Development and validation of a low-cost spectrophotometric method for cannabidiol (CBD) quantification based on the Beam reaction

Cannabidiol (CBD) is a compound of high pharmacological interest, requiring accessible analytical methods for its identification and measurement. This study proposes the transformation of the classic Beam reaction, traditionally a qualitative colorimetric test, into a robust, low-cost quantitative technique using UV-Vis spectrophotometry. The method is based on the formation of a specific chromophore between CBD/CBDA and a 5% ethanolic KOH solution. Spectral characterization identified a maximum absorbance peak at 530 nm. Kinetic analysis established that the reaction stabilizes after a 24-hour incubation period, ensuring high reproducibility for batch analysis. The optimized protocol demonstrated high linearity (R 2 > 0.99) and excellent precision, with a Relative Standard Deviation (RSD%) of 2.88% for intraday and 4.74% for interday assays. The limit of detection (LOD) and limit of quantification (LOQ) were 1.84 and 5.58 µg/mL respectively. By utilizing widely available reagents and standard instrumentation, this method provides a significant advantage for laboratories and research centers where high-performance liquid chromatography (HPLC) is not feasible. The findings validate the Beam reaction as a precise, simple, and economically viable tool for the quantification of total CBD.