, baker's chocolate and white chocolate, all of which have different components, and observing how the HPLC signal changes.

"Our best lead right now is that it has something to do with the fats, which makes sense considering that Δ9-THC is fat-soluble," Dawson says.

Eleven US states have legalised the recreational use of cannabis. Uruguay and Canada are the only countries to have legalised it nationwide.

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  1. https://plan.core-apps.com/acs_sd2019/abstract/3f1890e3-308d-4e54-bfd7-aee1257ef814
  2. https://en.wikipedia.org/wiki/Legality_of_cannabis
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