A Highly Sensitive Method for Measurement of Lipid Hydroperoxides by Iodimetry and Amperometric Endpoint.

T h i s report describes a procedure that permits accurate and specific measurement of lipid peroxides by iodimetry in the small samples available in many biological studies. Martin’s review (1) of methods for determination of organic peroxides indicates that most methods are based on reactions with various reducing substances. The most serious drawback of methods other than iodimetry can be ascribed to interfering substances in the reagents, in the solvents, and in the tissue extracts themselves. For specificity, therefore, we have chosen iodimetry, and for increased sensitivity, we have used an amperometrically determined endpoint that permits analysis of as little as loms equivalents of lipid peroxides. A study of possibly troublesome side reactions has been made. These include oxidation of iodide by atmospheric oxygen and by contaminants in tissue extracts and in reagents, addition of iodine to plasmalogens and to olefins, loss of iodine by evaporation, and oxidation of thiosulfate by substances other than iodine. This micro-iodimetric method undoubtedly has applications in the lipid field other than in analysis of peroxides; e.g., in measurement of plasmalogens, in determination of iodine numbers, in phenol titrations, and in measurements of periodate reduction. The