SERS Analysis of Several Cannabinoids

Background

The cannabinoid profile of cannabis-based products must be determined to support label claims and assure product quality. Traditionally, HPLC-MS measurements reveal THC, THCA, CBD, and CBDA quantities, as well as trace cannabinoids such as CBG and CBGA.¹ However, HPLC-MS has certain drawbacks that can be avoided with other techniques such as Raman spectroscopy, which offers sensitivity, selectivity, reduced instrument size, non-destructive sampling, and simple implementation. In this study, we utilize SERS, a variant of Raman spectroscopy, to enable trace level detection of these cannabinoids.

Experimental Conditions

The following analytical grade standards were diluted to 10 ppm in their respective solvents: cannabidiol (CBD), cannabidiolic acid (CBDA), tetrahydrocannabinol (THC), tetrahydrocannabinolic acid (THCA), cannabigerol (CBG), and cannabigerolic acid (CBGA).

Microliter volumes were pipetted into colloidal solutions of gold nanoparticles, and measured with the Ocean Optics QE Pro-Raman+ spectrometer, at 3 seconds integration time, after interrogation with a 785 nm laser at 350 mW laser power.

Results

The SERS spectra of each cannabinoid are presented in Figure 1. Even though there are only slight structural differences between these cannabinoid molecules (i.e., THC and THCA differ by a carboxylic acid group, and THC and CBD differ by a hydroxyl group), the SERS spectra show stark differences due to certain functional groups giving different Raman shifts.

Figure 1: SERS spectra of 10 ppm (a) CBDA, (b) CBD, (c) CBGA, (d) CBG, (e) THCA, and (f) THC.

Conclusions

We present a method to detect trace levels of cannabinoids that utilizes the unique optical properties of gold nanoparticles coupled with surface enhanced Raman spectroscopy

References

[1] Yu, B. Ge, M., Li, P., Xie, Q., and Yang, L. Talanta 2019, 191, 1–10.