The cannabis plant, known for its multifaceted pharmacological properties, presents an array of chemical constituents that can be leveraged for various applications, including therapeutic and recreational use. The complexity of cannabis strains stems from the presence of over 500 unique chemical compounds, among which approximately 100 cannabinoids have garnered significant attention due to their distinct physiological effects. Understanding the cannabinoid profile of cannabis is imperative for both clinical applications and regulatory compliance. Traditional analytical methods, such as gas chromatography (GC) and liquid chromatography (LC), while effective, present limitations that hinder in-field analysis. In this regard, thermal-desorption ion mobility spectroscopy (TD-IMS) emerges as a prospective alternative for preliminary cannabis screening.
Cannabis strains are often classified based on their cannabinoid composition, particularly the ratios of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). The United Nations has delineated cannabis into two primary categories: drug-type strains, which exhibit high levels of THC and possess psychotropic effects, and fiber-type strains, characterized by elevated CBD levels and negligible psychotropic activity. The necessity for accurate characterization of these strains has led to reliance on advanced chromatographic techniques.
Despite the efficacy of GC and LC, challenges persist. GC, for instance, may induce decarboxylation of acidic cannabinoids during thermal analysis, leading to inaccurate quantification unless a derivatization step is incorporated. Conversely, LC analysis, while preserving cannabinoid integrity, necessitates bulky instruments that lack portability, making them unsuitable for on-site analysis.
Ion mobility spectroscopy (IMS) has garnered interest as a portable analytical technique, offering the potential for real-time analysis of cannabis samples. IMS operates on the principle of measuring the time it takes for ions to traverse a drift tube under the influence of an electric field, providing a rapid assessment of chemical composition. However, IMS has previously faced challenges regarding selectivity and sensitivity, particularly when utilized as a standalone method.
Recent investigations by a multidisciplinary team of researchers from Spain have sought to enhance the capabilities of IMS through the implementation of TD-IMS. This approach integrates thermal desorption to facilitate the volatilization of cannabinoids prior to ion mobility analysis, thus preserving the integrity of the chemical profile while maintaining the portable advantages of IMS.
In a comparative study, researchers analyzed 33 distinct cannabis samples employing both TD-IMS and gas chromatography-mass spectrometry (GC-MS) for benchmarking. The TD-IMS output was represented as a plot of peak intensity against reduced ion mobilities (K0), with characteristic K0 values allowing for the identification of specific cannabinoids. The inclusion of nicotinamide as an internal calibrant optimized the protonation process, enhancing selectivity in TD-IMS measurements.
Principal component analysis (PCA) and linear discriminant analysis (LDA) were applied to the spectral data to classify the samples based on their chemotype and cannabinoid content. Results indicated that while TD-IMS displayed some limitations in peak resolution, it successfully distinguished cannabis samples from non-cannabis materials such as horsetail weed, chamomile, and oregano. Notably, the PCA-LDA analysis demonstrated a clear clustering of cannabis samples, reinforcing the method’s potential as a differentiator of chemotypes.
While TD-IMS does not provide the exhaustive detail achievable through GC-MS, its capacity for rapid, on-site differentiation between cannabis and non-cannabis plant material positions it as a promising tool for preliminary screening. The portability of TD-IMS can facilitate immediate testing in various environments, potentially streamlining compliance protocols and enhancing the understanding of cannabis chemistry in real-world applications.
In conclusion, the integration of TD-IMS into cannabis analysis represents a significant advancement in the field, offering a viable alternative for preliminary screening and supporting the ongoing evolution of cannabis research. As the demand for accurate cannabinoid profiling continues to grow, the adaptability and efficiency of TD-IMS could play a pivotal role in shaping the future of cannabis regulation and therapeutic application.
