6. AOACSPIFANMethods-2018Awards

326

AOAC Official Method 2018.12 2-Monochloropropanediol (2-MCPD), 3-Monochloropropanediol (3-MCPD), and Glycidol in Infant and Adult/Pediatric Nutritional Formula Gas Chromatographic/Mass Spectrometric (GC/MS) Method First Action 2018

[Applicable for determination of the overall (total) contents of free and ester-bound 2-MCPD, free and ester-bound 3-MCPD, and ester-bound glycidol in powdered and liquid infant formula and adult nutritionals.] Caution : Refer to Material Safety Data Sheet prior to use of chemicals. Use appropriate personal protective equipment when performing testing. Perform solvent evaporation procedures under a fume hood. A. Principle Free and ester-bound (bound) analytes are extracted from a powdered test sample by triple heat- ultrasonic-pressure-supported-solvent-extraction (HUPsSE) using methanol and tert -butyl-methyl-ether (tBME), which cover the polar to the non-polar range of the analytes. After subsequent application of a liquid/liquid (l/l)-extraction, the combined extracts are separated into an aqueous polar fraction containing free 2- and 3-MCPD and a non-polar fraction containing lipids and bound 2- and 3-MCPD and bound glycidol. Additionally, this separation step also aids in matrix removal. The free analytes are transferred into an organic phase by l/l-extraction. For liquid test samples, the non-polar fraction containing lipids and the ester bound 2- and 3-MCPD and ester bound glycidol is isolated by a l/l-extraction approach according to Röse-Gottlieb. In a second analysis, the free analytes in liquid test samples are transferred into an organic phase by l/l extraction after acidic protein denaturation. If it is desired to apply the same sample preparation procedure to both powdered and liquid samples, liquid test samples may be converted to powders by lyophilization and the HUPsSE approach can be applied. Additionally, powdered formula samples may be reconstituted to liquids by following the preparation instructions on the label and then prepared using the specified sample preparation for liquid test samples. The latter procedure has been evaluated in the corresponding SLV. Liquid concentrates are also covered by this method assuming they are diluted to a degree that corresponds to consumable liquid infant formula. In each case, the free analytes (2- and 3-MCPD) are derivatized by use of phenylboronic acid (PBA) and measured as corresponding PBA-derivatives by GC/MS. According to an adapted application of an established method, the non-polar lipid fractions containing the ester bound analytes undergo a mild alkaline catalyzed transesterification in order to release the core analytes in free form. Subsequently, the highly reactive glycidol is converted into stable monobromopropanediol (MBPD) by reaction with acidified sodium bromide solution. Removal of the lipid matrix is carried out by l/l-extraction and the remaining analytes (ester-bound 2-MCPD, ester-bound 3-MCPD and ester-bound glycidol) are transferred into an organic phase where they are derivatized by use of PBA and measured as corresponding dioxaborolane derivatives by GC/MS. Quantification is carried out via internal one-point-calibration using the corresponding penta-deuterated compound as internal standard (surrogate standard) for each analyte. Any undesired conversion of 3-MCPD into glycidol during alkaline catalyzed transesterification is corrected