Ehrlich's Reagent

Ehrlich's Reagent is an indicator with p-dimethylaminobenzaldehyde as its core component. Ehrlich's Reagent is mainly used for the identification of enterobacteria, non-fermentative bacteria, fastidious bacteria and anaerobic bacteria, as well as the detection of indole derivatives and amines. It turns pink, red or purple when a positive reaction occurs. Ehrlich's Reagent undergoes colorimetric reactions with urobilinogen, indican, phenol, allantoin, tryptophan and uric acid, and forms yellow-green products when reacting with sulfur derivatives ^{[1] [2]}.

In Vitro, Ehrlich's Reagent reacts with the β-position of indole molecules at a molar ratio of 1:2 in 95% EtOH with HCl as the catalyst to form β-bis (indolyl) methane^[1]. Ehrlich's Reagent produces a stable yellow color with urea present in deproteinized blood, serum, plasma, or urine filtrate after treatment with activated carbon. It shows no significant reaction when the acetone concentration reaches 500mg/100ml, and is not interfered with by ammonia^[2].

References:
[1]. Lamb AC, et al. Product in indole detection by Ehrlich's reagent. Analytical biochemistry. 2015 Sep 01;484:21-3.
[2]. YATZIDIS H, et al. AN IMPROVED METHOD FOR THE SIMPLE AND ACCURATE COLORIMETRIC DETERMINATION OF UREA WITH EHRLICH'S REAGENT. Journal of clinical pathology. 1964 Mar;17(2):163-4.