Ehrlich Test- Definition, Principle, Procedure, Result, Uses


Ehrlich test is a biochemical test that detects the presence of tryptophan, an amino acid, in a protein sample. The test is based on the reaction of tryptophan with Ehrlich reagent, which is a solution of p-dimethylamino benzaldehyde in sulfuric acid. The reaction produces a blue-violet condensation product that can be enhanced by adding sodium nitrite. The test is named after Paul Ehrlich, a German Nobel laureate who discovered this reaction while studying typhoid fever and diarrhea. Ehrlich test has various applications in medical and forensic fields, such as:

  • Diagnosing diseases that affect the liver, bile ducts, and blood cells, such as hepatic jaundice, hepatitis, hemolytic anemia, and carcinoid syndrome.
  • Identifying psychoactive substances that contain indole or benzyl pyrrole rings, such as tryptamines and ergoloids (e.g., LSD).
  • Detecting urobilinogen, a breakdown product of hemoglobin, in urine samples.

Ehrlich test is also known as p-dimethylamino benzaldehyde test or specific amino acid test. It is one of the oldest and simplest tests for tryptophan and indoles. However, it has some limitations and sources of error that need to be considered while interpreting the results.