Undesirable mineral oil residues are found in numerous foods or food contact materials: Saturated hydrocarbons (MOSH - mineral oil saturated hydrocarbons) and aromatic hydrocarbons (MOAH - mineral oil aromatic hydrocarbons). While the first substance class accumulates in the human body, the second compound class is suspected to contain carcinogenic substances. These substances can enter food through numerous contamination pathways.
Contamination pathways for MOSH/MOAH in food
- Recycled packaging materials produced from newspapers or magazines: The use of printing inks containing mineral oil is responsible for gas phase migration into the food.
- Accidents during the transport or production of a food product.
- Mineral oil-based lubricants within the production chain.
- And many more.
In 2009, the Federal Institute for Risk Assessment in Germany (BfR) confirmed that these substances are harmful to health. In its assessment, the BfR came to the conclusion that the transition from mineral oils to food should be urgently minimized. Measurements are recommended.
Advantages of measuring with the CHRONECT Workstation MOSH/MOAH
- Halved analysis time due to 2-channel setup for simultaneous determination of MOSH and MOAH
- Removal of interferences by means of epoxidation and AlOx-Cleanup
- Options such as GCxGC-MS analysis or MOSH depletion available
- Specialized software for the evaluation of Humps
- Specially trained support team
- System setup based on over 11 years of experience with MOSH/MOAH analysis
- Continuous development in cooperation with over 185 customers
The analysis of MOSH/MOAH is performed with an online LC-GC-FID coupling. In this process, a HPLC is connected to a GC via a special interface. The GC uses FIDs as detectors, because they show a uniform response for hydrocarbons. This is the only way to quantitatively determine the sum of all individual components. Optionally, mass spectrometers can also be used for detec-tion. The aim is usually to be able to make qualitative statements about single substances.
The coupling is done via an interface, which consists of a control unit and a heated valve unit. The temperature of the valve unit can be varied from room temperature to 150 °C. The temperature control effectively prevents condensation of the HPLC solvent in the valve unit and improves the stability of the system. An integrated flushing of the valve unit with carrier gas prevents tailing of the solvent and possible carryover.
HPLC consists of a pump and a UV detector, which is used to check the HPLC chromatogram and to verify the correct fractionation. The gas chromatograph is equipped with two FIDs.
This 2-channel setup, developed by Axel Semrau, allows the simultaneous determination of MOSH and MOAH in one GC run, thus halving the analysis time.
In HPLC, the substance groups MOSH and MOAH are separated. After separation, the fractions are transferred completely to the GC. In this transfer, 450 µL of solvent per fraction are introduced into the GC and removed by evaporation via the interface before the gas chromatographic separation.
The CHRONECT Workstation MOSH/MOAH can be configured on the basis of devices by the manufacturers Agilent or Shimadzu.
The control of the entire system is done user-friendly by the software CHRONOS by Axel Semrau. Options such as automatic epoxidation or online aluminum oxide purification can be selected simply by clicking in the sample list for the respective sample.
Removal of interferences by automated epoxidation
Especially when analyzing food, interferences by interfering substances are a problem and have a negative influence on the limit of determination and accuracy of the analysis. Major interfering substances are natural olefins such as squalene or β-carotene. These elute in the MOAH fraction and can lead to false positive results for this parameter.
By reacting these components with a peracid before injection into HPLC, the olefins are converted to polar epoxides and thus separated from the less polar MOAH in HPLC. The process of epoxidation at room temperature in ethanol as solvent was developed by Marco Nestola during his work for Axel Semrau and is now part of the current standards and recommendations of the European Union. This reaction can be carried out manually in the laboratory or automated by the CHRONECT Workstation. A centrifuge integrated into the system ensures reliable phase separation after the reaction has taken place.
Removal of interference by online alumina purification
The other major interfering components are biogenic alkanes, which elute in the MOSH fraction. The DIN EN 16995 and DGF standard method C-VI 22 (20) describe the removal of these interferences by purification of the sample with aluminum oxide.
Since this manual process is very time-consuming and requires reinjection of the sample, Axel Semrau has developed an online purification using an aluminum oxide column. An additional HPLC pump is integrated into the system and the MOSH fraction is purified automatically after separation from the MOAH fraction. This online approach allows the determination of MOSH and MOAH with simultaneous epoxidation and AlOx purification in one run and has found its way into the current DGF method as an alternative to the manual approach.
Matrix-related determination limits and standards
In the analysis of MOSH and MOAH, the limit of determination depends very much on the actual matrix. This is due to interfering substances that cannot be completely removed even with epoxidation and aluminum oxide cleanup. Therefore, no general limit of quantitation can be defined for an LC-GC system. If no interferences by interfering substances occur, the CHRONECT Workstation MOSH/MOAH can be used to achieve a limit of quantification in edible oils of 2 mg/kg and sometimes lower with-out further sample purification.
There are currently two standards or meth-ods that define the analysis of MOSH and MOAH in edible oils using LC-GC-FID. The DIN EN 16995 of 2017 describes a method that allows a determination limit of 10 mg/kg. Lower limits of quantification, which are desired by many users, are possible, but sometimes require variations and cannot be guaranteed for every matrix. Due to these variations there may be deviations between the values of individual laboratories.
This problem was addressed by the DGF with the standard method C-VI 22 (20). The method described there allows determination limits of up to 1 mg/kg after sample purification, ethanolic epoxidation according to Nestola and (online) AlOx cleanup.
New: Automatic saponification and improved epoxidation
Especially for tropical vegetable fats, however, it has been shown that even sample preparation by means of the DGF standard method does not lead to satisfactory results. For this reason, the R&D department of Axel Semrau re-examined all sample preparation steps and could reduce them to the essentials, clearly with the aim of enabling complete automation. Within this process, it became apparent that epoxidation using mCPBA did not provide satisfactory MOAH quantification for tropical vegetable fats in general. Significantly better results can be achieved by using performic acid. Typical biogenic interferences can be removed more efficiently, thus, lower limits of quantification for MOAH become accessible.
Combined with automated saponification of large sample amounts and subsequent enrichment, a workflow for typical edible oils and fats could be developed that no longer requires additional manual sample preparation steps.
The CHRONECT Workstation MOSH/-MOAH can be extended by different options:
Fract & Collect
This option allows the targeted collection of a fraction for further analysis with other methods. Very often a GCxGC-MS analysis is used. This method should allow the qualitative composition of e.g. the MOAH fraction in case of positive MOAH findings to allow more precise conclusions about the origin and a more in-depth evaluation of the sample.
It allows the determination of MOAH in samples that have a very high percentage of MOSH, such as petrolatum-based cosmetics. Only the depletion of the MOSH content allows the determination of the MOAH content.
Determination of the sterol distribution
The MOSH/MOAH system can be supplemented by sterol analysis. With the CHRONECT Workstation Sterols, the sterol distribution in edible oils can be determined fully automatically.
Determination of further quality parameters
Furthermore, different quality parameters of edible oils, such as alkyl esters and stigmastadiene, can be analyzed.
Evaluation of MOSH/MOAH chromatograms
The evaluation of MOSH/MOAH analyses differs in some points from a classical gas chromatographic evaluation. First, the area of a single peak must not be determined. The entire hump of the mineral oil contamination must be quantified. Secondly, peaks on top of the hump must be subtracted depending on the type of samples, since they are considered to be not originating from the mineral oil and would thus falsify the result. For a more precise evaluation of the sample, it is also necessary to obtain partial results for certain boiling point ranges. A classical chromatography data system often has difficulties in fulfilling these requirements, so a software called Chrolibri was developed for simple, automated MOSH/MOAH evaluation.
Furthermore, the question of the origin of the contamination arises especially in the examination of consumer goods and food. The Hump Inspector builds mineral oil reference databases and uses software-based comparison of humps to determine the origin.
All CHRONECT Workstations are put into operation in advance. During a comprehensive Factory Acceptance Test not only the correct technical function but also the analytical performance is checked. After installation, this test run is repeated in a Site Acceptance Test in the customer's laboratory. In this way the analytical accuracy is verified. The system is ready for use immediately after installation.
Appropriate sample handling, prevention of blank values, use of correct chemicals and sample vessels are pitfalls that influence the result. To support the users in these important points, Axel Semrau works together with Funke Analytic Consult. This enables us to offer a training program specially adapted to MOSH/MOAH analysis.