Titration of Vitamin C

Titration of Vitamin C is defined as the process of determining Vitamin C concentration in any vitamin source.



Titration is mainly done using iodine.

Before starting the process, dissolve vitamin source in 100ml of distilled water, if it is a tablet and add about 200 ml of water. If the source is a fresh fruit, then squeeze and strain the juice through cheese cloth to remove pulp and seeds.



If the vitamin c source is a packaged fruit juice, then simply strain the juice through coffee filter or cheese cloth. If available in natural food sources, then blend 100 gm of fresh foods and add 50 ml of distilled water.



Mix it well and strain the mixture.

The concentration of Vitamin C can be determined by redox titration method with the use of iodine. When iodine is added to the solution containing Vitamin C during the titration process, ascorbic acid is oxidized to dehydroascorbic acid and the amount of iodine is converted to iodide ions.

ascorbic acid + I2 --> 2 I- + dehydroascorbic acid

As a result of this reaction, iodine is continuously reducing to iodide ion until the presence of ascorbic acid.



When the complete content of ascorbic acid gets converted to dehydroascorbic acid, the reduction of iodine to iodide ions comes to a halt and the free iodine reacts with starch indicator, resulting in the formation of blue-black starch-iodine complex. Formation of blue-black starch-iodine complex marks the end of titrating process.

The titration method is beneficial for determining the content in vitamin C pills, fresh fruits, packaged fruit juices and raw fruits and vegetables.Titration of Vitamin C can also be done using potassium iodate.



Potassium iodate is relatively stable that iodine solution, hence this method is relatively more reliable.

This method is characterized by addition of iodate ions to the solution containing Vitamin C. The addition of these ions result in an oxidation-reduction reaction and iodate ions are reduced to iodine.

2 IO3- + 10 I- + 12 H+ --> 6 I2 + 6 H2O

Iodine formed oxidizes the ascorbic acid to dehydroascorbic acid and further reduces to iodide ions.

ascorbic acid + I2 --> 2 I- + dehydroascorbic acid

After the completion of oxidation of ascorbic acid to dehydroascorbic acid, the free iodine forms the blue-black starch-iodine complex.



The last stage is similar to titration of Vitamin C with iodine.