Seliwanoff’s test is used to distinguish aldoses from ketoses. On treatment with a concentrated Acid, ketoses are dehydrated more rapidly to give furfural derivatives and on condensation with resorcinol give cherry red complex. The test will be answered by fructose, sucrose and other keto containing carbohydrates. If the reaction is allowed for a longer time (more than 10minutes), aldoses also may produce positive results. Seliwanoff’s test is often considered to be a test for ketohexoses in carbohydrates.
It can be noted that Sugars having free aldehyde or keto functional groups can oxidize Tollen’s, Benedict’s and Fehling’s Solutions. The product of oxidation can be used to identify carbohydrates.