Food Science
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I am doing my Extended Essay for the IB on the Vitamin C content of various fruits and vegetables, and comparing the results for raw, cooked and organic extracts. I'm trying to find many different ways to determine the Vitamin C content for my extracts, and I've found loads of good ideas on this website.
However, I've found a technique in a book for determining the ascorbic acid content of Vitamin C tablets using a direct titration with standard iodine. It says to crush one or two tablets, put into a titration flask, add 50 cm3 of water and 10 cm3 of 2M sulphuric acid. Then to titrate this using 0.1M iodine in potassium iodide solution with 1% starch solution as the indicator.
I know this would work for Vitamin C tablets, but would this work for determining the Vitamin C content of various fruits and vegetables? Would you use this process, and if not, which one do you recommend?
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Igloo writes ...
The titration of a vitamin C tablet with a solution of iodine works because the only reducing agent in the tablet is vitamin C. However, fruit and vegetable extracts tend to contain other reducing agents too, and these are often oxidised by the iodine, giving higher titration readings as a consequence.
Iodine is therefore not the best choice of reagent since it is not specific enough. DCPIP (2,6-dichlorophenolindophenol) is the normal choice since it generally targets only the vitamin C present. NBS (N-bromosuccinimide) is an alternative choice. You will find more details of each of these on our React website via FAQs and our vitamin C investigations tutorial.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 14 April 2008
