Analysis of mineral oil in food: An analytical challenge

Mineral oil can enter the food chain in many different ways: (i) as a contaminant via e.g. environment or lubricants used in equipment or machinery, (ii) as an additive or technical auxiliary or (iii) as a residue via the migration from materials and objects that come into contact with foodstuffs. The analysis is very challenging since mineral oil is a very complex mixture. Among the many different substances present in mineral oil, two main types can be distinguished: the saturated hydrocarbons (MOSH) comprising a complex mixture of linear, branched and cyclic compounds and variable amounts of aromatic hydrocarbons (MOAH). Both MOSH and MOAH form “humps” of unresolved peaks in the chromatograms with the same range of volatility. Since these two fractions have a different toxicological relevance, it is important to quantify them separately.
Commonly, an online technique existing of a combination of Liquid Chromatography with Gas Chromatography (LC-GC) with Flame Ionization Detection (FID) is used for quantification of MOSH and MOAH. However, due to the limited availability and applications of this instrumentation, another technique (offline) can be implemented. The offline technique exists of separation of both fractions by Solid Phase Extraction (SPE) using silver nitrate/silica followed by evaporation and quantitative determination of both fractions by GC-FID with large-volume injection. An overview of both techniques with their advantages and disadvantages will be presented.
Besides the different techniques, the tested matrix has also an important impact, not only on data integration and interpretation but also on the sample preparation. Due to the presence of olefins and natural alkanes, some matrices require auxiliary methods such as epoxidation and clean-up with aluminum oxide.
Next, the optimized method was used to analyze a wide variety of 198 food such as dry food, vegetables, fish and meat products, sweets,…. An overview of the results of the market survey will be presented. Afterwards, the results are compared to the action thresholds as proposed by the Scientific Committee of the Federal Agency for the Safety of the Food Chain (FAVV-AFSCA, Advice 19-2017).