Epoxidation for the analysis of the mineral oil aromatic hydrocarbons in food. An update
On-line coupled high performance liquid chromatography-gas chromatography-flame ionization detection (HPLC-GC-FID) used for determining mineral oil aromatic hydrocarbons (MOAH) in foods, particularly in certain oils and fats, may be disturbed by interfering olefins present as natural food components or resulting from raffination of the oils and fats. While some interference can be coped with by disregarding their peaks, others overload GC to the extent of obscuring the MOAH or form humps which need to be distinguished from the hump formed by the MOAH. In the latter cases, it is necessary to remove these interferences prior to HPLC-GC analysis. So far, epoxidation of the olefins to increase their retention time beyond that of the MOAH in HPLC is the best method available, though imperfect by causing some loss of MOAH and sometimes incomplete removal of the interference. Two methods are re-evaluated; preference is given to a slightly modified version of that proposed by Nestola and Schmidt. The performances are comparable: the losses of MOAH are similar and with both methods not all interfering olefins may be removed from refined edible oils. However, the Nestola/Schmidt method has practical advantages, the main ones being that no cooling is necessary and no solvent needs to be evaporated, which facilitates automation. Potential residual interferences must be recognized and subtracted, which can be by the characteristics of the hump they form in HPLC-GC-FID, by GCxGC-FID or by GCxGC-MS using characteristic mass fragments.