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Hello, I am investigating how the storage method of kale will affect its vitamin C content. For example, storage in a fridge verses an incubator at room temperature and in different containers, i.e. those alone and completely air tight. However I am struggling to find a suitable control. Would the blank titration with phosphoric acid be adequate or do I need to do more? My teacher suggested doing a survey and using the most popular method of storage as my control. What do you think? Also I initially thought I would titrate with iodine but after looking at your website I am wondering if DCPIP would be better.
Igloo writes
Using phosphoric acid as your control is a perfectly adequate method, assuming that this acid is also being used during the extraction process.
Your methods of storage, at cold and “normal” temperatures, and in the presence and absence of air seem suitable enough. If you have time you could possibly investigate the effect of humidity too, via the use of a desiccator.
The advantage of DCPIP over iodine is that it specifically oxidises vitamin C, whereas iodine - a stronger oxidising agent - may oxidise other reducing material in the kale as well. However, the iodine titration has a sharper end-point, especially when it is used in conjunction with starch – so it is really a matter of weighing up the pros and cons. Perhaps you should use both titration methods to impress!
Always carry out a risk assessment and check with your teacher before starting any practical work.
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 October 2007
