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A research article published in F1000Research considers how we can improve routine monitoring of mineral hydrocarbons in cosmetics and medicinal products to minimize the potential health risk.

Introducing MOSH and MOAH

Mineral oils or mineral oil hydrocarbons are rather vague terms to describe some fractions obtained during crude oil refinement. They are usually comprised of a complex mixture of alkanes and cycloalkanes with typical chain lengths of about 20 carbon atoms.

As it is not currently possible to fully resolve these mixtures into individual components, the available analytical methods distinguish the products into two fractions: mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH).

I would not go so far to say that this is an “inadequate analysis” but it was just a pragmatic choice when no other approach was available.

Potential health hazard?

Mineral oil hydrocarbons are widely applied as ingredients in cosmetics and medicinal products, such as creams, but also as pure products (vaseline, petroleum jelly, white oil). If you check the ingredients lists on cosmetics products, mineral oil products may be listed as paraffinum liquidum, paraffin, cera microcristallina or petrolatum. Humans may also be exposed to the hydrocarbons through contact with recycled food packaging or packages with printing ink containing mineral oils.

The MOAH fraction of mineral oils is assumed to be a health hazard because some aromatic hydrocarbons are genotoxic carcinogens – cancer causing agents that can alter DNA, such as the polycyclic aromatic hydrocarbons with benzo[a]pyrene as an indicator compound.

The pragmatic choice

Online coupled liquid chromatography-gas chromatography with flame ionization detection (LC-GC-FID) used to detect, measure, and separate organic compounds in a given sample, is the current method of choice to analyse the presence of hydrocarbons. I would not go so far to say that this is an “inadequate analysis” but it was just a pragmatic choice when no other approach was available.

The downside is the rather unusual coupling of LC and GC, which is not available at many labs and requires special training of operators and rather long analysis times. The FID is also a relatively unspecific detector, which limits the chemical information available about the detected components. We searched for an alternative method, which should be more specific, more robust and if possible more rapid than LC-GC-FID.

NMR can measure a sample in 25 minutes, so we can measure more than 50 samples per day. This allows us to efficiently monitor large numbers of samples from the market.

A more specific and robust analysis

We selected nuclear magnetic resonance (NMR) spectroscopy as an alternative. This technique is related, in principle, to magnetic resonance imaging (MRI), which is perhaps better known for its broad use for medical diagnosis in hospitals. Both techniques are based on the phenomenon that certain atomic nuclei, such as hydrogen in our case, show specific properties inside a strong magnetic field dependent on the structure of the molecule and its functional groups.

For this reason, NMR gives better selectivity than LC-GC-FID, because physicochemical properties of the chemical structure of the compound are the underlying criterion for the chemical shifts observed in NMR. This enables us to distinguish aliphatic structures of the MOSH fraction from aromatic structures of the MOAH. Another advantage is that NMR can be used to measure a sample directly, only dilution is required, without prior chromatographic separation. NMR is also directly quantitative (the number of nuclei is proportional to the signal intensity) so that no calibration is required.

Better routine monitoring and surveillance of mineral hydrocarbons

NMR can measure a sample in 25 minutes, so we can measure more than 50 samples per day. This allows us to efficiently monitor large numbers of samples from the market. The obtained representative data will provide the basis for a risk assessment. Currently we do not know if the potential hazard of MOAH will lead to an actual consumer risk because there is a lack of exposure data and it is challenging to assess a mixture’s degree of toxicology. We hope that we will soon have enough data to provide an initial risk assessment.