The Separation of Cannabinoids on Sub-2 µm Immobilized Polysaccharide Chiral Stationary Phases

Progress in the analysis of phytocannabinoids by HPLC and UPLC (or UHPLC) during 2020-2023

INTRODUCTION

Organic molecules that bind to cannabinoid receptors are known as cannabinoids. These molecules possess pharmacological properties similar to those produced by Cannabis sativa L. High-performance liquid chromatography (HPLC) and ultra-performance liquid chromatography (UPLC, also known as ultra-high-performance liquid chromatography, UHPLC) have become the most widely used analytical tools for detection and quantification of phytocannabinoids in various matrices. HPLC and UPLC (or UHPLC) are usually coupled to an ultraviolet (UV), photodiode array (PDA), or mass spectrometric (MS) detector.

OBJECTIVE

To critically appraise the literature on the application of HPLC and UPLC (or UHPLC) methods for the analysis of phytocannabinoids published from January 2020 to December 2023.

METHODOLOGY

An extensive literature search was conducted using Web of Science, PubMed, and Google Scholar and published materials including relevant books. In various combinations, using cannabinoid in all combinations, cannabis, hemp, hashish, C. sativa, marijuana, analysis, HPLC, UHPLC, UPLC, and quantitative, qualitative, and quality control were used as the keywords for the literature search.

RESULTS

Several HPLC- and UPLC (or UHPLC)-based methods for the analysis of phytocannabinoids were reported. While simple HPLC-UV or HPLC-PDA-based methods were common, the use of HPLC-MS, HPLC-MS/MS, UPLC (or UHPLC)-PDA, UPLC (or UHPLC)-MS, and UPLC (or UHPLC)-MS/MS was also reported. Applications of mathematical and computational models for optimization of protocols were noted. Pre-analyses included various environmentally friendly extraction protocols.

CONCLUSION

During the last 4 years, HPLC and UPLC (or UHPLC) remained the main analytical tools for phytocannabinoid analysis in different matrices.

Liquid electron ionization-mass spectrometry as a novel strategy for integrating normal-phase liquid chromatography with low and high-resolution mass spectrometry

Normal-phase liquid chromatography (NPLC) plays a pivotal role in the rapid separation of non-polar compounds, facilitating isomer separation and finding applications in various crucial areas where aprotic solvents are necessary. Similar to reversed-phase liquid chromatography (RPLC), NPLC requires a robust and sensitive detector to unequivocally identify the analytes, such as a mass spectrometer. However, coupling NPLC with mass spectrometry (MS) poses challenges due to the incompatibility between the non-polar solvents used as the mobile phase and the primary ionization techniques employed in MS. Several analytical methods have been developed to combine NPLC with electrospray ionization (ESI), but these methods are restricted to the analysis of polar compounds. In most cases, atmospheric pressure chemical ionization (APCI) becomes necessary to expand the range of analysis applications. To overcome these limitations and fully realize the potential of NPLC-MS coupling, a technique termed liquid electron ionization-mass spectrometry (LEI-MS) can be used. LEI-MS offers a straightforward solution by enabling the effective coupling of NPLC with both low and high-resolution MS. LEI allows for the comprehensive analysis of non-polar compounds and provides a powerful tool for isomer separation and precise identification of analytes. Optimal separations, mass spectral qualities, and matches with the NIST library were obtained in both configurations, demonstrating the potential of the proposed approach.

Bidimensional heart-cut achiral-chiral liquid chromatography coupled to high-resolution mass spectrometry for the separation of the main chiral phytocannabinoids and enantiomerization studies of cannabichromene and cannabichromenic acid

In this work, a heart-cut bidimensional achiral-chiral liquid chromatography method coupled to high-resolution mass spectrometry was developed for the separation of the main carboxylated phytocannabinoids, namely cannabidiolic acid (CBDA), tetrahydrocannabinolic acid (THCA), cannabichromenic acid (CBCA), and cannabicyclolic acid (CBLA), and decarboxylated derivatives, namely cannabidiol (CBD), Δ9-tetrahydrocannabinol (Δ9-THC), cannabichromene (CBC), and cannabicyclol (CBL), and the evaluation of their enantiomeric composition in extracts of different Cannabis sativa L. varieties. Optimal conditions for the chiral analysis of CBC- and CBL-type compounds were found with methanol and water (95:5, v/v, with 0.1% formic acid, 1.5 mL/min) on an amylose-based chiral stationary phase. These settings also allowed to evaluate the parameters responsible for CBC and CBCA racemization.

Recent advances in chiral selectors immobilization and chiral mobile phase additives in liquid chromatographic enantio-separations: A review

For decades now, the separation of chiral enantiomers of drugs has been gaining the interest and attention of researchers. In 1991, the first guidelines for development of chiral drugs were firstly released by the US-FDA. Since then, the development in chromatographic enantioseparation tools has been fast and variable, aiming at creating a suitable environment where the physically and chemically identical enantiomers can be separated. Among those tools, the immobilization of chiral selectors (CS) on different stationary phases and the chiral mobile phase additives (CMPA) which have been progressed and studied extensively. This review article highlights the major advances in immobilization of CS together with their different recognition mechanisms as well as CMPA as a cheaper and successful alternative for chiral stationary phases. Moreover, the role of molecular modeling tool as a pre-step in the choice of CS for evaluating possible interactions with different ligands has been pointed up. Illustrations of reported methods and updates for immobilized CS and CMPA have been included.

Enantioseparation of chiral phytocannabinoids in medicinal cannabis

The evaluation of the chiral composition of phytocannabinoids in the cannabis plant is particularly important as the pharmacological effects of the (+) and (-) enantiomers of these compounds are completely different. Chromatographic attempts to assess the presence of the minor (+) enantiomers of the main phytocannabinoids, cannabidiolic acid (CBDA) and trans-Δ⁹-tetrahydrocannabinolic acid (trans-Δ⁹-THCA), were carried out on heated plant extracts for the determination of the corresponding decarboxylated species, cannabidiol (CBD) and trans-Δ⁹-tetrahydrocannabinol (trans-Δ⁹-THC), respectively. This process produces an altered phytocannabinoid composition with several new and unknown decomposition products. The present work reports for the first time the stereoselective synthesis of the pure (+) enantiomers of the main phytocannabinoids, trans-CBDA, trans-Δ⁹-THCA, trans-CBD and trans-Δ⁹-THC, and the development and optimization of an achiral-chiral liquid chromatography method coupled to UV and high-resolution mass spectrometry detection in reversed phase conditions (RP-HPLC-UV-HRMS) for the isolation of the single compounds and evaluation of their actual enantiomeric composition in plant. The isolation of the peaks with the achiral stationary phase ensured the absence of interferences that could potentially co-elute with the analytes of interest in the chiral analysis. The method applied to the Italian medicinal cannabis variety FM2 revealed no trace of the (+) enantiomers for all phytocannabinoids under investigation before and after decarboxylation, thus suggesting that the extraction procedure does not lead to an inversion of configuration.

Chiral Separation of Cannabichromene, Cannabicyclol, and Their Acidic Analogs on Polysaccharide Chiral Stationary Phases

Until recently, chirality has not been a major focus in the study of cannabinoids, as most cannabinoids of interest, such as cannabidiol and tetrahydrocannabinol, exist as a single isomer from natural sources. However, this is changing as more cannabinoids are identified, and compounds such as cannabichromene and cannabicyclol are emerging as potential investigatory candidates for varying indications. Because these molecules are chiral, the separation and study of the individual enantiomers' biological and physiological effects should therefore be of interest. The purpose of this study was to identify analytical separation conditions and then adapt those conditions to preparative separation. This was accomplished with a column-screening approach on Daicel's immobilized polysaccharide chiral stationary phases using non-traditional mobile phases, which included dichloromethane, ethyl acetate, and methyl tert-butyl ether under high-performance liquid chromatography conditions. CHIRALPAK^® IK was found to separate all four compounds well with mobile phases containing hexane-dichloromethane (with or without an acidic additive). From these methods, the separation productivities were calculated to better visualize the separation scalability, which shows that the kilogram-scale separations of each are feasible.

Recent challenges and trends in forensic analysis: Δ9-THC isomers pharmacology, toxicology and analysis

Δ9-tetrahydrocannabinol (Δ9-THC) isomers, especially Δ8-tetrahydrocannabinol (Δ8-THC), are increasing in foods, beverages, and e-cigarettes liquids. A major factor is passage of the Agriculture Improvement Act (AIA) that removed hemp containing less than 0.3 % Δ9-THC from the definition of "marijuana" or cannabis. CBD-rich hemp flooded the market resulting in excess product that could be subjected to CBD cyclization to produce Δ8-THC. This process utilizes strong acid and yields toxic byproducts that frequently are not removed prior to sale and are currently inadequately studied. Pharmacological activity is qualitatively similar for Δ8-THC and Δ9-THC, but most preclinical studies in mice, rats, and monkeys documented greater ∆9-THC potency. Both isomers caused graded dose-response effects on euphoria, blurred vision, mental confusion and lethargy, although Δ8-THC was at least 25 % less potent. The most common analytical methodologies providing baseline resolution of ∆8-THC and ∆9-THC in non-biological matrices are liquid-chromatography coupled to diode-array detection (LC-DAD or LC-PDA), while liquid chromatography coupled to mass spectrometry is preferred for biological matrices. Other available analytical methods are gas-chromatography-mass spectrometry (GC-MS) and quantitative nuclear magnetic resonance (QNMR). Current knowledge on the pharmacology of ∆8-THC and other ∆9-THC isomers are reviewed to raise awareness of the activity of these isomers in cannabis products, as well as analytical methods to discriminate ∆9-THC qualitatively, and quantitatively and ∆8-THC in biological and non-biological matrices.

Characteristic and complementary chiral recognition ability of four recently developed immobilized chiral stationary phases based on amylose and cellulose phenyl carbamates and benzoates

To date, various immobilized chiral stationary phases (CSPs) have been developed. The immobilized CSPs have opened up possibilities not only maintaining the high chiral recognition abilities as well as corresponding coated ones but also affording high durability to various mobile phase. This report directed to investigate enantioseparation of recently launched four immobilized CSPs with cellulose and amylose backbones under normal phase liquid chromatography conditions. Their chiral recognition abilities were compared with previously developed six immobilized CSPs. Particularly, we focused on the complementarity for chiral recognitions. Among them, amylose tris(3‐chloro‐5‐methylphenylcarbamate) CSP, namely, CHIRALPAK IG, showed notable chiral recognition abilities to various racemates. As expected, the investigated immobilized CSPs represented remarkable durability to wide range of mobile phases, whereas the corresponding coated CSPs could not be run due to the irreversible degradation. Taking advantage of unrestricted solvent compatibility, chiral separation selectivities were improved for some racemates.