Spectrophotometric determination of lipohydroperoxides and organic hydroperoxides by use of the triiodide–hexadecylpyridinium chloride micellar system

Abstract

The association complex formed between triiodide ion and hexadecylpyridinium chloride (cetylpyridinium chloride; CPC) was used to develop a spectrophotometric method for the determination of hydroperoxides, based on the ability of hydroperoxides to oxidize iodide ion to iodine in an acetic acid medium. The triiodide ion thereby produced associates with CPC cationic micelles, which results in maximum absorption at 500 nm, in addition to substantially increased absorptivity and stability constant for the triiodide complex. The micellar medium allows the determination of various hydroperoxides (hydrogen peroxide, cumene hydroperoxide and tert-butyl hydroperoxide) at concentrations between 5 × 10–7 and 2.5 × 10–6 mol l–1, with a molar absorptivity for triiodide ion of (6.51 ± 0.08)× 103 m2 mol–1(i.e., about three times higher than those typical of methods implemented in aqueous media). The proposed method was successfully applied to the determination of lipohydroperoxides in five commercially available oil samples (olive, sunflower seed, corn, cod liver and linseed) and of various organic hydroperoxides in commercial samples (the recovery of hydroperoxides from heptane ranged between 98 and 106%). The results obtained in the determination of lipohydroperoxides are consistent with those provided by iodimetric titration.