Portable electrochemical sensoristic system for the on-site measurement of cannabinoids

In recent years, the EU common agricultural policy has provided subsidies for the cultivation of certain varieties of the Cannabis sativa L. plant for industrial uses, provided the principal psychoactive constituent, ∆9-tetrahydrocannabinol (∆9-THC), does not exceed 0.3% w/w [1]. Moreover, in many countries, C. sativa derivatives such as oils, biscuits, and even dried parts of the plant can be freely sold. However, in freely commercialized products it is not uncommon to find ∆9-THC concentrations exceeding the legal limit. Therefore, accurate controls to meet specific regulations are mandatory. The analysis of cannabinoids such as ∆9-THC, cannabidiol (CBD) and their natural acidic precursors (i.e. ∆9-THCA and CBDA), in C. sativa samples (female inflorescences) is usually carried out by chromatographic techniques [2-4]. However, the equipment cost, the reagent consuming sample preparation, the need for trained personnel, and long analysis times are remarkable drawbacks, preventing their use insitu. As promising alternatives to these techniques in allowing real-time and fast cannabinoid screening, electrochemical sensors have been receiving considerable interest, thanks to their low cost, handiness, and miniaturization possibility [5]. In fact, ∆9-THC, CBD, ∆9-THCA and CBDA are electroactive, due to the oxidation of the phenolic group, which makes them good candidates for electrochemical analysis. Our research group has recently demonstrated that screen printed electrodes (SPEs), modified with a carbon black (CB) coating, can be used for the fast quantification of Δ9-THCA in recreational type C. sativa extracts [6] and, using a multivariate approach, for the correct classification of most C. sativa samples into the classes of legal and illegal samples according to total Δ9-THC content [7]. The obtained results suggest the possibility to consider the proposed method as a starting point for the implementation of an automated device for rapid pre-screening of total Δ9-THC content directly on site. The design of a portable device for on-field measurements represents the final stage in the configuration of a sensor system. The ideal device should facilitate all stages of analysis, from weighing the sample to recording the relevant electrochemical signal, in order to minimise and simplify the operations required by the operator. This study describes the developed measuring system prototype and the measurement principle. It also illustrates the proposed measurement procedure and the experimental activities performed for its preliminary verification.