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
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