Cannabis and hemp have attracted worldwide popularity as agricultural products. They find their use in anything from medicinal products to clothing fibers. Despite the two plants sharing similar traits, the United States Department of Agriculture (USDA) defines hemp as having less than 0.3 percent tetrahydrocannabinol (THC) in the dry weight of the product. The reliable estimation of THC content in hemp or cannabis needs a method that can accurately measure the water content. Presently, many laboratories are using the loss on drying (LOD) method to estimate the water content. The method measures all volatile components that are driven off by heating and thereby overestimates the water present in the sample. This approach can lead to an underestimation of the actual THC concentration in the product and can further result in its incorrect classification as hemp rather than cannabis. This wrong categorization of the product can potentially lead to fines or the farmer or processor being forced to destroy a crop.
This application note provides a rapid Karl Fischer titration method for the specific determination of water content, using a Karl Fischer oven connected to the titration system.
Coulometry without diaphragm (KF Oven)
1-Component volumetric titration (KF Oven)
2-Component volumetric titration (KF Oven)
Results: Coulometric titration
Sample 3 was spiked with 1% water standard for oven applications (1.88054) as shown in the table below. Percent recovery of the spiked water was calculated and was found to be 100%.
Titration of water in hemp samples was demonstrated by coulometric Karl Fischer titration using a Karl Fischer Oven. Samples were titrated in triplicates and showed a good reproducibility.
Sample 3 spiked with a Karl Fischer oven standard showed a 100% recovery.
This technique is recommended for accurate determination of water in hemp and cannabis samples. The water value is then used in the dry weight material calculation to determine the THC content.
The oven technique is preferable over external dilution as it involves all the water being driven off from the sample and its measurement.
The Karl Fischer method is specific to the determination of water, and does not involve any interference and contribution by other volatiles that might be lost during drying to the estimated water value.