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.
System configuration
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 mCPBA 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 current ISO standard 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 ISO 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 permits robust
de-termination limits of up to 1 mg/kg after sample purification,
ethanolic epoxidation according to Nestola and (online) AlOx cleanup and
thus represents the current state of the art in MOSH/MOAH analysis.
Further options
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.
MOSH depletion
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.
Commissioning
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.
Trainings
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.