The Ehrlich reagent works by binding to the C2 position of two indole moieties to form a resonance stabilised carbenium ion compound.[1]
Medical testing
Ehrlich's reagent can be used to test for the presence of LSD. Upon reaction, the Ehrlich's reagent turns to purple indicating the presence of LSD.
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]
The reagent is prepared by dissolving 0.5[5]–2.0g of p–dimethylaminobenzaldehyde (DMAB) in 50mL of 95% ethanol and 50mL 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.
↑ O’Neal, Carol L; Crouch, Dennis J; Fatah, Alim A (April 2000). "Validation of twelve chemical spot tests for the detection of drugs of abuse". Forensic Science International. 109 (3): 189–201. doi:10.1016/S0379-0738(99)00235-2. PMID10725655.
↑ Sunshine, Irving (1969). Handbook of analytical toxicology. Chemical Rubber Co. p.408. p-DMAB-TS: To a cool soln of 65 ml H2S04 in 35 ml H2O, add 125 mg para-dimethylaminobenzaldehyde, dissolve, add 1-2 drops of FeCI3-TS.
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