Determination of the concentration of vitamin C in fruits/vegetables by using the DCPIP test Free essay! Download now
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Determination of the concentration of vitamin C in fruits/vegetables by using the DCPIP test
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DescriptionDetermination of the concentration of vitamin C in fruits/vegetables by using the DCPIP test
Determination of the concentration of vitamin C
in fruits/vegetables by using the DCPIP test (2008)
Principle : Vitamin C is a strong reducing agent. It can decolorize the blue dye DCPIP.
The amount of vitamin C
in a food sample
can be estimated by
the amount of it
that is used to decolorize
a fixed amount of DCPIP.
Test tube, clean and dry
Test tube rack
5 ml syringe or a good quality squeezing pipette
1 ml pipette
________% vitamin C solution, (standard for calibration) ; prepared from commercial vitamin C tablet (0.02 %)
________ % DCPIP solution, freshly prepared
Possible samples :
* grape juice, paper pack
? lemon juice, diluted from fresh squash (Citrus fruit)
orange juice, diluted from fresh squash (Citrus fruit)
orange juice, diluted from bottled drink Mr. Juicy (Citrus fruit)
* kiwi fruit juice, diluted from fresh squash (non-citrus fruit, but high in vitamin C)
? green pepper extract / juice
Use a 1 ml pipette and a pipette filler to prepare a test tube with 1 ml of blue DCPIP solution. Prepare a few in a batch.
Fill a 5 ml syringe with the standard vitamin C solution. (Or use a dropper)
Slowly (gently) add the vitamin C solution into the DCPIP test tube drop by drop. [ PRECAUTIONS : Hold the dropper vertically. Make sure that the drop size is constant.]
After adding one drop, DO NOT shake the contents.
Stop dropping when the blue colour disappears.
[The end point is taken when the blue solution suddenly becomes colourless.]
Record the number of drops of vitamin C solution required to decolourise the DCPIP solution.
Repeat the experiment twice (= two times).
Enter the results into the table below. [Each student must enter his/her data sheet.]
Repeat the experiment for other fruit juices.
Rinse the dropper/syringe with water and then a new fruit juice to reduce contamination and ensure accuracy.
Juice sample / standard vitamin C solution
The number of drops of fruit juice
required to decolorise
1 ml of DCPIP solution
Concentration of vitamin C
Calculation : [accurate to 2 decimal places.]
Since we know the number of drops of standard vitamin C solution
needed to decolourise a fixed volume of DCPIP,
by using simple proportion,
we can calculate
the amount of vitamin C
in an unknown sample
if we get comparable data.
Complete the questions in the Activity Book TWO, p.53
[Key words : reducing property ; oxidation ; heat treatment ; decolourisation ; other colour pigments ; non-citrus fruit ; sample ; inverse relation ; calibration]
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