Cannabis sativa L., more commonly known as marijuana, has been used for many centuries and is well-known for its psychoactive and therapeutic effects. Its psychoactive compounds known as cannabinoids, are exclusively present in plants of the Cannabis genus. The most important cannabinoids found in C. sativa are Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD). The first is a highly psychoactive substance, while the latter is a non-psychotropic compound.
The methods currently used by law enforcement and the pharmaceutical industry for detection and quantification of cannabinoids consist of colorimetric testing and instrumental methods such as HPLC and GC-MS. Colorimetric methods are low in cost but can have poor selectivity, while instrumental methods are not portable, and produce high operational costs with long analysis times. This work aims are to develop an alternative method that can address the disadvantages of these established methods. For this purpose, a voltammetric method was developed using CV and SWV techniques, with a 3D-printed platform modified with carbon paste and silver ink for use as electrodes. The 3D electrode system was electrochemically characterized, and an analysis of variance (ANOVA) was performed to test its repeatability and reproducibility, yielding good results for both parameters. Detection and quantification of Δ9-THC and CBD were successfully achieved.
The results were compared to two other commercial electrodes, one being a conventional platinum electrode in a three-electrode system with a platinum wire electrode and Ag/AgCl in saturated KCl as the auxiliary and reference electrodes, respectively, and the other being a commercial printed electrode (SPPE). The analytical parameters and average concentrations found for these analytes were similar to those found for the commercial electrodes. Limits of detection (LOD) and quantification (LOQ) were in the µmol L-1 range. Tukey's test was used to demonstrate that means for Δ9-THC concentrations were statistically similar for all three electrodes; similarly the CBD concentrations produced mean values that were statistically similar to the commercial systems. The quantitative results were validated by comparison with by GC-MS, yielding relative error values ranging from 2.3% to 19%. Finally, a cost analysis of the materials used to prepare these electrodes showed an approximate value of US$ 0.32 per unit, representing a saving of approximately 93% compared to the cost of a commercial screen-printed electrode. In conclusion, the developed method and electrode proved promising for the detection and quantification of Δ9-THC and CBD at µmol L-1 levels. The resultant electrode system was versatile, portable, and cost-effective, with significant potential for application in clinical and forensic fields.