MOSH MOAH Cutting System

The analysis of mineral oil hydrocarbons contamination in food and food contact materials is an emerging issue in the last years. There are several sources for possible contamination throughout the whole production chain from raw material to the packed good.

Due to their chemical structures mineral oils can be divided into two fractions: Mineral oil saturated hydrocarbons (MOSH) consist of linear and branched alkanes, and alkyl-substituted cyclo-alkanes, whilst mineral oil aromatic hydrocarbons (MOAH) include mainly alkyl-substituted polyaromatic hydrocarbons. The MOSH can  accumulate in the human body and cause granulomas^1,2, the MOAH which makes up 15-30% of the whole mineral oil fraction may contain potential mutagenic and carcinogenic substances^2,3. At the moment there are no legal limit in Europe for MOSH/MOAH, but MOSH concentrations up to 2 mg/kg and MOAH levels below 0,5 mg/kg are considered to be acceptable.

The analysis of MOSH and MOAH is a big challenge due to its really complex composition of unresolved and unidentified substances and the formation of irregular humps.  The method of choice uses on-line coupling of liquid chromatography with gas chromatography and flame ionisation detection (HPLC-GC-FID; see Fig.1)4,5. The information generated by this analysis method is the total amount of MOSH and MOAH.

The HPLC gives a high separation efficiency for the MOSH and the MOAH fraction using gradient elution with hexane and up to 30% dichloromethane, thereby saving resources in terms of solvent consumption and columns in comparison with other liquid chromatography sample preparation methods like solid phase extraction. On-line UV-detection enables the control of the fractionation cuts. High volume injection of 450µL into the GC done via Y-interfaces is used to gain sensitivity. The Y-piece connects a fused silica capillary (one for mosh, one for moah), which acts as transfer line for the eluent from LC, the carrier gas line and the guard column. The whole fraction is transferred to the guard column and the transfer line backflushed with the carrier gas. The GC consist of two pairs of columns, one for the MOSH and one for the MOAH fraction. The short guard columns with 0.53 mm inner diameter are essential for solvent evaporation prior further separation of the fraction on the analysis columns, which helps to identify interferences such as squalene. The advantage of using FID as detector is the “identical” response to all classes of hydrocarbons and the consequently ease of quantification. Due to the on-line coupling a closed, fully automatized system is provided, without the possibility of sample contamination during pre-separation. For control of sample preparation, fractionation and for quantification a set of nine internal standards is added. This standards act as markers for the beginning and the end of the mosh and moah fraction, as indicators for loss of volatile substances and are used for quantification. Figure 3 shows the MOSH (black trace) and MOAH (purple trace) of a spaghetti sample with a MOSH concentration of 12.7 mg/kg from C₁₆-C₃₅ and the marked regions of C₁₆-C₂₅ (blue) and C₂₅-C₃₅ (red). The internal standards are marked with symbols (black squares internal standards MOSH: C₁₁, Bicyclohexyl, C₁₃ and Cholestane eluting with the MOSH hump; purple stars internal standards MOAH: Pentylbenzene, 1 & 2-Methylnaphthalene, Tri-tert-butylbenzene and Perylene).