Ehrlich's reagent

Ehrlich reagent can be used to detect urobilinogen, which can indicate jaundice or other liver-related issues.

A very common Ehrlich test is a simple spot test to identify possible psychoactive compounds such as tryptamines (e.g. DMT) and lysergamides (e.g. LSD). It gives a negative test-result for 25I-NBOMe and many other non-indole-related psychoactives. The reagent will also give a positive result for opium, because of the presence of tryptophan in natural opium.^[3]

Pyridoxine, present in vitamin supplements, can give positive results to the Ehrlich test, showing a pink colour change.^[4]

The reagent is prepared by dissolving 0.5^[5]–2.0 g of p–dimethylaminobenzaldehyde (DMAB) in 50 mL of 95% ethanol and 50 mL of concentrated hydrochloric acid^[6][7] and is best used when fresh. Other alcohols, such as 1-propanol, can also be used as well.^[8]

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

• The van Urk reagent, which uses 0.125 g of p-DMAB, 0.2 mL of ferric chloride solution (25 mg/mL) in 100 mL of 65% sulfuric acid.^[9][10][11] This is sometimes referred to as the Hofmann reagent or p-DMAB-TS (Test Solution) and gives slightly different colours with different indoles.
• 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 a 1:1 solution of 5% DMAB in concentrated phosphoric acid (specific gravity 1.45) to methanol.^[3][12]

• Drug checking
• Other alkaloid spot tests:
  • Froehde reagent
  • Indole test
  • Kovac's reagent, similar but uses isoamyl alcohol
  • Liebermann reagent
  • Marquis reagent