Why don't two labs report the same CBD concentration?

You’re comparing two test results for the same flower, and—surprise!—one shows 8.7% CBD, while the other shows 9.4%. Mama, which one is right? Between the sample tested, the method used, and how the cannabinoid levels are calculated, several factors can affect the final number. Let me explain.

Things to remember

• Two test results can differ without a laboratory necessarily being at fault.
• Sampling and the chromatographic method influence the measurement.
• HPLC and gas chromatography do not treat cannabinoids in the same way, particularly because of decarboxylation.

A lab never analyzes your entire CBD flower

The laboratory does not necessarily receive the entire batch.

To analyze a CBD flower, he takes a sample that is supposed to be representative of the product. But every plant is unique.

In fact, flowers can have different concentrations of cannabinoids depending on their size, their position on the plant, their maturity, or the distribution of trichomes.

Imagine a batch containing several hundred grams of flowers. If one laboratory receives a few grams from a given selection and another receives a slightly different sample, the two may obtain different results. This is known as sampling uncertainty.

That is also why a reliable analysis report must make it possible to identify the product or batch in question.

The Problem of Small Sample Sizes

The more heterogeneous the product is, the more representative the sample must be. A large flower that is particularly rich in trichomes may have a different concentration than a mixture that contains more small flowers or plant material.

So, if two laboratories report 8.8% and 9.2%, don't immediately jump to the conclusion that one of them made a mistake; look at how the sample was collected and prepared.

Gas chromatography relies on heat

Gas chromatography, or GC, works differently. The sample is vaporized before being separated and analyzed.

However, cannabinoid acids such as CBDA and THCA are sensitive to heat and can undergo decarboxylation during analysis. CBDA can thus be converted into CBD.

This is where things get interesting, because depending on the method used and how the lab processes the acid forms, the resulting figure may not represent exactly the same thing.

GC may be perfectly suitable for certain analyses, but it should not be naively compared to HPLC as if the two methods always measured the same parameter under the same conditions.

CBD or Total CBD: Be Careful With the Calculation

Here’s another common source of confusion. On a lab report, you might see the following listed separately: CBD: 7.5%; CBDA: 1.8%; and elsewhere: total CBD: approximately 9.1%. But why?

Because CBDA can theoretically be converted into CBD during decarboxylation. The calculation of total CBD therefore takes into account the amount of CBD already present and the fraction of CBDA that is likely to become CBD. The formula used accounts for the difference in molecular weight between the two forms. This is why two test reports may show different numbers even when analyzing very similar material.

Why aren't the results ever exactly the same?

Even when using a similar method, two measurements may show a slight variation. No chemical analysis yields a figure that is completely free of uncertainty.

The performance of the method, sample preparation, instruments, standards used, and analytical conditions all contribute to the measurement uncertainty.

So 8.9% and 9.2% aren't really two different numbers in this case.

What about the legal tolerance limits?

There is no single, uniform tolerance range for CBD that applies to all products and all European countries.

Regulatory tolerances depend on the type of product, the applicable legislation, and how compliance is monitored. For example, the European Commission publishes specific guidelines regarding the tolerances applicable to the nutrition facts declared on food products.

How do you compare two analysis reports?

1. Is it the same batch?

If the two analyses do not pertain to the same batch, the comparison loses much of its value.

2. Is it the same sample?

A laboratory that has received a different strain may, of course, obtain a different concentration.

3. The same method?

HPLC and GC are not based on the same analytical principles.

4. CBD or full-spectrum CBD?

Check whether CBDA is measured separately or included in a total cannabinoid calculation.

5. The same units?

A mass percentage, a concentration in mg/g, or any other unit cannot be directly compared without conversion.

6. Is information about the method available?

A reliable report should make it clear what was measured and under what conditions.