Fractionation using HPLC-GC-FID

The mineral oil hydrocarbons are extracted from the matrix and separated into the MOSH and MOAH fractions, respectively, using online coupled HPLC-GC-FID. The occurrence of MOAH is always associated with a corresponding MOSH fraction. The typical ratio of MOSH to MOAH in recycled cardboard and batching oils is approx. 5:1, but can vary considerably in foodstuffs. However, a higher MOAH than MOSH content does not occur in practice.

Chromatogram interpretation

In MOSH/MOAH analysis, the hydrocarbons occur as so-called substance humps. A hump can consist of significantly more than 100,000 individual substances with similar properties (e.g. boiling point, toxicology). This is the reason for the sum quantification via HPLC-GC-FID.

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For a professional interpretation of MOSH/MOAH analyses, the chromatogram must be evaluated by experienced specialists. The example shows the MOSH hump of a food sample. Individual peaks are not taken into account in the hump integration. For better interpretation, the total hydrocarbon hump is divided into sub-sections referring to specific carbon numbers, which are dependent on the elution of n-alkanes (in the example provided, MOSH between n-C20 and n-C40). Of course, we always include the sample chromatograms in our test reports!

Sample preparation: Epoxidation

Each sample is special and requires a professional assessment with regard to any auxiliary preparation steps that may be necessary to enable the correct determination of MOSH or MOAH without false-positive results. For example, biogenic interfering substances such as terpenes often occur in plant-based foods, which can be effectively minimised by epoxidation [5], as shown in the examplary chromatogram. We are continuously improving our analytical methods based on the latest scientific findings in order to achieve the best possible analytical results.

Sample preparation: Aluminium oxide clean-up

The MOSH fraction can also be influenced by biogenic interfering substances. Frequently occurring biogenic n-alkanes can co-elute with the mineral oil hydrocarbons and potentially cause their overestimation. Using online purification on aluminium oxide (Alox clean-up), we can reliably remove the biogenic interfering substances in the MOSH fraction, as shown in the example of a sunflower oil.

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Of course, in our test report we provide a clear and precise description of the purification process we have used for your sample so that our results are comprehensible and comparable!