Is mineral oil contamination really mineral oil? Detailed elucidation by using comprehensive two dimensional gas chromatography with dual detection

Mineral oil is a quite widespread contaminant of foods. It derives from different sources, but more recently attention has been focused mainly on paperboard packaging. Such a contamination derives from the offset printing inks applied directly to the packaging, and/or from the ink present in the recycled fibers used (generally deriving from newspapers). Mineral oil contains proportions of mineral oil saturated hydrocarbons (MOSH, including n-alkanes, isoalkanes and cycloalkanes), and mineral oil aromatic hydrocarbons (MOAH), which both are characterized by humps of unresolved complex mixtures (UCM) after gas chromatographic (GC) analysis. Resolution can be greatly improved using a comprehensive multidimensional GC (GC×GC) approach, which allows to define a more detailed profile of the compound distribution in the unresolved hump, especially for the MOAH fraction, where compounds can be separated according to the number of rings. Despite the lack of structural information (obtainable using a mass spectrometer – MS - detector), the flame ionization detector (FID) is the detector of choice to reliably quantify such humps, because FIDs provide virtually the same response per unit of mass of hydrocarbons, on the contrary of the MS detector. Moreover the lack of a proper calibration standard is a serious quantification problem in MS analysis. The aim of the present work is to develop a method to simultaneously quantify and confirm mineral oil contamination, by using GC×GC with dual detection: FID for quantification purposes, and MS for confirmation. The MOSH and MOAH fraction were separated by using an SPE cartridge, manually packed with silvered silica gel (Ag-SPE), before injection in the GC×GC system. The presence of interfering compounds, in the fraction of interest, can be determined both by the position in the bidimensional plot and the mass spectrum profile acquired simultaneously. The quantitative results (both for the MOSH and the MOAH fractions) obtained were compared with those derived by performing large volume injection (LVI) GC–FID, after the same Ag-SPE fractionation step, and through a hyphenated liquid-gas chromatographic system (LC–GC).