Identification of Recycled Cooking Oil and Edible Oils by Iodine Determination and Carbon Isotopic Analysis

Elemental iodine determination by ICP-MS and carbon isotope analysis by EA-IRMS were jointly employed to identify recycled cooking oil from edible oils. Iodine in 204 oils demonstrated that recycled cooking oils can be distinguished from soybean oil, maize oil, colza oil, peanut oil, sunflower oil and olive oil with the exception of tea oil and mixed oil. These two types of oils can be definitively distinguished from recycled cooking oil in the carbon isotope ratio analysis. It was proposed to use total iodine analysis as the primary screening method and the carbon isotope ratio measurement as a secondary method for confirmation and verification. For routine screening, threshold values of Iodine determination and δ 13 C measurement were determined to be 20 ng g −1 iodine and a range of −27.3 to −28.5 of δ 13 C, respectively.