Selivanoff's Test Performance
PURPOSE OF THE TEST:
This test is used to differentiate between ketose and aldose sugar. This test will be positive for only ketose sugar like fructose and inulin.
REAGENTS & GLASSWARES:
1. Resorcinol
2. Concentrated Hydrochloric acid
3. Selivanoff’s reagent is prepared by dissolving 0.05 g of resorcinol in 50 mL of distilled water and the 33 mL of 36% HCl in it slowly. Then add distilled water to make the final volume up to 100 mL. In this the way, the concentration of the acid become 12%.
Volume of acid x concentration of acid 33mL100mL x 36 = 12% HCl final conc.
Volume of solution
4. Test tubes, test tube stands, test tube holder, pipette with sucker, beakers and graduated cylinder.
PROCEDURE:
1) Take two neat test tubes and label them T (test sample) and C (control).
2) Add 3 mL of Selivanoff’s reagent in test tube T and test tube C with the help of pipette.
3) Add 1mL of sugar solution in test tube T and added 1mL distilled water in test tube C.
4) Mix and Boil it for in water bath for 30 seconds only and then cool it. Note the appearance of color.
INTERPRETATION:
The presence of fructose or ketonic sugar will be indicated by cherry red or pink color within 30 seconds of boiling.
This test positive for test tube T containing ketonic sugar and test is negative for test tube C containing distilled water in place of sugar solution.
PRINCIPLE:
The ketonic carbohydrates are converted into 5-hydroxymethyl furfural ring by conc. HCl which is present in the Selivanoff’s reagent. This 5-hydroxymethyl furfural ring condenses with resorcinol to make a cherry red /purple color complex.
Fructose + HCl 5-hydroxymethyl furfural ring + Levulinic acid
5-hydroxymethyl furfural ring + Resorcinol Cherry red Color complex
PRECAUTIONS:
• The final concentration of acid do not exceeded to more than 12%. Because, concentrated acid may convert aldohexoses to ketohexoses which may give false positive results.
• Heating for long period of will cause the conversion of aldohexoses into ketohexoses which can give false positive results.