A sample is homogenised, the compounds are dissolved out with a solvent, and the mixture is separated by chromatography — usually HPLC, which does not heat the sample and so can report acid and non-acid forms separately. Results are then compared against calibrated reference standards.
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Knowing roughly how the figure was produced explains most of the odd things about certificates: why two laboratories disagree, why a total is calculated rather than added, and why sampling gets its own line on the report.
1. Sampling. A portion is taken from the batch. How it was taken matters enormously, because a single grab from one corner does not represent a run. 2. Homogenisation. The sample is ground or mixed so it is uniform. Uneven material is the largest source of disagreement between laboratories. 3. Preparation. The compounds of interest are dissolved out with a solvent and diluted to a workable concentration. 4. Separation. The mixture is pushed through a chromatography column, which separates compounds by how strongly they interact with it. 5. Detection and quantification. A detector measures each compound as it emerges, and the result is compared against reference standards of known concentration.
| Method | How it works | Consequence |
|---|---|---|
| HPLC — high performance liquid chromatography | Liquid solvent, no heat | Reports acid and non-acid forms separately |
| GC — gas chromatography | The sample is vaporised | Heat converts acid forms, so it reports a combined figure |
This is the single most useful thing to know about testing methods. A laboratory using HPLC can tell you how much acid form was present; one using GC cannot, because the instrument itself performs the conversion. It is also why the total on a certificate is calculated with a factor rather than added. See THCa and what heat does to it.
GC coupled to mass spectrometry is standard for residual solvents, where vaporising the sample is exactly what you want.
Differences of a point or more on the same material are routine and usually legitimate:
A good certificate states its measurement uncertainty, which is the laboratory telling you how much of that spread it expects.
Compare figures only between certificates from the same laboratory on the same basis, take small differences as noise, and read the panels rather than ranking products by a decimal place. See what a full contaminant panel covers and a glossary of certificate terms.
Dried bark keeps changing after it is tested. Moisture drifts, light fades the surface, and air slowly oxidizes tannins, which darkens and dulls the color a bath gives. A report describes the bark on the day it was sampled, so the date tells you how far the bag in your hands may have moved since.
A contaminant panel for dried botanical material usually checks four heavy metals (lead, arsenic, cadmium, mercury), microbial counts such as total aerobic count and yeast and mold, pesticide residues, moisture and foreign matter. Each matters for bark you weigh, sift and handle by hand, and each figure only means something next to its method and units.
A botanical certificate of analysis uses a small working vocabulary: LOD and LOQ set what a method can see and measure, ND means nothing was found above that level, ppm and ppb express tiny amounts, and CFU/g counts living microbes. Knowing these terms lets you read any bark report in minutes.
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