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Seliwanoff’s Test for Fructose

Seliwanoff’s test for fructose post we briefly summarises about: principle, reagents requirements, Seliwanoff’s test procedure, result, application and limitations of Seliwanoff’s test.

Seliwanoff’s Test for Fructose

Seliwanoff’s test is a compound test that distinguishes between the sugars aldose and ketose. The ketone/aldehyde usefulness of ketoses distinguishes them from aldoses.

It’s a ketose if the sugar contains a ketone group. It’s an aldose if the sugar contains an aldehyde cluster. This exam is similar to Bial’s. Seliwanoff’s test is based on the fact that ketones dry out faster than aldoses when heated.

It was called for the scientific expert who conducted the test, Theodor Seliwanoff’s. When it is put to a solution containing ketones, it immediately creates a red tint, indicating a positive test. A slower framing pink light is noticed when introduced to an element containing aldoses. To identify sucrose from fructose, we’ll use the Seliwanoff’s test.

Principle

Seliwanoff’s test is based on the idea that ketones dehydrate more quickly than Aldoses when exposed to acid. Simple sugars are produced via acid hydrolysis of polysaccharide and oligosaccharide ketoses, followed by furfural.

In a sequence of condensation events, the dehydrated ketose interacts with two equivalents of resorcinol to generate a molecule with a rich cherry red hue.

When Seliwanoff’s test reagent is applied to a solution containing ketones, a red colour appears quickly, indicating that the test is positive. Instead, when added to an Aldoses-containing solution, a slower-forming pale pink is noticed.

Requirements

Reagent

1. Seliwanoff’s reagent: add 0.05% resorcinol (m-hydroxybenzene) in 3 N HCl. Dissolve 50 mg resorcinol in 33 ml concentrated HCl and make it 100 ml with water.

Materials

1. Test tubes

2. Test tube stand

3. Pipettes

Equipment

1. Water bath

Procedure

1. To begin the Seliwanoff’s test, fill a test tube halfway with Seliwanoff’s reagent (5 mL). Make sure the amount of reagent you’re pouring into the test tube doesn’t exceed 5 ml by measuring it first.

2. Pick up the material that will be tested, measure 1 ml of it, and pour it into the test tube.

3. The solution should be heated using hot water in the third stage. Boil the solution for 5 minutes in boiling water, and then wait for the results. After some time has passed, you will see that the colour of the test tube has changed.

Results

Seliwanoff’s Test for Fructose

Positive Test: If the colour changes to red, the Seliwanoff’s Test is affirmative, indicating keto sugar (Fructose and Sucrose) is present in the solution.

Negative Test: If no red colour or a faint pink tint appears, your result is negative, indicating that Aldose sugar (Glucose) is present in the solution.

Applications

1. The method for the colorimetric determination of fructose in fermentation media employs Seliwanoff’s colour reaction.

2. The concentration of ketoses in a particular sample can be determined using a modified version of Seliwanoff’s test.

Limitations

1. A high concentration of glucose or another sugar may interfere with Seliwanoff’s test reagent by creating similar coloured molecules.

2. Long-term boiling can convert glucose to fructose by the catalytic action of acid, resulting in the formation of cherry red-complex and a false-positive result.

3. This is a broad test that does not distinguish between various ketoses; a second test is required to identify the specific ketose sugar.

Further Readings

Reference