Identification of four novel compounds in citrus oils via high‐performance liquid chromatography, using post‐column luminol‐mediated chemiluminescence detection and NMR analysis

Abstract

AbstractTwo unknown peaks were sometimes observed during analysis for terpene hydroperoxides (THPs) in various citrus oils using high‐performance liquid chromatography with post‐column luminol‐mediated chemiluminescence detection (HPLC‐CL). These two peaks showed behaviour similar to previously observed peroxyhemiacetals (PHAs) that formed from THPs and aldehydes in citrus oils. Like those PHAs, the unknown peaks also diminished in aqueous solution over time, but instead of liberating THPs, H2O2 was the product of dissociation. Working in tangerine oil, a similar investigation was performed as per our previously reported work on terpene‐derived PHAs, and these two unknown peaks were attributed to PHA adducts of H2O2 with octanal (C8 ald) or decanal (C10 ald), respectively. Each peak consisted of an enantiomeric pair, and the identification of these four compounds was made via HPLC‐CL retention time matching using two separation systems with different selectivity, and NMR analysis. The two enantiomeric adducts from H2O2 and octanal co‐eluted with linalool acetate hydroperoxide (Lin‐Ac‐HP) if it was present in the oil, but they can be distinguished by re‐injecting aged prepared samples. The H2O2‐derived PHAs will slowly dissociate and therefore be decreased by the sample preparation treatment while any Lin‐Ac‐HP that may be present will remain unchanged or increase.