Description
Ehrlich Test
The Ehrlich test is a biochemical assay used for the detection of the amino acid tryptophan and indole-containing compounds in various samples. This test is also known as the p-Dimethylaminobenzaldehyde (p-DMAB) test, derived from the main reagent used in the Ehrlich reagent.
This test is named after Paul Ehrlich, the Nobel Prize laureate, who originally developed it to differentiate typhoid fever from simple diarrhea.
Applications of the Ehrlich Reagent Kit
The Ehrlich test is considered a specific assay for detecting indole-containing compounds and has applications in various laboratory fields, including:
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Detection of tryptophan in protein samples
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Differentiation of typhoid fever from non-infectious diarrhea
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Detection of urobilinogen in urine
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Assistance in diagnosing liver diseases
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Evaluation of Carcinoid syndrome
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Identification of hemolytic processes
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Detection of biliary tract obstruction
Rapid Ehrlich Test (Spot Test)
One common form of the Ehrlich test is the spot test, which is used for detecting certain psychoactive compounds, including:
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Tryptamines
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Ergoloids such as LSD
It should be noted that natural opium shows a positive Ehrlich test due to the presence of tryptophan-containing compounds.
The Ehrlich reagent is also used for detecting the following compounds:
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Indole
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Urobilinogen present in urine
Objectives of the Ehrlich Test
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Detection of tryptophan in the sample
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Differentiation of typhoid fever from diarrhea
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Detection of urobilinogen in urine
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Identification of indole-containing compounds
Principle (Mechanism) of the Ehrlich Test
The Ehrlich reagent consists of p-Dimethylaminobenzaldehyde (p-DMAB). The reaction is based on electrophilic substitution under acidic conditions.
In this process:
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The reagent reacts with the indole ring present in tryptophan or its derivatives (such as benzylpyrrole)
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As a result, a purple–blue condensation product is formed
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Addition of sodium nitrite (NaNO₂) leads to intensification of the reaction color
