“THC-Free” and the Limits of Testing

by Jake Black PhD

Limits of Quantification and Detection

Every COA indicates a limit of quantification and/or a limit of detection, but what are they and why do they matter? These limits are important because they provide an understanding of what an analytical lab is actually able to measure. This is especially important when purchasing products marketed as “THC-free”.

Imagine you are taking a photo of an apple tree and a friend asks, “How many apples are on that tree?” How do you answer? And how could you provide a more accurate answer to your cider-loving friend? If you took the photo on your iPhone from a distance so you could capture the sunset behind the tree, an accurate answer is going to be nearly impossible. Perhaps you could zoom in but at some point distinguishing apples from leaves in a pixelated mess will only get you so far. Your ability to distinguish leaves from apples is the limit of detection. Maybe with this photo you could make a guess at say twenty apples.

Now imagine instead of your iPhone, you set up a tripod and used a fancy zoom lens to take an immaculately detailed photo of just the top of the tree. You would be able to count exactly how many apples are visible to you from the photo, let’s say 42. How many apples you can individually count from this vantage point is the limit of quantification. The second photograph gives you a far more accurate view of how many apples there really are, but short of cutting the tree down and harvesting every apple – they are both just guesses limited by your view.

This is how analytical chemistry and the quantification of compounds like cannabinoids work. The answer very much depends on the equipment you use (an iPhone vs a telephoto lens) and how accurate you need the answer to be (a ballpark using a photo vs dead on accuracy by physically harvesting and counting every actual apple). When thinking about “THC-free” products in the hemp industry, it is useful to think along similar lines. How accurate of a result do you need? How detailed (or zoomed in) do you need to go?

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