Normal-phase HPLC as a superior alternative to epoxidation for biogenic interferences removal in mineral oil aromatic hydrocarbon analysis in food

The analysis of mineral oil saturated and aromatic hydrocarbons (MOSH and MOAH) contamination in food is most commonly performed using on-line coupled liquid chromatography-gas chromatography with flame ionization detection (LC-GC-FID) after several sample preparation steps. A major challenge in the analysis of MOAH is the coelution of interfering compounds, deriving from the food matrix, with MOAH, making their determination difficult. These interferences (primarily olefinic compounds) are generally removed through a chemical reaction (epoxidation), which unfortunately also leads to the partial loss of MOAH. In the present work, the purification power of normal-phase HPLC (silica phase) was investigated as a potential alternative to epoxidation, using the same LC system (column and eluents) as conventionally used for MOSH/MOAH. It was demonstrated that the method effectively removes carotenes, squalene, and some of their derivatives, which are notably abundant in palm and olive oils, while strongly reducing MOAH losses. The recovery of MOAH using this method in fact averaged 94% (± 8%) across various vegetable oils, including coconut, palm, sunflower, and olive oils, and was consistent across different MOAH sources and concentrations. Furthermore, in parallel of the demonstrated purification capabilities of the silica phase, an additional advantage of it is its ability to separate MOAH by the number of aromatic rings, allowing for the separate collection of mono-/diaromatic MOAH (1-2 rings) and those with ≥3 aromatic rings, then quantification using either GC or GC×GC. This differentiation is of importance, given the distinct toxicological properties associated with these sub-fractions.