How Standardized Sample Preparation Can Solve the Inter-Laboratory Variation Problem: Page 4 of 4

March 6, 2020
Abstract / Synopsis: 

The problem of different cannabis laboratories obtaining different results on the same samples, inter-laboratory variation, has been studied extensively. One of the causes of the problem is different laboratories prepare their samples differently. Another issue is how varying amounts of moisture in plant material can impact potency measurements. Ideas on how to improve the situation are given.

Solutions—A Golden Analytical Method

The definition of accuracy is how far away one is from the true value (10). In cannabis analysis there are currently no standard reference materials such as a standard marijuana bud or hemp distillate. Recently I learned NIST is working on standard reference materials for hemp analysis but that might not be available for years (13). On the marijuana side there will not be standard reference materials until Federal legalization occurs. Hence, there are no agreed upon true values in this industry and accuracy is illusory. The best we can do is run the same sample over and over again and calculate a precision value.

What are we to do then? We have to figuratively put a “stake in the ground” and decide upon a standard method and instrument, and calibrate all instruments with respect to this “golden” one. For example, for potency analysis high performance liquid chromatography (HPLC) should be preferred (12), and we need to standardize on a sample preparation method, calibration method, and instrument. Once we have a “golden” HPLC and method, other chromatograph and spectrometer instruments could be calibrated to the golden one, and then used for analysis going forward (13). The advantages of spectroscopy are very little sample preparation, removing the human error associated with extensive manual sample preparation. Also, spectroscopic methods of cannabis analysis are fast and inexpensive, allowing for more representative sampling to be performed.

As I have pointed out in the past, the method of Giese, Lewis, Giese, and Smith (12) should be the method the industry adopts in terms of sample preparation, HPLC to determine cannabinoids, and gas chromatography with a flame ionization detector (GC-FID) to determine terpenes. I have witnessed this method in action at multiple third party laboratories. As part of my own work, I have correlated HPLC results to mid-infrared (IR) results on the same sample set at several laboratories using different HPLC potency methods. I always obtain the best correlation to laboratories using the method of Giese and colleagues. Assuming mid-IR is an unbiased, independent, orthogonal method, this indicates the Giese and colleagues method is the best.


The phenomenon of inter-laboratory variation is a real problem in cannabis analysis. Part of the problem is variation in sample preparation across laboratories. Variables such as grinding, moisture content, extraction solvent, varying amounts of sample and solvent, and human error contribute to the problem. The industry needs to decide on a standard sample preparation protocol and analysis method, or else the inter-laboratory variation problem will continue to plague us.

  1. B.C. Smith, Cannabis Science and Technology 2(2), 12–17 (2019).
  2. B.C. Smith, Cannabis Science and Technology 2(3), 10–14 (2019).
  3. M.O. Bonn-Miller, M.J.E. Loflin, B.F. Thomas, J.P. Marcu, T. Hyke, and R. Vandrey, JAMA, J. Am. Med. Assoc. 318, 1708 (2017).
  4. B. Young, The Seattle Times, January 5, 2016.
  5. L. Wagner, M. Bott, M. Villarreal, and M. Horn, NBC Bay Area, November 16, 2017,
  6. B.C. Smith, P. Lessard, and R. Pearson, Cannabis Science and Technology 2(1), 48–53 (2019).
  7. California Bureau of Cannabis Control Regulations, Section 5719.
  8. 115th United States Congress, Senate Bill S.2667, ”Hemp Farming Act of 2018.”
  10. B.C. Smith, Cannabis Science and Technology 1(4), 12–16 (2018).
  11. M. Giese, M. Lewis, L. Giese, and K. Smith, J. AOAC Int. 98(6), 1503–1522 (2015).
  12. B. Smith, M. Giese, and M. Lewis, unpublished results.
  13. B.C. Smith, Cannabis Science and Technology 2(6), 28–33 (2019).

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 3(2), 10–15 (2020).