ASTM D5554 Determination of Iodine Value of Fats and Oils
Oxidation of oils may produce acid, sludge and varnish. Oils that contain a large number of double bonds (highly unsaturated oils) may be more prone to oxidation than oils with few double bonds. The iodine number provides an indication of the number of double bonds – low iodine numbers indicate a small number of double bonds, large iodine numbers indicate large numbers of double bonds. It has also been found that the Iodine Value may be used to predict the compatibility of oils to elastomers because the degree of saturation of the molecule indicates its tendency to de-polymerize the rubber structure. This test determines the iodine number using a titration with a visible blue endpoint.
A specified weight of sample is placed in a flask, iodine mono-chloride reagent is added and the mixture is given time to react. Potassium iodide and water are then added. Using a starch indicator, the mixture is titrated with sodium thio-sulfate until a blue color is obtained. The value of the blank is subtracted and the iodine number is reported.