Determination of cannabinoids in hemp flour, hemp oil cake, hemp tea, and hemp seed pesto Report on the 2025 Proficiency Test of the German Reference Laboratory for Mycotoxins and Plant Toxins

The German National Reference Laboratory (NRL) for Mycotoxins and Plant Toxins organised a proficiency test for the determination of cannabinoids in hemp flour, hemp oil cake, hemp tea, hemp seed pesto and a standard solution. A total of 19 laboratories participated and they could choose from the listed materials to analyse up to four materials plus a standard solution. The determination of CBD, ∆⁹-THC and their acid forms was mandatory for the laboratories while the quantification of 15 minor cannabinoids was voluntary.

For the regulated cannabinoids ∆⁹-THC and THCA, the reproducibility standard deviation RSD_R varied from 15 to 28 % and from 24 to 73 %, respectively, and for the remaining analytes from 13 to 127 %. Across all samples, analytes, and laboratories, on average, 91 % of z‑scores fell within the satisfactory range ().

In an experiment separate from the proficiency test, the mutual interference caused by the close chromatographic appearance of ∆⁹- and ∆⁸-THC was investigated.