Same Cannabinoid, Different Product: Why Matrix Effects Matter in Cannabis Testing

Testing for the same cannabinoid across different products isn’t always as straightforward as it sounds. THC in dried flower, for example, presents different testing challenges than THC in an edible or topical. Each product has its own composition, and those differences can affect how a sample is prepared, how the cannabinoid is measured, and how reliable the final result is.

Cannabis testing covers a wide range of product types, from dried and fresh flower to extracts, oils, edibles, beverages and topicals. Even products within the same category can have very different compositions.

Consider topicals. A cream, balm and transdermal patch may all contain the same cannabinoid, but their ingredients and physical properties aren’t the same. A method that works well for one may require further evaluation before it’s used on another.

This is why laboratories need to consider the actual products they test when developing or assessing an analytical method. The goal isn’t simply to detect a cannabinoid. It’s to measure it accurately in the product as submitted.

Health Canada’s latest guidance, Validating analytical methods in cannabis testing, addresses this through the concept of method suitability. A method needs to be shown to work for the product being tested, not just for the compound the lab is trying to measure.

What are Matrix Effects in Cannabis Testing?

In analytical testing, the matrix is everything in a sample apart from the substance being measured. For cannabis products, this can include plant material, fats, sugars, oils, emulsifiers and other ingredients.

Matrix effects occur when other substances in a sample interfere with laboratory testing, causing results to appear higher or lower than the actual value. In cannabis testing, compounds such as oils, waxes, and cannabinoids can interfere with the accurate measurement of pesticides, potency, or other substances.

A dried flower sample is very different from an oil, edible, or topical product. Even when testing for the same cannabinoid, the other ingredients in each product can affect how the test performs. This is why a method that works well for one type of cannabis product may need to be modified before it can be used reliably on another type of cannabis product.

Matrix effects can show up in a few ways:

• Stability: The target compound may react, degrade, or be modified in some way during sample preparation.The rate of these changes can vary depending on the type of product you are testing.
• Extraction efficiency: Some products make it easier or harder to extract a cannabinoid than others. If the preparation method doesn’t account for those differences, the amount measured may not reflect what’s actually in the sample.
• Instrument interference: Other compounds in the sample can affect the

A method that performs well on one type of product isn’t automatically suitable for another. The differences may be small, but they can still affect the reported result.

How laboratories account for Matrix Effects

Method validation helps establish whether a testing procedure produces accurate and reliable results for its intended use. In cannabis testing, that means looking at the entire process, including sample preparation (especially sample preparation), instrument conditions, data processing and reporting.

Health Canada recognizes that laboratories don’t necessarily need to validate every individual product separately. Validation studies typically take 3-4 weeks, so it is not practical to do a validation study on every unique product. Products with sufficiently similar characteristics can be grouped together, with a representative product selected for validation. For example, gummies and hard candies may be grouped as confectionery, with gummies used as the representative matrix. While this is permissible, it is a shortcut, and the ideal situation would be to have a validation study done on your exact product.

The important part is being able to justify that representative grouping decision. Products shouldn’t be grouped together simply because they contain the same cannabinoid or fall under the same broad category. Their similarities need to be relevant to the method and the potential sources of interference.

There is also a distinction between validating a method and bringing an existing method into use. When a laboratory adopts a method that has already been validated elsewhere, it may need to verify that the method performs as expected under its own conditions and for the matrices it intends to test.

When measuring the right cannabinoid isn’t enough

Matrix effects aren’t the only consideration. A method must also be specific enough to distinguish the target compound from other substances that may be present in the sample.

Health Canada’s guidance uses delta-8-THC and delta-9-THC to illustrate this challenge. These cannabinoids have similar chemical structures and can elute close together during chromatographic analysis. If the method doesn’t separate them adequately, one compound may interfere with the measurement of the other.

This is particularly relevant when testing extracts that may contain related cannabinoids or compounds produced during synthesis.

To demonstrate that a method can distinguish between these substances, laboratories evaluate the separation and document supporting evidence. This can include retention times, spectral information and resolution calculations, where appropriate.

The distinction matters because identifying a signal isn’t necessarily the same as confirming which compound produced it. Reliable results depend on the method being able to distinguish the intended analyte from potential interferents.

What happens after validation? Ongoing Quality Control

Validation establishes that a method is suitable for its intended purpose, but laboratories still need to monitor its performance during routine testing. This is where Quality Control (QC) comes in.

Instrument performance can change over time, reagents may vary between batches, and the products being tested aren’t always identical. Ongoing QCl helps identify issues before they affect the reliability of reported results.

Health Canada’s guidance discusses monitoring factors such as calibration, instrument performance, recovery, precision and matrix effects. Additional recovery checks may also be appropriate when a method is used on a matrix that wasn’t adequately represented during the original validation.

The QC checks required will depend on the method, the products involved and the laboratory’s quality procedures. The underlying principle is straightforward: a method needs to continue performing as expected, not just pass validation once.

Bringing It All Together

Before submitting a cannabis product for testing, cannabis producers should discuss the product matrix, the analytes being measured, and whether the method is suitable for that type of product. It’s also worth clarifying sample preparation, how results are calculated, and whether any compounds may be difficult to distinguish during analysis.

At PPB Analytical, we understand that different products can present different testing challenges. If you have questions about your product or testing requirements, contact our team to discuss your needs.

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