The Marquis reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of formaldehyde and concentrated sulfuric acid, which is dripped onto the substance being tested. Different compounds produce different colour reactions. Also some times methanol is added to slow down the reaction process to observe the change in colour better. Methanol does this by slowing down the polymerisation process. It is the primary presumptive test used in Ecstasy testing kits. It can also be used to test for such substances as cocaine, opiates (e.g. methadone, heroin), and phenethylamines (e.g. methamphetamine, amphetamine). The test is performed by scraping off a small amount of the substance and adding a drop of the reagent (which is initially clear). The results are analyzed by viewing the color of the resulting mixture, and by the time taken for the change in color to become apparent:
| Substance | Color | Time (s) | Notes |
|---|---|---|---|
| MDMA or MDA | purple to black | 0-5 | may have dark purple tint |
| Amphetamine or Methamphetamine | orange to brown | 0-5 | may have a brown tint |
| 2C-B | orange to green | 5-10 | color may change from initial result |
| DXM | gray to black | 15-30 | initially no change; takes much longer to reach black than MDMA |
