NMR Spectroscopy: Producing a chemical fingerprint of cannabis
Characterizing the chemical makeup of cannabis certainly remains one of the key challenges in the industry, and one technique to consider is nuclear magnetic resonance (NMR) spectroscopy. Although anyone who took organic chemistry in my era remembers NMR as complicated to understand, operate and analyze, today’s technology makes it much easier to use and to generate data. Even better, a range of tools helps the user understand what the data mean. Those factors could determine how wide spread NMR’s use will be in the cannabis industry. Few of the people who could make use of NMR will be organic chemists, but they don’t need to be. Researchers believe that NMR has the potential to enable rapid chemical profiling of cannabis to determine, for example, the levels of cannabidiol (CBD) vs. tetrahydrocannabinol (THC) in a cannabis sample.
“NMR is an information rich method, so we can get a fingerprint of the chemical profiles of the cannabis plant,” says Peter de B. Harrington, Director of the Center for Intelligent Chemical Instrumentation at Ohio University. “Then by using pattern recognition, we are able to differentiate cultivars of cannabis.” Harrington and his colleagues test cannabis extracts with NMR. “The reason is that it is very fast and stable,” he says.
More time saving comes in the analysis of the data. “The idea is that by not quantifying the individual peaks, which is the metabolomic approach, but relying on the NMR spectrum as a fingerprint, much time and cost can be saved,” Harrington explains. “Then, through pattern recognition, we can find key peaks that correspond to the pharmacological properties, the geographical location, strain, and hybrid, or quality.” After the scientists locate those peaks from hundreds in NMR data, they can be quantified.
To make it easier to locate and quantify the desired peaks, Harrington and one of his graduate students, Xinyi Wang, developed a method to enhance the NMR signal. Most NMR work focuses on the absorbance spectrum, which uses about half of the information, and that limits the ability to quantify it. Instead, Wang and Harrington used the NMR’s magnitude spectrum. Then, they used six different approaches to pattern recognition, and 23 out of 24 tests provided results that equaled or bettered those from the magnitude spectrum. Consequently, they wrote: “For pattern recognition of NMR spectra, the magnitude spectrum is advocated.” In a second paper by Wang, a high-throughput method was developed that extracts the cannabis compounds directly into deuterated chloroform that can be directly measured by NMR. The two projects were funded by Chemical Mapping.
For Harrington and his colleagues, NMR provides a fast and effective tool to analyze cannabis in many ways. “The key potential is to provide a fast method for authentication of botanical materials and evaluate the quality of the product,” Harrington explains. “Furthermore, it can be used to guide consumers to the correct product that will provide the desired effect.” Beyond those applications, law-enforcement agencies could use NMR to determine the source of a cannabis sample, revealing if it was grown in a legal or illegal location. In wrapping up, Harrington says, “There are many potential benefits of using NMR in this research area.”