Gerhardt's Test for Acetoacetic Acid and Salicylates

Gerhardt's Test for Acetoacetic Acid and Salicylates –Gerhardt's test is specific for the detection of large amounts of acetoacetic acid. It also detects salicylates in urine.

Principle :Ferric chloride reacts with acetoacetic acid and salicylates to form the characteristic colours. Reagents ---10% ferric chloride

Procedure 1. Add 5ml ferric chloride drop by drop to 5 ml of urine in a test tube.

2. A red-brown colour is formed by acetoacetic acid or salicylates.

3. In the presence of large amount of phosphates, ferric phosphates precipitates are produced.

4. To confirm the presence of salicylates or acetoacetic acid, divide the test solution in half and boil one part for 5 minutes. If the colour disappears, then acetoacetic acid is present. 

If the colour persists, salicylates are present. The acetoacetic acid on boiling loses carbon dioxide and is converted to acetone. Acetone does not react with ferric chloride.

CH₃co.ch₂cooh------à ch₃ . co.ch₃+co₂