The topic: 3-monochloropropanediol(3-MCPD), 2-MCPD, and glycidol in edible oils and fats, as well as in oil and fat-containing foods, can be determined using a variety of standard methods: 1. The indirect, differential method, 2. the Kuhlmann (SGS) method, 3. the Unilever method, and 4. the Zwagerman/Overman method. The methods have distinct features and vary in terms of both how labor intensive they are and the equipment required. In cooperation with major players in the food industry and associated contract laboratories, the GERSTEL application team has developed fully automated sample prep solutions for 3-MCPD, 2-MCPD and glycidol that are used internationally by key players.
Indirect or differential method: Long established and the most widely used standard method for the determination of fatty acid bound 3-MCPD, 2-MCPD, and glycidol in vegetable fats and oils by GC-MS. Fast, rugged and reliable, the method is used for inspection of incoming goods, quality control of oils and fats in oil mills, and by food producers and associated contract laboratories. The differential method is available under different names: AOCS method Cd 29c-13, DIN EN ISO 18363-1, and DGF standard method C-VI 18 (10). These have much in common: Two aliquots of an oil or fat sample are saponified and the reactions are stopped using an acidic chloride and bromide solution, respectively. The analytes are derivatized with phenylboronic acid (PBA) and the amount of 3-MCPD originally present in the sample is determined directly, while the amount of glycidol is determined indirectly by a differential measurement. The evaporation step prescribed in the AOCS method Cd 29c-13 is performed as part of the automated workflow by the GERSTEL MultiPurpose Sampler (MPS) coupled directly to the GC-MS system. While triple quadropole MS systems are most widely used, the required limits of quantitation can be achieved in most samples (except infant formula) using a single quadrupole mass spectrometer (MSD). The installed column backflush eliminates excess reagent and high-boiling residue, preventing sample to sample carry over and ensuring long-term system stability. Results show good correlation with reference data. Excellent standard deviations are obtained for the complete analysis including sample preparation workflow as proof of successful automation.
Kuhlmann (SGS) method: DIN EN ISO 18363-2:2025 or AOCS Cd 29b-13 is widely considered the gold standard among the methods for determining fatty acid bound 2-MCPD, 3-MCPD and glycidol. The method is safe and robust and reliably delivers good results. The high precision comes at a cost: More time is required along with the ability to cool samples to -22 to -25 °C. The technical implementation on a modern, integrated, fully automated analysis system is conceivable, but as yet hasn’t been requested.
Unilever method: Official designation DIN EN ISO 18363-3:2024. The difference from the difference method is mainly in the sample preparation. Only one analysis run (assay) is carried out per sample. The analytes are prepared sequentially, step by step: Glycidyl esters react with acidified sodium bromide solution to form the corresponding 3-monobromopropanediol fatty acid esters (3-MBPD), which are extracted with heptane. The extract is concentrated in the MPS evaporation station (GERSTEL mVAP) and the residue taken up in tetrahydrofuran (THF). The 3-MBPD, 2-MCPD and 3-MCPD fatty acid esters are then converted into an analyzable form by placing them in an acidic environment at 40 °C for 16 hours followed by derivatization with phenylboronic acid (PBA) in an ultrasonic bath and extraction with n-heptane. The extract is concentrated in the mVAP and the residue is taken up in a small amount of solvent and analyzed by GC-MS. The workflow is in compliance with the standard method and the automation significantly improves the laboratory process: Sample throughput is increased, the analysis turnaround time is improved, and exposure of laboratory staff to potentially toxic solvents and chemicals can be significantly reduced as well.
Zwagerman/Overman method: ISO 18363-4:2021 relies on several internal standards to compensate for even small deviations, such as, for example, influence on the glycidol analysis result at elevated 3-MCPD levels. The use of a triple quadrupole mass spectrometer (TQMS) is mandatory and analytes are determined in multiple reaction monitoring mode (MRM). The standard method and all associated sample preparation steps are performed by a GC-MS/MS system coupled to a GERSTEL MultiPurpose Sampler (MPS), the analysis is fully automated. To accurately dispense a wide range of liquid volumes, the autosampler is equipped with a 1 mL syringe for sample preparation steps and a 10 μL syringe for injection of prepared extracts. A module for efficient vortex-like shaking required for extraction, a cooled sample tray for temperature control during transesterification, and a fast wash station are also integrated. High boiling residues and excess reagent are eliminated from the analytical column using a backflush system. The method is validated and is used, for example, in the analysis of vegetable oils and animal fats. Successful participation in a round robin test confirmed the system performance with relative standard deviations below four percent for all analytes in different matrices. The limit of quantification (LOQ) of 0.1 mg/kg required by the ISO standard is reached with a significant margin of safety. A further lowering of LOQs can be achieved by adding evaporative concentration (GERSTEL mVAP) to the automated system. The GC-Triple Quadropole MS delivers exceptionally clean chromatograms with minimal interference and automation enables 24/7 around-the-clock productivity. Priority samples can be added to running sequences for maximum flexibility.
Which method to use: The indirect method, also referred to as the differential method and the Zwagerman/Overman method are the methods of choice when time is of the essence, for example for quality control (QC) or for incoming raw products at a production facility. The methods are similar, but the Zwagerman/Overman method is slightly faster than the differential method and significantly faster than the Unilever and Kuhlmann methods. The Zwagerman/Overman method uses several internal standards, increasing the cost per analysis, but delivers highly precise and accurate results. The differential method is still the preferred method in most settings given that it is well known and established. Switching to new methods is not always easy in the spirit of "never change a running system". However, the change could bring added value in terms of greater efficiency and quality of the analysis process. Whichever method is used, adding a new GC-MS system or upgrading an existing one with automated sample preparation for determination of 2-, 3-MCPD and glycidol is frequently a good investment.
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