Caramel colour and process by-products in foods and beverages: Part I – Development of a UPLC-MS/MS isotope dilution method for determination of 2-acetyl-4-(1, 2, 3, 4-tetrahydroxybutyl)imidazole (THI), 4-methylimidazole (4-MEI) and 2-methylimidazol (2-MEI). (30th July 2018)