Portable voltammetric method for the simultaneous determination of Δ9-Tetrahydrocannabinol and cannabidiol in alkaline medium using unmodified screen-printed carbon electrodes

Simultaneous detection of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) is crucial for the analysis of seized materials and cannabis-based preparations. To address this need, a simple, rapid, and selective electrochemical method was developed for the preliminary detection and quantification of both cannabinoids. The proposed method employs unmodified carbon screen-printed electrodes (carbon-SPEs) in a strongly alkaline medium (0.5 mol L^-1 NaOH solution). The electrochemical behaviors of THC and CBD were investigated over a wide range of pH values, enabling a simultaneous detection with distinct peak potentials observed on carbon-SPE (vs Ag). THC exhibited a single irreversible oxidation process (O_1T) on the carbon-SPE surface, whereas CBD showed, for the first time, five well-defined electrochemical processes, with two reduction processes (R_1C and R_2C) and three oxidation processes (O_1C, O_2C and O_3C). Square wave voltammetric technique was optimized for the simultaneous determination of THC and CBD using their oxidation processes at O_1T and O_3C on carbon-SPE, with limits of detection of 0.09 μmol L^-1 and 2.72 μmol L^-1, respectively. Moreover, consistent electrochemical responses were obtained using either the same (N = 5) or different SPEs (N = 3), with RSDs lower than 5.6% and 2.0 % for peak currents and peak potentials, respectively. Method applicability was confirmed by analyzing thirty-five (35) real seized samples and seven cannabis-based products, showing good agreement with GC-MS results. Addition-recovery studies using real seized samples yielded values close to 100 % for both analytes: 102 ± 2 % for O_1T (THC) and 103.3 ± 0.8 % for O_3C (CBD). These findings highlight the method's potential as a reliable, low-cost, and field-deployable tool for forensic screening and quality control in cannabis-derived products.