Purification of mineral oil aromatic hydrocarbons and separation based on the number of aromatic rings using a liquid chromatography silica column. An alternative to epoxidation

The analysis of mineral oil aromatic hydrocarbons (MOAH) in vegetable oils is currently associated with high uncertainty due to various factors ranging from sample preparation to data interpretation. One significant factor is the coelution of biogenic compounds of terpenic origin with the MOAH fraction during chromatographic analysis. The common purification method is epoxidation, a chemical reaction that changes the polarity of the interferences, allowing their separation from MOAH. However, this reaction is non-selective and can lead to losses of both MOAH and internal standards. This variation is especially noticeable when using epoxidation procedures with higher reaction kinetics, such as those employing performic acid. MOAH losses also vary depending on their composition, which is unpredictable. Furthermore, 2-methylnaphthalene (2MN) and 1,3,5-tri‑tert-butylbenzene (TBB), which are the common quantification standards, are lost at different rates. As a consequence, the final MOAH quantity will vary both depending on the standard used, and on its initial composition. This work presents a new purification approach based on liquid chromatography fractionation on silica using the same column and eluents as for the usual MOSH/MOAH fractionation. This approach efficiently removes squalene, carotenes, and derivatives, without inducing inconsistent losses between the internal standards and MOAH as epoxidation does. On average, MOAH recovery using this new method was 94% (± 8%) in coconut, palm, sunflower, and olive oil, using different MOAH sources and concentrations. Additionally, perspectives are presented regarding the separate analysis and quantification of mono-/diaromatic MOAH and other polyaromatic MOAH. This is of particular interest as these two sub-fractions are associated with different toxicological properties.