Determination of Total Hydroperoxides in Oxidized Vegetable Oils Based on Triphenylphosphine Oxidation Using Electron Ionization Mass Spectrometry

Abstract

A method for determining the peroxide value (POV) of oxidized vegetable oil using electron ionization mass spectrometry (EI-MS) was developed. The range of POV measured by the method developed in this study is 0-100 meq/kg, which is a matter of interest for those involved in the vegetable oil industry. This method consists of three steps: the hydroperoxides in the sample oxidize triphenylphosphine (TPP), which produces triphenylphosphine oxide (TPPO); the TPPO concentration in the reaction solution is determined by EI-MS; and the POV of the sample is obtained from the calibration curve, which correlates the POV from the iodometric method with the TPPO concentration. The oxidation reaction of TPP was obtained by mixing TPP, oxidized vegetable oil, 3,5-di-t-butyl-4-hydroxy toluene (antioxidant), and the mixed solvent of chloroform and methanol in a test tube. The test tube was tightly sealed and then stored in the dark at 60°C for 60 min. The resultant solution was poured into a test tube for the EI and ionized using an ionization energy of 20 eV. The ion strength of the TPPO dehydride molecule, by which the TPPO concentration was obtained, was determined using the maximum value of the selected ion current chromatogram peak. The calibration curve was prepared from the POV obtained from the iodometric method and the TPPO concentration obtained by this method, using a moderately oxidized vegetable oil. For samples of air-oxidized cotton seed oil, olive oil, soybean oil, and safflower oil, the POV obtained from the TPPO concentration using the calibration curve showed good agreement with that obtained by the iodometric method.