In addition, duplicate analysis of each sample prepared in two different ways is needed in order to differentiate between 2-MCPD, 3-MCPD and glycidol.
Gerstel experts have developed a fully automated sample prepara- tion solution, integrated with the GC/MS system that replicates the AOCS Cd 29c-13/ DGF C-VI 18 (10) methods step by step on a robotic sampler. “The automated sample preparation is performed on a Multi Purpose Sampler (MPS robotic Pro) Dual Head version with two independently moving towers fitted with different syringe sizes. This means that larger amounts of liquid can be handled for sample preparation with one syringe while another smaller syringe handles smaller volumes, for example, used for injection into the GC/MS,” says Dominik Lucas, formerly Application Specialist, now member of the German sales organization within Gerstel. In addition, method steps such as liquid-liquid extraction, solvent evaporation, solvent exchange to a GC-compatible solvent and analyte derivatization, are fully automated and very efficiently integrated in the overall method. Finally, the MPS introduces the prepared sample to the GC/MS system. The required steps of the implementation of DGF C-VI 18 (10) are as follows.
Manual preparation (two steps):
- Weigh a 100 mg sample in a vial
- fill a second vial with sodium sulfate as drying agent (drying vial)
This is followed by the automated preparation with the Gerstel MPS:
- Add MTBE to the sample,
- add ISTD solution and mix,
- add MeOH/NaOH solution,
- shake and incubate,
- add NaCl solution (Sample Preparation A) or NaBr solution (Sample preparation B),
- add n-hexane,
- shake and incubate,
- discard the hexane phase,
- extract the matrix with n-hexane (repeat twice),
- multiple analyte extractions with MTBE/ethyl acetate 3:2 (v/v) and transfer of the organic phase to the drying vial,
- add phenylboronic acid solution,
- evaporate and derivatize in the mVAP (40 °C, 400 mBar) and finally
- the derivatives are taken up in Isooctane.
Dominik Lucas adds: “The analysis results we generated using the described automated method showed good correlation with reference analyses obtained from independent laboratories. Relative Standard Deviations for repeat analyses were at five percent for 3-MCPD and 6.4 percent for glycidol for the complete process”. As to using the described sample preparation and system solution for determination of 2-MCPD, 3-MCPD, glycidol and their fatty acid esters: “The evaporation step in the method means that users can reach the required sensitivity and stability even when using a single quadropole mass spectrometer,” Dominik Lucas states. The evaporation step ensures better sensitivity by concentrating analytes. In addition, it provides improved overall system stability by removing excess derivatization reagent before it can enter and destabilize the MS ion source.
503a www.efsa.europa.eu/en/panels/contam ISO 18363-1:2015 Animal and vegetable fats and oils – Determination of fatty-acid-bound chloropropanediols (MCPDs) and glycidol by GC/MS – Part 1: Method using fast alkaline transesterification and measurement for 3-MCPD and differential measurement for glycidol AOCS Official Method Cd 29b-13, Revised 2017: 2- and 3-MCPD Fatty Acid Esters and Glycidol Fatty Acid Esters in Edible Oils and Fats by GC/MS (Difference Method) DGF Unified Method C-VI 18 (10) (Available only in German language)
* G. Deußing, Press office Guido Deußing, 41464 Neuss/Germany