Validated Cannabis Analysis with HPLC-DAD
As the need for cannabis analysis increases, labs need easier and more complete methods of testing samples. As Paula N. Brown, President of the Natural Health Product Research Society of Canada and Director of Applied Research for Natural Health & Food Products at the British Columbia Institute of Technology, and her colleagues wrote: “There is an explosion in the number of labs analyzing cannabinoids in marijuana (Cannabis sativa L., Cannabaceae) but existing methods are inefficient, require expert analysts, and use large volumes of potentially environmentally damaging solvents.”1
Many of today’s cannabis-analysis labs use gas chromatography with a flame ionization detector (GC-FID) or high-performance liquid chromatography with a diode array detector (HPLC-DAD). “GC-FID is an older technique that is becoming less common for cannabinoid analysis,” Brown says. “The reason is that it cannot directly measure the acidic cannabinoids.” So, GC-FID measures tetrahydrocannabinol (THC) and cannabidiol (CBD), but not THCA and CBDA. With a chemical conversion—derivatization—GC-FID can measure all of these. “The advantage of HPLC is that you can measure both directly, with taking any extra derivatization step,” Brown explains. “This makes the assay simpler and easier, which is important for efficiency.”
Although an experienced chemist can handle derivatization relatively easily, that does not describe everyone testing cannabis samples. And as Brown notes, “With every step you have a potential loss of accuracy.” Plus, Brown points out that even with many published GC-FID and HPLC-DAD methods that are used often, “few, if any, of these methods were validated.”
So, Brown and her colleagues published their validated HPLC-DAD method. “Validation is the process by which you determine how your method performs,” Brown explains. “Is it accurate, precise and does it work the same way every time you run the assay?”
When a label claims that a product contains a specific amount of THC or CBD, for example, a customer can only trust that number if a validated test was used by experienced technicians. “Methods used in determining product specifications must be suitable for their intended use,” Browns points out. “Determining method suitability—often called ‘fitness’—is done by conducting a validation.”
In describing the highlights of this work, Brown notes that it is easier, faster and uses less toxic solvents than other methods. Plus, it measures neutral and acidic cannabinoids. As she concludes: “It is fully validated, so we know how it will perform—accuracy, precision, detection and quantification limits, etc.”
Although the research noted here only applied HPLC-DAD to cannabinoids. “There are other measures that should be considered when establishing the quality and safety of medical cannabis, including pesticides, microbials, alflatoxins and heavy metals,” Brown explains. “In addition to cannabinoids, terpenes are typically measured as well.”
In their conclusion about this HPLC-DAD method, Brown and her colleagues wrote: “This method can be used in a variety of settings from clinical studies, research, quality control, and regulatory evaluation of this growing industry.”
Developing techniques that provide the needed testing and accuracy, but with easier and greener methods could make a big difference in the cannabis industry, especially given the limited experience of the some of the companies.
1. Mudge, E.M., Murch, S.J., and Brown, P.N. 2017. Leaner and greener analysis of cannabinoids, Anal. Bioanal. Chem. 409:3153–3163.