Determination of Water in Hemp and Cannabis by Karl Fischer Titration

This article from Issue 12 of the Analytix Reporter, produced by Merck, describes an application that demonstrates a moisture determination method for hemp and cannabis flower that is selective for water, and also provides rapid and accurate test results.

Hemp and cannabis are becoming important agricultural products, and are being increasingly used in medicinal products, cosmetics, foods, oils, and textile fibers around the world. The cannabis market is growing rapidly, mainly due to the use as therapeutics for medical treatments by the pharmaceutical industry.
Water in cannabis and hemp impacts the determination of the potency and must be determined accurately to calculate the correct delta-9 tetrahydrocannabinol
(THC) content of the plant. For this, an accurate method for determining water content must be employed. Loss on drying (LOD) is often used, but this method can simultaneously measure volatile compounds too. However, Karl Fischer Titration is specific to water and the here proposed method provides an accurate method for determining the water content in hemp and cannabis.

Karl Fischer titration based methods are simple to run, but the equipment is a bit more expensive than that used for LOD determination. The advantage of the Karl Fischer titration method is its specificity for water. As a result, the reported water value does not include amounts of other volatile compounds. Two
methods based on the Karl Fischer titration were evaluated ― coulometry with a Karl Fischer oven and a direct volumetric titration with an external extraction.

The Karl Fischer coulometric titration in combination with a Karl Fischer oven provides reproducible results. It prevents an overestimation of water content caused by volatile compounds, as to be considered for the loss on drying method. In addition it requires only a small amount of sample and reagent. The volumetric
Karl Fischer titration with external extraction did not produce reproducible results and is, therefore, not recommended. However, the volumetric Karl Fischer method in combination with a Karl Fischer oven can be employed, but since volumetry is not as sensitive as coulometry, the sample size needs to be increased to get reliable results.

Therefore, it is recommended to use the Karl Fischer oven method with coulometry for water determination in hemp and cannabis to achieve the most accurate results. This enables the exact and precise calculation of the dry weight delta-9 THC concentration.

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*The life science business of Merck operates as MilliporeSigma in the U.S. and Canada.