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Investigation on cannabinoids in Δ8-THC Distillates BY PHARMALABS
- Δ8-THC distillates are becoming a predominant product in the hemp industry. With the legalization of hemp derived products, it is to be expected that these products, as well as other minor-cannabinoids enriched distillates, will increase their market share.
- For this reason, it is of crucial importance that analytical laboratories develop testing methods suitable for this novel sample type.
- Δ8-THC distillates, and most likely also the future concentrates based on other cannabinoids, pose a unique challenge to current testing methods since it appears that during the conversion process into Δ8-THC other THC isomers are formed. These isomers were not commonly found in plant extracts and may interfere with analytes detection in the current analytical methods that were not designed to take them into account.
Δ9-THC Interference vs Peak
- One of the most critical questions raised when analyzing Δ8-THC distillates is whether or not they contain also Δ9-THC.
- In the chromatograms of most Δ8-THC distillates a secondary peak eluting earlier than Δ8-THC can be seen. The retention time of this secondary peak is very similar to that of Δ9-THC and, in most cases, it is identified as such by testing laboratories.
- We were suspicious of this identification since the peak seemed slightly shifted and decided it was necessary to further investigate whether the peak is Δ9-THC or some other isomer.
- The first step was to optimize our methods to better resolve the peaks around Tetrahydrocannabinol.
- The new method allowed us to show, at least in some samples, a retention time shift between the peak of Δ9-THC in the reference standard and the peak under investigation, while the same shift couldn’t be observed for Δ8-THC, as shown in figure 1. Investigation on cannabinoids in Δ8-THC Distillates Page 2 of 5 Issued: 7/24/2020
Figure 1. Overlay of a Δ8-THC Distillate and reference standards.
- The fact that a chromatographic separation was possible seems to suggest that the peak observed in the samples should be attributed to a different isomer and not Δ9-THC.
- Interestingly, in a few samples the un-identified peak matches the retention time of Δ9-THC reference standard, as shown in figure 2, indicating that not all Δ8-THC distillates are the same and that the peak identification should be verified in a case by case basis.
Figure 2. Overlay of a Δ8-THC sample containing also Δ9-THC and reference standard.
- The ability of the method to correctly identify Δ9-THC when present reinforces, in our opinion, the notion that the peak should not be identified as Δ9-THC when the retention times do not match.
- Unfortunately, the separation is hard to achieve and most methods currently in use probably do not allow to appreciate such a minute difference since they were not designed to take this issue into consideration.
- A simple and cost-effective way to discriminate between molecules in UV-Vis detector is to use a Diode Array Detector and analyze the UV absorption spectrum.
- While this approach certainly has its merits and has been widely and successfully applied in the analysis of cannabinoids, we fear that some isomers might be difficult to discriminate in this manner.
- Figure 3. UV spectra in the range 190-400 nm obtained in acidic and basic HPLC Systems. Readapted from Hazekamp at al 2005 1
- Already in the case of Δ8 and Δ9 the DAD spectra are quite similar, and practically indistinguishable in an acidic environment, as shown by Hazekamp et al.1 and reported in figure 3.
- In analytical chemistry the mass spectrometry is considered one of the gold standards for identifying chemical compounds, in particular when chromatographic separation is challenging.
- Unfortunately, in the case of cannabinoid even mass spectrometric identification might prove difficult since different isomers are characterized by the same fragments and are distinguishable only by their relative abundance2.
- Interestingly, Δ8 and Δ9-THC, being closely related, show the same mass spectra at low collision energy and can be differentiated only at normalized collision energy above 40 by the transition 313.2173 -> 191.10783. Investigation on cannabinoids in Δ8-THC Distillates Page 4 of 5 Issued: 7/24/2020
Figure 4. Mass Spectra data of major cannabinoids. C and F show Δ9-THC and Δ8-THC respectively demonstrating the close similarity in the spectrum of THC isomers. Adapted from Bermar et al. 20183.
Since we suspect that the unidentified peak is another isomer of Δ9-THC, it is likely that its discrimination via mass spectrometry will not be trivial and most likely will require a prior chromatographic separation of the peaks.
Conclusion and future work
- The next steps of this investigation into the nature of the un-identified peak will be to analyze a sample spiked with Δ9-THC, to verify if the two peaks can be distinguished.
- Additionally, a mass spectrometry analysis can be attempted, but the close chemistry of the compounds of interest requires an extremely well-tuned method.
- For the time being we believe that there is sufficient proof already to at least question the indiscriminate identification of the unknown peak as Δ9-THC.
1 A. Hazekamp, A. Peltenburg, R. Verpoorte & C. Giroud. (2005). Chromatographic and Spectroscopic Data of Cannabinoids from Cannabis sativa L. - J LIQ CHROMATOGR RELAT TECHNO. 28. 2361-2382.
2 D. J. Harvey (1987). Mass Spectrometry of the cannabinoids their metabolites. – Mass Spectrometry Reviews, 6, 135-229.
3 P. Berman, K. Futoran, G. M. Lewitus, D. Mukha, M. Benami, T. Shlomi & D. Meiri.