Fruit juices which contain vitamin C usually have the amount present printed on the carton or bottle. DCPIP is used in this practical to measure the amount of vitamin C present in a range of juices.
Equipment typically required (per set):
Firstly students need to add a small amount of the vitamin C solution to a test tube (2cm3) This should then be placed in a test tube rack.
The DCPIP solution is added to the vitamin C solution a drop at a time using a burette. After each drop, the solution should be agitated slightly to mix the two. As soon as the colour of the last drop remains in the test tube, (ie the DCPIP colour does not disappear) then stop and record how many drops it took for the decolourisation to cease.
This should be repeated several times to get an average calculation of drops required. You should now know how many drops are required for a 1% Vitamin C solution. You can use this value to work out how much vitamin C there is in the juice samples.
Do the same with each fruit juice sample. You may need to dilute some of the juices for this to work correctly because the natural colour of some may make if difficult to judge when the DCPIP colour remains. Also if any the juices are highly acidic, this may also affect the outcome of this practical.
For each juice sample, work out how many drops of DCPIP it takes until decolourisation stops. You should then be able to calculate, using the value obtained from the 1% sample, how much vitamin C is in each juice.
This amount can be checked against the level printed on the carton.
Technicians will need to make up the solutions required in this practical. Refer to CLEAPSS recipe cards or SSERC (in Scotland) documentation for details on how to do this.