What is Duquenois test (Duquenois-Levine test) – in forensic science

A presumptive test for marijuana and hashish. Also called the Duquenois-Levine test or the modified Duquenois-Levine test, it consists of three reagents that react with the active substance in marijuana, THC. The reagents are a 2 percent solution of vanillin and 1 percent acetaldehyde in ethanol, concentrated hydrochloric acid (HC1), and chloroform. Dried plant matter, seeds or seed extracts, or other material to be tested is placed in a test tube and the reagents added in order. The sample is shaken and a positive result is indicated by a purple color in the lower chloroform layer. This is not a definitive test for marijuana, as there are other oily plant extracts that will yield false positive results. However, the Duquenois-Levine test is an integral part of marijuana analysis. A sequence of photos showing the test is found in the color insert.