Abstract :
[en] Cannabis has now been the center of scientific attention for several years. Indeed, since its pharmacological potential was rediscovered in the 2000s, this plant has become a major subject in research laboratories, leading to the publication of countless scientific works. In the field of analytical chemistry, various methods of analyzing cannabinoids in cannabis samples have been published. For this purpose, various techniques have been applied, but liquid and gas chromatography are undoubtedly the most used. However, in recent years, other techniques, equally interesting from the point of view of analytical performance, have been successfully implemented in analytical laboratories.
This thesis project aims to investigate the potential of rapidly developing techniques for the analysis of cannabinoids in cannabis samples. In particular, two techniques were involved in the research discussed in this thesis: near-infrared spectroscopy (NIR) and supercritical fluid chromatography (SFC). These two techniques have been identified as particularly promising. NIR spectroscopy allows samples to be analyzed quickly and directly in their original form. Indeed, the preparation of samples is most often not required by the technique, representing a considerable advantage in terms of time but also economic. In addition, the components of the spectrophotometer can be miniaturized, an aspect that has enabled the development of portable spectrophotometers, which offer the possibility of carrying out analyses directly in the field. This possibility was therefore studied in the specific case of the analysis of cannabis samples to determine their ∆9-tetrahydrocannabinol (THC) content. Two portable spectrophotometers with different technical characteristics were tested first on cannabis inflorescences and then on resins in order to choose the most suitable device for this type of analysis. The results obtained during this preliminary study demonstrated the applicability of portable NIR spectroscopy for the quantitative analysis of THC in cannabis samples, without any preparation process.
In the case of SFC, this analytical technique can be considered as an evolution of liquid chromatography, with several advantages over the latter. Indeed, if the analytical performance in terms of efficiency is comparable to that of ultra-high-performance liquid chromatography (UHPLC), the use of organic solvents and analysis times can be drastically reduced, depending on the operating conditions chosen. During this thesis, an SFC-UV method was developed and applied to the quantitative analysis of five cannabinoids on 92 real cannabis samples, with the aim of evaluating the quantitative potential of this technique. The results were then compared with those obtained using a reference method based on UHPLC-UV. The Bland-Altman statistical method was then applied and the “difference plots” confirmed the concordance of the results obtained with both techniques, thus demonstrating the equivalence of SFC for the analysis of cannabinoids.
In addition to the technological advances in cannabinoid analysis, this thesis project also covered the methodological aspects of the development of analytical methods. Indeed, the principles of "analytical quality by design" (AQbD) have been deepened by means of a review of its applications for pharmaceutical quality control, presented by the scientific literature. This approach, based on a thorough investigation of operational parameters, allows the development of robust and efficient analytical methods. Operational choices are made through statistical evaluations, which allow the identification and optimization of critical methodological parameters for certain quality attributes of the analytical method under development. The result of this approach is a “method operable design region”, consisting in a multidimensional region exhibiting a series of operating conditions, which allow to satisfy the quality requirements of the method, with a known probability. Within this multidimensional space, which can be seen as a robustness space, the operational parameters of the method can be selected.
In this context, this innovative approach was evaluated by means of two scientific papers. The first concerned the optimization of an analytical method based on liquid chromatography for monitoring THC concentrations in oily cannabis extracts. This work made it possible to apply this strategy and to study its advantages closely. The second work focused on the application of this strategy to an unusual and innovative analytical technique: surface enhanced Raman scattering (SERS). Indeed, the scientific literature shows a wide application of AQbD for the development of methods based on separation techniques, such as capillary electrophoresis and liquid chromatography for example. However, their application to analytical methods based on spectroscopic techniques is insufficiently described. For these reasons, in the last part of this work, the AQbD approach was applied, for the first time, to SERS, which is gradually spreading in analytical laboratories.
