Mineral Oil Analysis: A Slippery Problem

In food analysis, people are increasingly talking about MOAH and MOSH – but what are they, and why are they in the spotlight?

The terms mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) were first used in 2008, when our lab started to distinguish between these two fractions of mineral oil contamination by HPLC separation. In fact, we began studying them two decades before this; it was 1988 when we were using on-line LC-GC coupling to perform a different analysis entirely, but by coincidence, the mineral oil contamination showed up in the chromatograms.

In these initial experiments, we discovered that jute bags – used to transport cocoa beans, rice, hazelnuts, and more – were the source of the mineral oil contamination. The oil is used to soften the fibers in the jute bags, and during transportation or storage there is migration of the volatile parts of these mineral oils. Since then, many other potential sources, such as recycled paper and board, lubricants and the environment, have been found to contaminate our food supply with mineral oil hydrocarbons.

Why is this important? It has since been discovered that MOSH accumulate in the human body, and concern has therefore been growing about their possible adverse effects – though quite how much harm they pose to humans is still unclear. It is suspected – though has not been adequately proven yet – that the toxicity of saturated hydrocarbons is different to aromatic hydrocarbons. In the class of three and more ring polycyclic aromatic hydrocarbons, there are certainly species which are carcinogenic; for example, benzo-a-pyrene.

MOSH/MOAH are a complex mixture of thousands of isomers; they don’t produce single signals in the chromatogram, but rather “humps”. Interpreting such chromatograms can be difficult, and needs experience 
and training.

On-line LC/GC-FID is already used in routine analysis, and there are auxiliary methods that are able to remove interfering long-chain n-paraffins or olefins from natural origin. For example, epoxidation renders olefins more polar and they are therefore removed from the MOAH fraction, and long-chain n-paraffins are removed by chromatographic pre-separation on activated aluminium oxide. If there is a need for further characterization, comprehensive 2D-GC is a very powerful tool that allows further separation of the MOSH or MOAH humps. GC-MS and GC×GC-FID/MS add further tools to the search for mineral oil markers.

There are no general regulatory limits for MOAH and MOSH... yet. But there is an ongoing discussion. In Germany, for example, there is a draft regulation regarding the use of recycled paper and board for food packaging. Given the inherent challenges of MOAH and MOSH analysis, it is critical that we prepare analytical methods that are able to adequately support upcoming regulatory decisions.