How to measure vitamin C content:
Add a known amount of Vitamin C to 2cm cubed of DCPIP mixture, drop by drop. After each drop, slighty shake the test tube to mix the vitamin C. When the mixture has decolourised, you stop adding the vitamin C.
Add fruit juice to 2cm cubed of DCPIP mixture, drop by drop. After each drop, slighty shake the test tube to mix the fruit juice. When the mixture has decolourised, you stop adding the fruit juice.
To get the vitamin C content in the juice, you use the formula:
CONCb = (VOLa * CONCa) / VOLb
CONb = The concentration of vitamin C in the fruit juice in mg ml.
VOLa = The amount of vitamin C it took to decolourise the DCPIP in ml.
CONa = The concentration of vitamin C used in the first part of experiment in mg ml.
VOLb = The amount of fruit juice it took to decolourise the DCPIP in ml.