Determination of the concentration of vitamin C
in fruits/vegetables by using the DCPIP test (2010)
Principle : Vitamin C is a strong reducing agent. It can decolorize the blue dye
The amount of vitamin C
in a food sample
can be estimated by
the amount of it
that is used to decolourize
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 (depending on supply)
● 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
● Choi sum (vegetable squash extract)
Procedure COPY these sentences onto your SBA workbook. In the future, you will
need to write experimental procedure by yourself.
1. 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 (一批） ．
2. Fill a 5 ml syringe with the standard vitamin C solution. (Or use a dropper)
3. 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.]
4. After adding one drop, DO NOT shake the contents.
5. Stop dropping when the blue colour disappears.
[The end point is taken when the blue solution suddenly becomes colourless.]
6. Record the number of drops of vitamin C solution required to decolourise the
7. Repeat the experiment twice (= two times).
8. Enter the results into the table below. [Each student must enter his/her data sheet.]
9. Repeat the experiment for other fruit juices.
10. Rinse the dropper / syringe with water and then a new fruit juice to reduce
contamination and ensure accuracy.
The number of drops of fruit juice
sample / required to decolourise
1 ml of DCPIP solution
of vitamin C
solution Trial one Trial two Trial three AVERAGE
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.
Concentration of Average number of drops of standard
vitamin C in a fruit vitamin C solution x ______ %
Number of drops of fruit juice sample
Complete the questions in the SBA workbook and worksheet p.33 (of this
[Related key words : reducing property ; oxidation ; heat treatment ;
decolourisation ; other colour pigments ; non-citrus fruit ; sample ; inverse
relation ; calibration]