Determination of fatty acid contents in infant formula by isotope dilution-gas chromatography/mass spectrometry

An isotope dilution-gas chromatography/mass spectrometry (ID-GC/MS) method was developed as a candidate reference method for the accurate determination of the amount of fatty acids in infant formula. C-13- or H-2-labeled fatty acids were used as internal standards to correct for recovery and instrument sensitivity during sample preparation and MS measurements, respectively. The developed ID-GC/MS method was validated based on the repeatability and reproducibility of selected fatty acid analyses. For fatty acid measurements in a homogenized infant formula, the repeatability and the reproducibility were < 2.0% and < 3.0%, respectively. In addition, the developed method provided relative expanded uncertainties of 1%-6% for analyses of target fatty acids indicating a higher-order metrological quality. The developed method was successfully applied to evaluate the fatty acid contents of five commercial infant formulas and to determine the stability of homogenized infant formula under different storage conditions.