Peroxide value determination—Comparison of some methods

A comparison between the determination of the peroxide value by the methods of Wheeler and Sully (iodometric titration) and that of Stine, et al. (ferric thiocyanate method) was made. Some oxidized vegetable oils, H₂O₂, t-butyl hydroperoxide, cumene hydroperoxide, methyl oleate hydroperoxides, and methyl linoleate hydroperoxides were used as substrates. One-hundred percent of the methyl linoleate hydroperoxides were recovered by the Wheeler reduction, 85% by the Sully method. The Wheeler method was used to reduce the methyl linoleate hydroperoxides to the corresponding hydroxy acids. In the Sully procedure, the hydroxy acids are only intermediates which are dehydrated to octadecatrienoic acids. One equivalent methyl linoleate hydroperoxide oxidized two equivalents of I⁻ (Wheeler) and four equivalents of Fe²⁺ (Stine, et al.). By way of contrast, H₂O₂ needs only two equivalents I⁻ or Fe²⁺ for reduction. The excess consumption of reduction equivalents in the ferric thiocyanate method probably is caused by secondary reactions of the methyl linoleate hydroperoxide acyl residue.