This assignment shall suggest appropriate procedures for the determination of vitamin c in the manufactured products given. The procedures shall be useful in determining vitamin C in sample A-which contains a selection of old products (a lemon, orange, and blackcurrant drinks) and sample B-which contains a selection of new products (a lemon, orange and blackcurrant drink).The investigation allows someone to know which brand or which type of soft drink contains less, more or no vitamin C. the results are then compared and interpreted.
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The basic procedure described here can be applicable to all types of soft drinks. The process of determination of ascorbic acid involves titration which is usually done with either iodine or blue dye. This experiment will use the blue dye Dichlorophenolindophenol (DCIP) as the indicator.
The blue dye used in this experiment is the 2, 6 dichlorophenolindophenol (2, 6 DPIP).It is blue in neutral alkaline solution and red in acidic condition. Its reduced form is colorless. When titrating an acidic solution against (2, 6 DCIP) the blue reagent turns colorless at the presence of ascorbic acid. When all the acid has been consumed any excess dye turns the solution pink. (Rastogi, 2005)
- Only the ascorbic acid or vitamin C in the drink will react with the dye.
- The reduction of vitamin C will be negligible. This is because Vitamin C decomposes very fast when exposed to light and oxygen.
Pipettes (10ml). Burette, pipette filler, filter paper, volumetric flask, beaker, conical flask, filter tunnel and flat bottomed flask.
A control containing a solution of known amount of vitamin C, blue dye and a selection of old and new products (lemon, orange and blackcurrant drink)
Standardization of blue dye
- About 30.0 cm3 of standard ascorbic acid (vitamin C) is solution is pipetted into a conical flask
- The blue dye is then titrated rapidly from a burette.
- The end point is then taken to be when the dye turns colorless.
- The blue dye is diluted to about 1.00 dm3 of the solution
- About 15.0 cm3 of sample a is (lemon, juice or black currant drink) is pippetted to a conical flask an then diluted to 60.0 cm3
- The blue dye is then used as a titre.
- Titration continues until the color changes from blue to colorless
- The experiment is repeated to all the samples i.e. lemon, orange and blackcurrant.
- The procedure 1-4 repeats for sample B.
The results are recorded, compared and interpreted. The following table is used to put down data for the various samples.
This table is draw for both sample A and B
Ascorbic acid (control)
The amount of vitamin C in a solution can be worked out by finding out how much must be added to 1 cm3 of the blue dye to turn it clear. To determine the above it is important to first find out the relationship between the blue dye and the standard ascorbic acid solution. In our case we calculate as follows:-
Assume that xcm3 is the blue dye used to 30.cm3 of a solution containing about 0.1mgcm-3 of ascorbic acid
Then x cm3 of blue dye = 4/x mg of ascorbic acid which brings to the conclusion:
1 cm3 of dye=3/x mg of ascorbic acid. This equation can then be used to estimate vitamin C in fruit juice using the following formula (Rastogi, 2005).
Mg/100 ml of test solution=T/st*2*dilution.
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Where T is the titre value and St is the titre value obtained with the standard ascorbic acid solution.
Many experiments have shown that canned orange juice seems to have the highest concentration of vitamin C; fresh orange juice usually has the lowest.
Rastogi, S.C. 2005. Experimental Physiology, New Age Publishers.