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|
Dissolve 34 ml of HCl in 68 ml of distilled water, add 0.15 g resorcinol
- 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).
- 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.