Human breast milk can be considered as "ideal" food for the correct development of newborn babies and, for those that are not breast-fed, formula milk has to be used instead. Ideally, the composition of such formula milk preparations should closely resemble that of maternal human milk. Considerable differences between both in the total content of trace elements such as Fe, Cu, Se, Zn, and I and in their chemical form in both milk types have been demonstrated.Speciation analysis in milk whey was carried out first by high-performance liquid chromatography (HPLC) with inductively coupled plasma-mass spectrometry (ICP-MS) elemental detection and showed that the observed element distribution patterns were very different in the investigated human and formula milks. Using complementary molecular mass techniques (i.e., MALDI-TOF), the identity and chemical characterization of some biomolecules (e.g., protein) with which metals are associated in each fraction was also established (by a typical heteroatom-tagged proteomics protocol). Attempts to assess the nutritional value of elemental supplements in formula milk with the aid of quantitative chemical speciation, using stable isotopes in combination with ICP-MS and isotope pattern deconvolution (IPD), proved to be successful to differentiate and quantify endogenous (natural) and exogenous (supplemented) Se or Fe trace levels. In particular, the application of such ICP-MS based techniques to study Se bioavailability from formula milk and metabolism in Se-supplemented lactating rats is discussed in detail. Quantification of selenospecies of endogenous (natural) and exogenous (supplement) Se in rat's urine is demonstrated and relevant information on possible Se biotransformations and its final catabolism from such results is discussed.The determination of essential and toxic trace elements in nutrition has acquired great importance [1]. However, elements may occur in food in many chemical forms, i.e., as building blocks of essential macronutrients (e.g., proteins, carbohydrates, lipids, etc.) and micronutrients (e.g., vitamins, enzymes) and as minerals and trace elements. Today it is widely recognized that the nature and amount of a given element chemical species in a food matrix, rather than the corresponding element total analytical concentration, will determine its bioavailability (e.g., in human milk), metabolism, transport/storage in the body, and eventually its biochemical essential role and so its nutritional value. The precise definitions of the different terms including "speciation analysis" and "chemical species" are given elsewhere [2]. In other words, chemical element species information (apart from total elemental concentration) is needed for a sound assessment of how the considered element is absorbed, retained, metabolized, etc. and to decide whether its effects are beneficial (essential elements), toxic, or rather the element has no adverse impact at a specific concentration, but it can become a therapeutic drug at higher levels of concentration [3]. In brief,...
