Seliwanoff’s Test for the Differentiation of Aldoses from Ketoses

This test is a keto hexose-specific timed colour reaction. It is therefore used for the differentiation of aldoses from ketoses. Dehydration is carried out in the presence of HCl ketohexoses to yield 4-hydroxy methyl furfural more rapidly than aldohexoses. In addition, these furfural derivatives condense to form a red coloured complex with resorcinol.

Seliwanoff test result

Reagents

Seliwanoff’s reagent:

Dissolve 34 ml of HCl in 68 ml of distilled water, add 0.15 g resorcinol

Procedure

• Add 1 mL of the test solution to about 2 mL of the Seliwanoff reagent and warm it in a boiling water bath for 1 min. 
• The presence of ketohexose indicates the appearance of a red colour (fructose).

Note:

• Aldohexoses, e.g. glucose, also react if the boiling is prolonged because the catalytic action of the acid is converted into fructose.
• Sucrose and inulin are also tested because they are hydrolysed by fructose-giving acids.