Ehrlich's reagent

File:Para-Dimethylaminobenzaldehyde.png

p-DMAB: the active ingredient in Ehrlich's reagent

Ehrlich's reagent, also known as the "DMAB test", is a chemical test to presumptively identify indoles. It is primarily used as a simple spot test to identify possible psychoactive compounds such as tryptamines (e.g. DMT) and ergoloids (e.g. LSD). The reagent will also give a positive result for opium, despite the opiates not containing the indole functional group, because of the presence of tryptophan in natural opium. It is named after Nobel Prize winner Paul Ehrlich who used it to distinguish typhoid from simple diarrhoea.

The reagent is prepared by dissolving 0.5–2.0 g of p–dimethylaminobenzaldehyde (DMAB) in 50 mL of 95% ethanol and 50 mL of concentrated hydrochloric acid and is best used when fresh. Other alcohols, such as 1-propanol, can also be used as well.

The Ehrlich reagent is similar to a number of other indole tests:

• The van Urk reagent, which uses DMAB, sulfuric acid and an oxidant.
• The Renz and Loew reagent, which uses p-dimethylaminocinnamaldehyde and may also be used for the detection of flavonoids.
• The "improved hallucinogen reagent", which uses 5 g DMAB in 100 mL concentrated phosphoric acid (specific gravity 1.75) and 100 mL of methanol.

The Ehrlich reagent works by binding to the C2 position of two indole moieties to form a resonance stabilised carbenium ion compound.

See also

• Pill testing
• Other alkaloid spot tests:
  • Froehde reagent
  • Liebermann reagent
  • Marquis reagent