Iodine complex starch origins

Suppose 25.00 mL of an aqueous solution of iodine was titrated with 0.025 M Na2S203(aq), using starch as the indicator. The blue color of the starch-iodine complex disappeared when 28.45 mL of the thiosulfate solution had been added. What was the molar concentration of I2 in the original solution ... 

The amount of iodine complexed by starch of various origins depends on the same factors as the NMR spectra. There are satisfactory linear correlations between the iodine-binding capacity and the percentage of terminal glucose units of starch. The latter could be calculated from the intensities of the proton and carbon chemical shifts.81... 

The iodine affinity is due to the formation of colored complexes with amylose. The color of this complex depends on both the concentration of the iodine in the solution and the kind of starch. Amylose binds 20% (v/v) of iodine, to develop a blue color, whereas amylopectin binds only O.S to 1% (v/v) of iodine to give a red-violet eolor. Starch which does not contain any amylose gives a red color with iodine. Thus, evaluation of the degree of dextrinization based on the observations of Komm and Martin needs standardization of the method and approach, because ofthe variability in the origin of the starch. Table XVI shows that methods in use to date are not equivalent to one another. The color-development characteristics are again dependent on the origin of the starch. ... 

---