Speciation of zinc in low molecular weight proteins of breast milk and infant formulas by size exclusion chromatography/flame atomic absorption spectroscopy

Size exclusion chromatography (SEC) and flame atomic absorption spectroscop y (FAAS) were used for the separation of metal-containing species in milk w hey. After milk ultracentrifugation, the sample was injected into a TSK-Gel G2000 glass column and eluted with 0.2M NH4NO3-NH3, pH 6.7, Low molecular weight proteins were fractionated, and the fractions were characterized by molecular weight. Zinc distributions were obtained by FAAS using a high per formance nebulizer, The method was very sensitive (limit of detection = 2.6 x 10(-3) mug/mL; limit of quantitation = 8.9 x 10(-3) mu /mL) and precise (RSDs less than or equal to 10%), This method was applied to the determinat ion of Zn in binding compounds in breast milk whey and in commercial cow's milk-based formulas, Distribution patterns were different. The presence of Zn in most fractions in breast milk was most significant, whereas in infant formulas Zn was detected only in fractions of molecular weight <5 kDa and in the highest molecular weight peak.