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Color Testing Suspected Marijuana Samples

Once the New Jersey state chemist has completed the first step of marijuana identification through microscopic evaluation, the next step is to perform a color test. Color tests are presumptive tests that do not conclusively prove a sample is marijuana.

Color testing, in general, involves placing chemicals into a test tube or ceramic dish with a small sample of the suspected drug. The chemist then looks for specific color changes, depending on the chemicals used. If a specific color change takes place, then the chemist should proceed to do confirmatory testing with a gas chromatograph-mass spectrometer. [See below video of Kevin Leckerman color testing in a laboratory]

The color testing that is used for marijuana testing is known as the Duquesnois-Levine Color Test (D-L). The D-L test involves placing the suspected a marijuana sample into a test tube and then adding acetaldehyde, vanillin, and hydrogen chloride to the sample. Once the chemicals are mixed with the sample, the chemist will look to see if the liquid turns to a deep purplish color.

This D-L color test has been modified since its original development to include a second step. This second step involves adding chloroform after the chemist notes the purplish color of the liquid. The addition of chloroform 2-3 minutes later causes separation of colors in the test tube. If the sample is marijuana, then a top chloroform layer of color in the liquid should be obvious. This modified version of the D-L is supposed to eliminate false positive identification of the marijuana.

Of course, problems can arise with this form of color testing. Primarily, the chemist does not take pictures of the color testing that was done. So, a defendant has to rely on the word of the chemist concerning the identification of colors. Moreover, the laboratory should have each chemist proficiency tested to determine how often the chemist is making false positive identifications of suspected marijuana. Otherwise, there is no way of determining how accurate the eyes of the chemist are for making such important identifications. All of this information should be explored through the legal discovery process in the municipal court.

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