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.
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 cannabinoids in marijuana and hemp plant material, oils, extracts, and distillates (1–10). I feel the need to write this column because of misconceptions I hear stated by laypeople and experts in the cannabis industry. I have heard PhD scientists say that spectroscopy is “not quantitative.” This is of course nonsense since an equation called Beer’s Law (see “Spectroscopy” section further on) tells us spectroscopy is quantitative, and a shock to me considering I have written a book on quantitative spectroscopy (11). On the other hand, I have heard people berate chromatography by saying it “doesn’t work.” Chromatography does work for cannabinoid analysis as has been proven in the peer-reviewed literature (2,3 and references therein), and in the right hands produces accurate numbers. To try and clear the air, 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.
The Golden Triangle of Chemical Analysis
The goal of any chemical analysis method is to obtain the greatest accuracy, with the fastest speed, at the lowest cost. These three criteria comprise what has been called the golden triangle of chemical analysis, as seen in Figure 1 (for the definition of accuracy please see my previous column ).
Note that the criteria are located at the corners of the triangle because they are too often mutually exclusive. For example, many techniques may be accurate but might be slow or expensive to use. On the other hand, techniques that are fast and inexpensive are frequently not as accurate as other available technologies. This is seen when comparing laboratory testing to field testing. Many laboratory instruments may require special utilities like cooling water or nitrogen gas, may be sensitive to temperature, humidity, or vibrations, may be too large to be taken outside the laboratory, or require a trained technician or scientist to be utilized. Thus, these instruments are not necessarily fast or inexpensive to operate, but they will often have the highest accuracy. On the other hand, field testing instruments tend to be fast, inexpensive, and operable by laypeople, but are not as accurate as laboratory testing because of the challenges of performing chemical analyses outside the laboratory. This is reflected in Figure 1 where lab testing is near the accuracy corner, while field testing is listed at the bottom near speed and cost.
- 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).