AOAC 2018 Methods

(e) Working solution 3.— 2-MCPD-1,3-dipalmitoyl ester, 3-MCPD-1,2-dioleoyl ester and glycidyl-oleate with 5 µg/mL 2-MCPD equivalent, 10 µg/mL 3-MCPD equivalent and 5 µg/mL glycidol equivalent in toluene (f) Working solution 3d .—d 5 -2-MCPD-1,3-dipalmitoyl ester, d 5 -3-MCPD-1,2-dioleoyl ester and d 5 -glycidyl oleate with 5 µg/mL d 5 -2-MCPD equivalent, 10 µg/mL d 5 -3-MCPD equivalent and 5 µg/mL d 5 -glycidol equivalent in toluene (g) Working solution 4d .—d 5 -3-MCPD-1,2-dioleoyl ester, 10 µg/mL d 5 -3-MCPD equivalent in toluene (h) Working solution 5 .—Glycidyl oleate, 1 µg/mL in toluene Note: The purity of standard compounds should be verified according to common practice. In the author´s experience, the non-labelled standard compounds can typically be purchased in sufficient amount and purity, but it is recommended that the isomeric purity of the bound MCPD isomers is verified by GC-MS analysis according to section D. In contrast, the purity of the isotope-labelled standards may not be as well-defined. To overcome the expensive determination of potential impurities in isotope-labelled analyte samples (preferably by LC, GC and NMR techniques), concentrations can be adjusted against the non- labelled compounds. Therefore, for each analyte, aliquots of accurately prepared non-labelled stock solutions are mixed with the same volume of a raw stock solution of the corresponding deuterium-labelled analyte at approximately the same concentration level. These mixtures are analyzed in the presence of a blank matrix according to section D in order to determine the concentration of the isotope-labelled analytes by using the corresponding non-labelled compounds as internal quantification standards. The working solutions of the isotope-labelled internal standards can then be prepared by dilution of the crude stock solutions. Subsequently, concentrations of isotope-labelled internal standards in the mixed working solutions should be checked against the non-labelled analyte working solution mix in the same manner. By this procedure, any differences in the GC-MS response of isotope-labelled internal standards and non- labelled analytes will be compensated for as well. This check should be repeated whenever a new GC-MS system is used. E. Determination of Free 2-MCPD, Free 3-MCPD, Ester-Bound 2-MCPD, Ester-Bound 3-MCPD and Ester- Bound Glycidol in Powdered Infant Formula and Adult Nutritionals (a) Powdered samples.—Extraction procedure and analyte separation.—(1) Weigh between 1.99 and 2.01 g of sample in a 12 mL screw cap vial. Add 100 µL standard working solution 2d (with 1.0 µg/mL 2-MCPD equivalent and 1.0 µg/mL 3-MCPD equivalent in methanol, resulting in a sample concentration of 50 µg/kg each) and 200 µL standard working solution 3d (with 5 µg/mL d 5 -2-MCPD equivalent, resulting in a sample concentration of 250 µg/kg; 10 µg/mL d 5 -3-MCPD equivalent, resulting in a sample concentration of 500 µg/kg; and 5 µg/mL d 5 -glycidol equivalent in toluene, resulting in a sample concentration of 250 µg/kg). (2) Subsequently, add 6 ± 1 mL methanol to each sample. Shake the closed vessel immediately after methanol addition to minimize clumping later. Tightly seal the screw cap vial and start the extraction by placing the vessel in a plastic rack horizontally for 15 min in the ultrasonic bath at a starting temperature of 65°C. Place a cover on the bath during ultrasound treatment and avoid direct contact of the glass body to the walls of the ultrasonic bath as this might cause the glassware to burst. However, because the vessels are covered by water, which exhibits a strong deceleration ability, there is no need for special safety measures.