Both spectroscopy and chromatography have been used for decades to measure the concentrations of molecules in samples, and now both techniques have been used to measure cannabinoid profiles in marijuana and hemp based samples. This column briefly introduces these techniques to the novice, and then using the concepts of speed, cost, and accuracy, analyzes the advantages and disadvantages of each technique for cannabis potency analysis.
Introduction to Chromatography
Chromatography is used to separate a mixture into its individual components. Once the components have been separated, the amount of each component can then be quantified. The word chromatography means “color writing” in Greek because in its original application chromatography was used to separate plant pigments into their separate colors which were viewed during the separation process.
In chromatography the sample to be analyzed is typically in solution. If a liquid needs to be analyzed the sample preparation may be simply a matter of “dilute and shoot” as chromatographers like to say, which means the sample must be diluted enough so that it is in the concentration range where the instrument can quantitate it. So, for example, to prepare a cannabis extract for chromatography, dissolving an appropriate amount in a solvent and diluting it with a further known quantity of solvent may be the only sample preparation needed.
However, the sample preparation for solids, such as cannabis plant material, is more challenging. The sample must be weighed, ground, have solvent added, agitated to promote extraction of the cannabinoids, filtered, and then diluted to the concentration range where the instrument can quantitate it (2). (Note: There have been many cannabis plant material sample preparation methods published, and even more in use. From my experience of monitoring analyses at many cannabis analysis laboratories, the method in reference 2 is best, and I would like to see it become the industry standard.)
Once the sample is in solution it is injected onto a “column” which is essentially a tube filled with a “stationary phase” and a “mobile phase.” The mobile phase can be a gas such as nitrogen or helium, which gives rise to gas chromatography (GC), or a solvent which gives rise to liquid chromatography (LC). The stationary phase is often silica particles that may or may not have a coating on them. The column can be as simple as a glass tube, or as modern as a thin steel pipe capable of withstanding high pressure, hence the technique of high performance liquid chromatography (HPLC). The mobile phase flows through the column carrying the sample molecules with it. For LC gravity can be used to encourage fluid flow, in gas chromatography changes in pressure are used, and in HPLC a pump is used to force fluid through the column.
The separation process for chromatography is illustrated in Figure 2.
- B.C. Smith, Cannabis Science and Technology 1(4), 12–16 (2018).
- M.W. Giese, M.A. Lewis, L. Giese, and K.M. Smith, J. AOAC Int. 98(6), 1503 (2015).
- T. Ruppel and M. Kuffel, “Cannabis Analysis: Potency Testing Identification and Quantification of THC and CBD by GC/FID and GC/MS,” PerkinElmer Application Note (2013).
- B.C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, 2nd Edition (CRC Press, Boca Raton, Florida, 2011).
- C. Sánchez-Carnerero Callado, N. Núñez-Sánchez, S. Casano, and C. Ferreiro-Veraa, Talanta 190, 147–157 (2018).
- B.C. Smith, M. Lewis, and J. Mendez, “Optimization of Cannabis Grows Using Fourier Transform Mid-Infrared Spectroscopy,” PerkinElmer Application Note (2016).
- B.C. Smith, Cannabis Science and Technology 2(6), 28–33 (2019).
- B.C. Smith, Terpenes and Testing Nov.-Dec., 48 (2017).
- B.C. Smith, Terpenes and Testing Jan.-Feb., 32 (2018).
- B.C. Smith, P. Lessard, and R. Pearson, Cannabis Science and Technology 2(1), 48–53 (2019).
- B.C. Smith, Quantitative Spectroscopy: Theory and Practice (Elsevier, Boston, Massachusetts, 2002).
- B.C Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, 2nd Edition (CRC Press, Boca Raton, Florida, 2011).
- D. Shoemaker and C. Garland, Experiments in Physical Chemistry, 2nd Edition (McGraw Hill, New York, New York, 1967).
- California Bureau of Cannabis Control Regulations, Section 5719.
About the Columnist
Brian C. Smith, PhD, is Founder, CEO, and Chief Technical Officer of Big Sur Scientific in Capitola, California. Dr. Smith has more than 40 years of experience as an industrial analytical chemist having worked for such companies as Xeros, IBM, Waters Associates, and Princeton Instruments. For 20 years he ran Spectros Associates, an analytical chemistry training and consulting firm where he improved their chemical analyses. Dr. Smith has written three books on infrared spectroscopy, and earned a PhD in physical chemistry from Dartmouth College.
How to Cite This Article
B.C. Smith, Cannabis Science and Technology 2(6), 10-14 (2019).