Osazone Test or Phenylhydrazine Test

This test is used to distinguish between lactose and maltose.

The organic compound phenylhydrazine reacts to form osazones with the carbonyl carbon of sugar. The shapes and melting point, time of formation and solubility of these osazone crystals have yellow colorc haracteristics. In the following table, the characteristic of osazone are given:

Procedure

• In a test tube, take 7-8 ml of carbohydrate solution and add a pinch of phenylhydrazine to that and double the amount of sodium acetate and 10 drops of acetic acid. 
• Dissolve and allow slow cooling by shaking.
• Observe the shape of the crystal under low microscope power (10x).

Observations and conclusion

Lactose forms crystals in the form of powder puffs, maltose forms sunflower-shaped or star-shaped crystals, while glucose and fructose form identical crystals in the form of needles.