Revision as of 10:05, 1 March 2013

Iodine number or “Iodine absorption value” expresses the percentage of iodine that is absorbed by the wax when treated with a suitable solution of iodine. It indicates the amount of unsaturated fat or wax acids, unsaturated esters, unsaturated hydrocarbons, and unsaturated alcohols inclusive of sterols and resins.[1]

Methods

Several variations of iodine value have been developed, although Hanus method, Wijs method and Hubl method are still widely used. The iodine number is determinated with a “carrier” for the iodine, in which case the solution may be iodine monochloride in glacial acetic acid (Wijs); iodine monobromide in glacial acetic acid (Hanus); or iodine-mercuric chloride in alcohol (Hubl).[1]

Hanus Method

Transfer an accurately weighed quantity of sample, as determinated from the accompanying table, into a 250 mL iodine flask, dissolve it in 10 mL of chloroform, add 25.0 mL of iodobromide TS, insert the stopper in the vessel securely, and allow it to stand for 30 minutes protected from, light, with occasional shaking. Then add, in the order named, 30 mL of potassium iodide TS and 100 mL of water, and titrate the liberated iodine with 0.1 N sodium thiosulfate VS until the blue color is discharged. Perform a blank test at the same time with the same quantities of the same reagents and in the same manner. Calculate the Iodine Value from formula:

[126.9(VB-VS)N] 10W

In which 126.9 is the atomic weight form iodine; VB and VS are the volumes, in mL, of 0.1 N sodium thiosulfate VS consumed by the blank test and the actual test, respectively; N is the exact normality of the sodium thiosulfate VS; and W is the weight, in g, of the substance taken for the test. [NOTE-If more than half of the iodobrimide TS is by the portion of the substance taken, repeat the determination, using a smaller portion of the substance under examination.] [2]