How do you test vitamin C?

im doing a science fair project "Does orange juice have as much as vitamin C as the label says? my teacher said theres a way to do that but i dont know how can someone tell me please..

How do you test vitamin C?
Two different procedures are commonly used.


1) Determination using a fluorimetry. Vit. C or ascorbic acid is reacted with o-phenylene diamine and the resulting fluorescent compound is analysed using fluorimeter.


2) An easier method is by titration, especially for liquids like OJ. Take a 10g sample into a 300mL Erlenmeyer flask, add 100mL water. Use iodine 0.1N (buy from a chemical company like Caledon or Fisher). Make a 1% starch solution by adding 1.0g of starch into a beaker then adding 100ml water, stir for 10 minutes.


Add 1-2 mL of starch solution to 300mL Erlenmeyer flask containing juice, then titrate using a burette, with a freshly shaken 0.1N iodine solution. Make sure to stir while titrating (or use a stir bar), stop titrating when colour changes to dark blue, note the colour change has to be stable for about 30 seconds.


Quantiation:


1mL of 0.1N iodine corresponds to 8.806mg of ascorbic acid (AA). Assume it took 0.2mL to complete the titration, then 8.806x0.2=1.7612 mg of AA present. Assume also the sample weighed 10.152g, then the concentration of AA in 100ml of juice is 1.7612x10.152 or 18mg AA per 100mL.