Principle: – Chemical Assay of vitamin C depends on the marked reducing properties of the vitamin. Generally vit. C is determining in plant or animal extract by its reducing action on the dyestuff.
2, 6 dichloride phenol indophenols. In this method vit. C is oxidized by the co lour dye to dehydroascorbic acid. At the same time the dye is reduced to a colorless compound so that end point of the reaction can be easily determined. Rapid extraction and fit ration is desirable as excess may be introduced in plant products by oxidizes partially destroying vit. C during sampling and grinding. Oxidation is presented by use of methaphesphoric acid during extraction. A strongly acidic solution gives most accurate results. This titration should be complete with in one minute.
The dye has blue co lour in aqueous solution, pink in acidic soln and becomes colorless when completely
reduced.
Standardization by std. vitamin of Dye soln.
Conc. Of std. vitamin C solution == 0.1 mg /ml
therefore 25 ml of vitamin C == 2.5 mg
therefore 5 ml (burette reading) of dye == 2.5 mg of vitamin C
therefore 1 ml of dye solution == 0.5 mg of vitamin C
For Lemon Juice
Observation:-
Solution in burette — Dye Soln (2, 6 dichloride phenol indo phenol)
Solution in flask — 25 ml Extract of lemon juice [+ Meta Phosphoric acid]
Indicator — Self indicator.
End point — Colorless to pink (persist for 10 sec.)
Readings I ml II ml
Initial 0 0
Final 0.8 ml 0.8 ml
Difference 0.8 ml 0.8 ml
1 ml of dye Soln == 0.5 mg of vitamin C
therefore 0.8 ml of dye soln == 0.4 mg of vitamin C
therefore 25 ml of lemon juice Soln == 0.4 mg of vitamin C
therefore 100 ml of lemon juice Slon == 1.6 mg of vitamin C
therefore 10 ml of lemon juice == 1.6 mg of vitamin C
therefore 100 ml of lemon juice == 16 mg of vitamin C
therefore vitamin C content of lemon juice is 16 mg / 100 ml
Requirements:-
1) Fruit juice 2) Drum stick leaves 3) Dye solution
4) Extracting solution 5) Vitamin C solution (0.1 mg / ml)
Procedure: – Standardization of dye solution.
A) pipette out 25 ml of given vitamin C solution in a 250 ml conical flask Add 5 ml of dill H2SO4 and titrate with dye solution, until a rose pink co lour persists at least 5 sec.
Calculate vitamin C equivalent to 1 ml of dye solution.
B) Vitamin C content of given fruit juice: – Dilute 8 – 10 ml of fruit juice to 100 ml with 10% met phosphoric acid (water). Titrate 25 ml of this solution with dye solution.
Express Vitamin C content of the given juice in mg / 100 ml of juice.
C) Vitamin C content of drumstick leaves: – Weigh accurately about 2 gm of leaves grind it in a marten to give a fine paste. Add 25 ml of extracting solution [Metaphosphonic acid] and a small quantity of sand and grind again filter and extract the residue with another 25 cc of extracting agent. Filter and make up the volume to 100 ml with distilled water. Titrate 25 ml of this solution against the dye solution express the conc. Of nit. C in mg / 100 gm of leaves.
II For drum stick leaves.
Solution in burette : Dye solution.
Solution in Flask : 25 ml drum stick leaves extraction.
Indicator : Self indicator
End Point : Colorless to pink (persists for 10 sec.)
Readings I ml II ml
Initial 0 ml 0 ml
Final 0.2 ml 0.2 ml
Difference 0.2 ml 0.2 ml
Now 1 ml of dye solution = 0.5 mgs of vitamin C
therefore 25 ml of drum stick leaves = 0.2 ml of dye soln
therefore 0.2 ml of dye soln = 0.1 mg of vitamin C
therefore 25 ml of drum stick leaves extraction solution = 0.1 mg of vitamin C
therefore 100 ml of drum stick leaves extraction solution = 0.4 mg of vitamin C
therefore 2 gms of drum stick leaves = 0.4 mg of vitamin C
therefore 100 gms of drum stick leaves = 20 mg of vitamin C
therefore the vitamin C content of drumstick leaves is 20 mgs / 100 gms of leaves.
Inference
1) The vitamin C content of lemon juice is 16 mg / 100 ml
2) The vitamin C content of drum stick leaves is 20 mg / 100 gm of leaves.
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