What is Bial's test?

Bial’s test is a chemical test for the presence of pentoses. It is named after Manfred Bial, a German physician. The components include orcinol, hydrochloric acid, and ferric chloride. A pentose, if present, will be dehydrated to form furfural which then reacts with the orcinol to generate a coloured substance

Procedure

To perform the Bial’s Test the following procedure must be followed

  • Bial’s reagent consists of 0.4 g orcinol, 200 ml of concentrated hydrochloric acid and 0.5 ml of a 10% solution of ferric chloride.
  • Saccharides are dehydrated to furfural derivatives, which develop colour with Bial’s reagent.

Indication of the presence of pentoses

The test gives us the result by the following colour changes

  •  A blue-green colour indicates pentoses or nucleotides containing pentoses.
  • A yellow-green colour indicates hexoses, and disaccharides are yellow.

Inference

Bial’s Test will distinguish between mono- and disaccharides, lactose will not react. It can be noted that Bial’s test is commonly used to distinguish between pentoses and hexoses and is, therefore, often conducted after these groups have been identified with the help of Molisch’s test (which is a test which checks for the presence of pentoses and hexoses).

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