Duquenois-Levine Test
Definition
A three-reagent presumptive test for cannabinoids: vanillin + acetaldehyde in ethanol (Reagent 1), concentrated hydrochloric acid (Reagent 2), and chloroform partition (Reagent 3). Cannabinoids give a purple colour in the chloroform layer; the partition step reduces false positives from polyphenolic plant materials.
- Reagents required
- Vanillin, acetaldehyde, ethanol, concentrated HCl, chloroform
- Positive result
- Purple or violet color in the chloroform layer
- Test type
- Presumptive (requires confirmatory testing)
- Detects synthetic cannabinoids
- No
Common questions
What does the Duquenois-Levine test detect?+
It is a presumptive color test for natural cannabinoids such as THC. A purple or violet color in the chloroform layer signals the likely presence of cannabis. It does not detect synthetic cannabinoids.
How does the test work?+
You add three reagents in sequence: vanillin and acetaldehyde dissolved in ethanol (Reagent 1), then concentrated hydrochloric acid (Reagent 2), then chloroform to extract the color (Reagent 3). If cannabinoids are present, they migrate into the chloroform layer as a purple or violet color.
Why use the chloroform partition step?+
The partition into chloroform reduces false positives from polyphenolic plant materials. This extra step improves specificity over simpler color tests.
Related terms
- Marquis Reagent
- A presumptive drug test reagent consisting of formaldehyde in concentrated sulphuric acid, first described by Edmund Marquis in 1896. It produces characteristic...
- 6-Monoacetylmorphine (6-MAM)
- A transient diagnostic metabolite of heroin (diacetylmorphine) formed by the rapid hydrolysis of one acetyl group. Half-life is 6 to 25 minutes...
- Δ9-THC (Tetrahydrocannabinol)
- The primary psychoactive cannabinoid in cannabis, formed by decarboxylation of THCA. Molecular formula C21H30O2, MW 314.46 g/mol. The 0.3% dry-weight threshold under...
- AMB-FUBINACA (ADB-FUBINACA)
- A third-wave synthetic cannabinoid of the fluorobenzyl indazole carboxamide scaffold identified in the 2016 New York mass-poisoning event; associated with intense, prolonged...
- Benzoylecgonine
- Major urinary metabolite of cocaine. Detected by immunoassay screen and LC-MS-MS confirmation; window of detection 2 to 4 days for occasional use.
- CBD (Cannabidiol)
- A non-psychoactive cannabinoid and regioisomer of THC with the same molecular formula but a different double bond position. Dominant in hemp varieties....
- CBGA (Cannabigerolic Acid)
- The universal biosynthetic precursor to the major cannabinoids. Formed in cannabis trichomes by condensation of geranyl pyrophosphate and olivetolic acid; converted to...
- CBN (Cannabinol)
- An oxidation product of THC that accumulates as cannabis ages. High CBN:THC ratio is a qualitative marker of old or degraded cannabis...
- Charas
- Under the NDPS Act 1985, the separated resin from cannabis including concentrated preparations and hashish; distinct from ganja (flowering tops) and from...
- Cobalt Thiocyanate
- Co(SCN)2 in aqueous solution; the active reagent in the Scott test for cocaine. Cocaine forms a lipophilic blue complex with cobalt thiocyanate...
- False Positive (Presumptive Test)
- A positive colour response from a compound that is not the targeted controlled substance. Common sources include diphenhydramine (Marquis orange, Scott blue),...
- HHC (Hexahydrocannabinol)
- A hydrogenated form of THC produced by catalytic reduction of the 9-10 double bond, existing as (9R)-HHC (active) and (9S)-HHC (less active)...
Explained in these topics
- Cannabis: THC, CBD, HHC and the Synthetic Cannabinoid WavesA three-reagent colour presumptive test for cannabis: vanillin/ethanol/HCl reagent plus concentrated HCl plus chloroform extraction produces a purple-violet co...
- Presumptive Colour Tests: Marquis, Mecke, Duquenois-Levine, Cobalt Thiocyanate and ScottA three-reagent presumptive test for cannabinoids: vanillin + acetaldehyde in ethanol (Reagent 1), concentrated hydrochloric acid (Reagent 2), and chloroform p...
- Stimulants, Narcotics and Opiates: Forensic ToxicologyVanillin and acetaldehyde in ethanol plus concentrated HCl, then chloroform partition. Violet color migrating into the chloroform layer is presumptive for cann...