In aqueous solutions of the amylose-iodine complex the concentration of free iodine [Illv after reaching equilibrium (or closely approximating it) is determined by the following factors: temperature, pH, concentration of iodide ions and amylose, and f% of amylose. In the present paper the role of temperature, amylose concentration, and BP has been investigated. At half-saturation of amylose by iodine, the reciprocal value of free iodine defines the equilibrium constant: The relation between [I,]. in normality and temperature is the following: 5 + log [If]. = -(2.132/T) + 8.52, for BP, = 1290, 0.4 mg. amylose in 100 ml. 0.1N HCl. The value of the energy of activation E. between 2 and 52OC. is 9.72 kcal./mole. The influence of amylose concentration [Am] on photometrically determined [If]. at 20°C. in the range of 0.1-1.2 mg./100 ml. O.1N HCI f o r m , = 1290 is: 5 + log [If]. = 0.209 -0.047 log [Am]. At [Am] = 0.6 mg. amylosel 100 ml. 0.1N HCI and 20°C. the value of [I,]v depends on m, as follows: 5 + log [If]v 0.085 = + 0.222 log (lO*/m,). These above equations are summarized by the relation : l/[If]v = K . [If], = exp (16.86.5 -( E a / R T ) ] [Am]0°47(104/~,)0 222 X
Considering that the determination of [I,] by automatic photometric titration can be performed quickly and with appropriate reproducibility, this method is convenient for a rapid empirical and approximate determination of of amylose on a microscale. The iodine-binding capacity (IBC) as well as the value of Xms, have been also investigated as functions of m, by photometric and by amperometric titration.