A range of cannabis derivatives are commercially available for purchase across the world's markets. Country-to-country, the legality of these products differs. In Europe, products that contain higher levels of THC (tetrahydrocannabinol) than 0.2% are generally prohibited. That said, CBD (cannabidiol) isn't restricted and is actually advertised as offering pharmaceutical benefits.
Advertised benefits of consuming CBD include pain relief, anxiety and depression treatment, cancer-related symptom relief, acne reduction, neuroprotective properties, improved heart health and diabetes prevention.
In this short study, we used the Specac Pearl FTIR transmission spectrometer accessory to compare the FTIR spectra of two such commercial cannabis oils.
Method: How to analyze Cannabis Oil using FTIR
Two commercially available CBD oils, generally used as food supplements, were obtained. Both samples were placed in a 25 µm wedged CaF2 oyster cell. FTIR spectra of cannabis oil was recorded on a commercially available FTIR spectrometer, fitted with a Pearl liquid accessory.
Each oil contained Hemp seed oil and Hemp paste and the lower strength product also contained the ingredient sunflower lecithin.
Results and Discussion: Cannabis Oil infrared Analysis
Figure 1 shows the FTIR spectra recorded for both oil samples. As you might expect, each trace is similar with some small changes that correspond to the contrasts in the chemical compounds present each cannabis oil.
Figure 1: FTIR spectra of two CBD oils, recorded with a 25 µm wedged CaF2 oyster cell.
To more easily detect differences between the samples, another spectrum was obtained, where the spectrum of the 2.75% CBD oil was then subtracted from the spectra of the 5% oil (Figure 2). In a difference spectrum, the positive peaks indicate a higher concentration of absorbing species in the 5% oil than in the 2.75% oil, while the negative peaks indicate a lower or zero concentration.
Figure 2: Difference spectrum showing the 5% CBD oil minus the 2.75% CBD oil (black). Also shown are reference spectra of CBD (red) and linoleic acid (green) for comparison.
Spectral traces for pure CBD (red) and linoleic acid (the major component of sunflower lecithin, green) are also shown. By comparing these spectra to the difference spectrum, it is immediately apparent that the positive peaks in the difference spectrum (highlighted with red arrows) correspond to an increase of CBD, whilst the negative peak (highlighted with a green arrow) corresponds to the C=O stretch from linoleic acid.
By comparing the traces shown in Figure 1 this band is present as a shoulder only in the 2.75% trace, whilst the 5% oil does not exhibit this shoulder. This is because it does not contain sunflower lecithin.
This shoulder is present on the edge of multiple overlapping intense bands at ca. 1740 – 1750 cm-1 present for each sample (albeit in higher quantities for the 5% supplement than the 2.75% as indicated by a positive peak in the difference spectrum). These peaks do not arise from the CBD oil, because the peaks are not present in the red trace shown in Figure 2. Based on their location in the FTIR spectrum, the peaks can be tentatively assigned to fatty acid esters from hemp oil.
CBD includes two peaks at 1628 cm-1 and 1586 cm-1 that can be assigned to a C=C stretch. These peaks can be identified in each trace from Figure 1 (which confirms the presence of CBD in both samples) and would provide ideal candidates for quantification. With the preparation of known calibration standards and the recording of the peak intensity of these two peaks, the preciuse proportion of CBD oil in each oil could be quickly determined. The Pearl and Oyster FTIR system is very much optimized for high throughput analysis and would be ideally suited for such a kind of application.
Summary and Conclusion: Cannabis Oil FTIR Analysis
In conclusion, our results confirm that the 5% CBD oil does in fact contain more CBD than the 2.75% oil. The results also confirm the presence of sunflower lecithin in the 2.75% oil and the absence of this ingredient in the 5% oil.
Reference spectra of pure CBD was obtained from the Georgia State Crime Lab Drug FT-IR Spectral Library.
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