Investigating Vitamin C
Investigating Vitamin C
Background
Vitamin C is found in green vegetables, fruits, and potatoes. It is essential for a healthy diet. The chemical name for vitamin C is ascorbic acid. Ascorbic acid is a good reducing agent and therefore it is easily oxidised. Methods for the detection of vitamin C involve titrating it against a solution of an oxidising agent.
Where to start
There are several oxidising agents that can be used and a commonly used one is
2,6-dichlorophenol-indophenol or DCPIP. You need to standardise this against a known concentration of vitamin C. This means finding out how much DCPIP reacts with a known amount of vitamin C. You can check the end point colour by testing a small amount of vitamin C with the DCPIP and observe the disappearance of the blue colour. The end point is usually a pink colour that persists for about 15 seconds or longer.
Practical Techniques
You will need to find out about the technique of titration and how to make up accurate solutions.
Possible Investigations
· Investigate the reliability of this method at different concentrations and under different conditions. You may also find slightly different procedures for the DCPIP analysis – are they more accurate/easier?
· Investigate other analytical agents such as iodine and Nbromosuccinimide.
How do they compare to DCPIP?
· Investigate the stability of ascorbic acid under different conditions such as temperature, light and air/oxygen.
· Investigate the amount of vitamin C in foodstuffs and the effect of cooking them. · It has been shown that vitamin C can interfere with the blue-black colour of the starch iodine complex. The vitamin C can turn it from blue-black to colourless. Investigate the possibility of using this reaction to determine vitamin C concentration.
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· Investigate the use of sodium hydroxide as a reagent to analyse for vitamin C. It should be possible to carry out an acid /base type titration because vitamin C is an
Background
Vitamin C is found in green vegetables, fruits, and potatoes. It is essential for a healthy diet. The chemical name for vitamin C is ascorbic acid. Ascorbic acid is a good reducing agent and therefore it is easily oxidised. Methods for the detection of vitamin C involve titrating it against a solution of an oxidising agent.
Where to start
There are several oxidising agents that can be used and a commonly used one is
2,6-dichlorophenol-indophenol or DCPIP. You need to standardise this against a known concentration of vitamin C. This means finding out how much DCPIP reacts with a known amount of vitamin C. You can check the end point colour by testing a small amount of vitamin C with the DCPIP and observe the disappearance of the blue colour. The end point is usually a pink colour that persists for about 15 seconds or longer.
Practical Techniques
You will need to find out about the technique of titration and how to make up accurate solutions.
Possible Investigations
· Investigate the reliability of this method at different concentrations and under different conditions. You may also find slightly different procedures for the DCPIP analysis – are they more accurate/easier?
· Investigate other analytical agents such as iodine and Nbromosuccinimide.
How do they compare to DCPIP?
· Investigate the stability of ascorbic acid under different conditions such as temperature, light and air/oxygen.
· Investigate the amount of vitamin C in foodstuffs and the effect of cooking them. · It has been shown that vitamin C can interfere with the blue-black colour of the starch iodine complex. The vitamin C can turn it from blue-black to colourless. Investigate the possibility of using this reaction to determine vitamin C concentration.
52
· Investigate the use of sodium hydroxide as a reagent to analyse for vitamin C. It should be possible to carry out an acid /base type titration because vitamin C is an