How is sodium thiosulfate used to measure iodine in a titration?

In analytical chemistry, sodium thiosulfate is used to determine the amount of iodine in a sample through a process known as iodometry. This volumetric titration relies on the quantitative oxidation of the thiosulfate ion by iodine to form tetrathionate, according to the following reaction:12

$$2S_2{O}_3^{2-}+I_2\to S_4{O}_6^{2-}+2I^{-}$$

To accurately identify the end point of this reaction, a fresh starch solution is added as an indicator. Iodine forms a distinct blue complex with starch, and the consumption of iodine during the titration is signaled by the disappearance of this blue color, indicating that all the iodine has reacted with the sodium thiosulfate. This method is widely applied not only for measuring free iodine but also for determining many other oxidizing substances that can liberate iodine from potassium iodide.321