Semiquantitative Screening of THC Analogues by Silica Gel TLC with an Ag(I) Retention Zone and Chromogenic Smartphone Detection

Abstract

With the ever-evolving cannabis industry, low-cost and high-throughput analytical methods for cannabinoids are urgently needed. Normally, (potentially) psychoactive cannabinoids, typically represented by Δ9-tetrahydrocannabinol (Δ9-THC), and nonpsychoactive cannabinoids with therapeutic benefits, typically represented by cannabidiol (CBD), are the target analytes. Structurally, the former (tetrahydrocannabinolic acid (THCA), cannabinol (CBN), and THC) have one olefinic double bond and the latter (cannabidiolic acid (CBDA), cannabigerol (CBG), and CBD) have two, which results in different affinities toward Ag­(I) ions. Thus, a silica gel thin-layer chromatography (TLC) plate with the lower third impregnated with Ag­(I) ions enabled within minutes a digital chromatographic separation of strongly retained CBD analogues and poorly retained THC analogues. The resolution (R s) between the closest two spots from the two groups was 4.7, which is almost 8 times higher than the resolution on unmodified TLC. After applying Fast Blue BB as a chromogenic reagent, smartphone-based color analysis enabled semiquantification of the total percentage of THC analogues (with a limit of detection (LOD) of 11 ng for THC, 54 ng for CBN, and 50 ng for THCA when the loaded volume is 1.0 μL). The method was validated by analyzing mixed cannabis extracts and cannabis extracts. The results correlated with those of high-performance liquid chromatography with ultraviolet detection (HPLC-UV) (R 2 = 0.97), but the TLC approach had the advantages of multi-minute analysis time, high throughput, low solvent consumption, portability, and ease of interpretation. In a desiccator, Ag­(I)-TLC plates can be stored for at least 3 months. Therefore, this method would allow rapid distinction between high and low THC varieties of cannabis, with the potential for on-site applicability.

Argentination: A Silver Bullet for Cannabinoid Separation by Differential Mobility Spectrometry

“…45 However, our attempts to add Δ 8 -THC to this workflow resulted in its coelution with CBD using various chemical modifiers (Figures S2 and S3), indicating that an alternative separation strategy will be required. The successful separation of cannabinoids by flash chromatography employing Ag +impregnated silica implies that argentination could be a viable approach, 57 prompting us to investigate the potential of DMS to separate cannabinoids as [M + Ag] + adducts.…”

Extraction solvent selection for Cannabis sativa L. by efficient exploration of cannabinoid selectivity and phytochemical diversity

“…During method development, it was observed that when neat FBBBS solution was used, the spots for particular cannabinoids were very faint, notably for THCA and CBE. Better colour development was then achieved when the plate was made alkaline after FBBBS derivatisation, as has been pointed out elsewhere 26,52 . The best results were obtained when a NaOH 0.1 M solution in MeOH/water 90:10 (v/v) was sprayed after FBBBS.…”

“…However, among the few other reported HPTLC methods for C. sativa inflorescences, 30 most are targeting cannabinoid quantitation, such as the reports by Fischedick et al, 36 Duffau et al, 39 Liu et al, 50 and application notes by CAMAG 38,40 . Some recent studies employing the classical TLC format have also been published for cannabis, aiming to improve resolution or selectivity for cannabinoids 51,52 …”

“…38,40 Some recent studies employing the classical TLC format have also been published for cannabis, aiming to improve resolution or selectivity for cannabinoids. 51,52 The main objective of the present work was to develop extract fingerprints with a balanced band distribution across the chromatogram, while preserving a dedicated elution window for cannabinoids and, at the same time, adequate resolution within them. It was readily observed that balanced separation of both neutral and acidic cannabinoids within a single development is particularly challenging, especially for normal-phase HPTLC.…”

“…Better colour development was then achieved when the plate was made alkaline after FBBBS derivatisation, as has been pointed out elsewhere. 26,52 The best results were obtained when a NaOH 0.1 M solution in MeOH/water 90:10 (v/v) was sprayed after FBBBS. This also effectively avoids the use of the more toxic diethylamine, which is described in the method of UNODC.…”