Determination of Ca, Mg, Fe and Zn partitioning in UHT cow milks by two-column ion exchange and flame atomic absorption spectrometry detection.

An operationally defined fractionation protocol was developed to study the partitioning of Ca, Mg, Fe and Zn in UHT cow milks. The method was based on sorption of distinct metal species by two ion exchange columns, namely strong cation exchanger Dowex 50Wx4 and strong anion exchanger Dowex 1x4, connected in a series. The evaluation of the donation of metal species classes distinguished, that is cationic and anionic fractions, was made after splitting the columns and elution of metal groupings with a 2.0mol l(-1)HCl solution, followed by the determination of metal concentrations in the resulting eluates. The amount of third, inert fraction was assessed by measuring metal contents in the effluents obtained after passage of the samples through the columns. The results achieved utilizing two-column ion exchange based procedure were compared with those obtained for the approach in which the columns were considered separately. The fractionation pattern for each metal studied was thoroughly discussed in light of available knowledge relating to the composition of milk.