Determination of Vitamin C in Citrus Fruits

 

The following reagents are provided in the laboratory:

ascorbic acid (vitamin C)

iodine solution

0.2   M acetic acid

fruit juices

2% starch solution

Please note: The concentration of the iodine solution provided in the laboratory is not known.  Accordingly, you will probably need to use a vitamin C solution of known concentration (an analytical standard) to calibrate your method.  Here is an example procedure for preparation and titration of a standard solution:

1.  Prepare a 1.00 mg/mL standard solution of vitamin C

2.  Use a 25.0 mL aliquot for titration

3.  Add at least 25 mL of water to the aliquot

4.  Add ~20 drops of 0.2 M acetic acid to the aliquot

5.  Add ~10 drops of 2% starch solution

6.  Titrate to the endpoint (stable bluish/black color) with iodine solution

7.  Develop a procedure for determining vitamin C in fruits, and use the procedure to gather information for the Survivor challenge question posed on the "Prelab/Introduction" section of this website.