With hemp being legal, there is an urgent need to readdress the way that law enforcement identifies marijuana. The tests that crime labs currently perform based on the Thorton-Nakumura protocol need to be examined and possibly updated. The protocol consists of three different tests. Here let’s look at the second test, modified Duquenois-Levine testing.
What is the test?
This is a color test. A small sample of the sample is placed in a test tube. A reagent is added to perform the test. The reagent is made from vanillin, acetaldehyde, and ethanol mixed in a specific ratio.
How is it done?
The sample is placed in the testing vessel. Then about ten drops of the Duquenios reagent is added. The tube gets closed and then shaken for an unspecified amount of time. Then it’s opened back up, and about 20 drops of hydrochloric acid are added. The tube gets closed and shaken again. Finally, chloroform is added for the final step.
Once that has been agitated one more time the test is complete. The technician writes down any color change at every stage of the test. A positive test is one where there is a color change and a separation into two layers. The color they’re looking for is violet or purple.
Who is performing the test?
This is performed by a lab technician. They are trained in the mechanical steps of the process and given details on how to analyze it. The exact color change and layer formation that occurs is a subjective reference for the test. There are no absolute verifiable determining factors. What is happening with the test or what changes occur during the test are not addressed. The technician’s training does not cover things like cross-reactivity, false positives, or other errors.
How accurate is the test?
This is a test that could be verifiable by simply taking a picture of the test result. However, in almost all crime labs, this is not the practice. The test is performed one time, by one person, and a peer does not verify the result.
Techs are taught that a color change can diagnose the presence of THC. However, this is not the case. Many plants will give a purple color change. Plants like coffee, wood sage, ginger, sandalwood, nutmeg, and licorice all produced the color change. The United Nations found similar results when evaluating the test.