Determination of peroxide value by conventional difference and difference-derivative spectrophotometry

The spectrophotometric behavior of the system iodide-iodine-iodate-oxygen was studied, and a simple iodometric method to determine peroxide value by conventional, difference or difference-derivative spectrophotometry was developed. The procedures are carried out inside standard photometric cells containing iodide solution to which the sample is added. Absorbance or its first derivative with respect to wavelength is measured to determine iodine concentration by means of calibration curves. No special care to avoid iodide oxidation by atmospheric oxygen is necessary. The method is applicable even to lipids that give emulsions with water, such as phosphatides, and precise results are obtained even at low peroxide values. The use of a digital spectrophotometer with data processing and programming facilities allowed development of an interactive program for automatic operation, which is outlined.