There are several papers presenting results of the studies on alleviating iron deficiency anemia by oral dosage of iron. Most preparations contain iron in the form of salts or chelates of Fe(II), less frequently as Fe(III) compounds. Some foods are fortified with iron by using Fe(II) and Fe(III) compounds. In our study, we aimed to focus on a frequently disregarded aspect of iron bioavailability, i.e. chemical speciation of iron in the gastrointestinal tract. Chemical speciation of iron was predicted using the chemical equilibrium model Visual MINTEQ. Fe speciation calculations were carried out for ferrous bis-glycinate, ferrous sulfate and ferric sodium ethylenediaminetetraacetate. The ionic equilibrium calculations were carried out for a wide range of pH (1÷8), from low values (pH 1÷2) so as to recreate the gastric environment, to pH 5÷8 in order to match the environment in the small intestine. Under assumed gastrointestinal conditions, Fe(II) was the only thermodynamically stable form of dissolved iron. Ferrous sulfate and ferrous bis-glycinate were characterized by very similar speciation of iron in the model gastric juice. The main form of dissolved ferrous iron were aqua-complexes of Fe(II). Poor complexing properties of the glycinate anion became apparent only in a slightly alkaline medium. The presence of phosphate anions limited full solubility of Fe(II) to acidic pH. The speciation prediction of dissolved Fe in NaFeEDTA solutions included virtually only anionic Fe(II)-EDTA complexes. Slight precipitation of Fe occurred only at pH 8. In more complex systems, where other divalent cations forming stable complexes with EDTA (e.g. Zn2+ and Ca2+) are present, competitive complexation reactions may lead to an essential change in Fe speciation in neutral and weakly alkaline solutions. The deficit of EDTA available for Fe(II) resulted in precipitation of sparingly soluble Fe compounds.

23.3.2018