Use of an ion selective electrode to determine the complexing of copper in food extracts dependent upon the pH

Speciation affects the bioavailability of elements and is very important in nutrition. In fact, it can provide knowledge about absorption, distribution, reactivity to binding sites, bioavailability, toxicity and excretion of elements. Availability for absorption depends upon the characteristic chemical state of the intestinal mucosa cells, namely the solubility, oxidation state and binding strength of ligands in the lumen of the gastrointestinal tract. Crucially important for the resorption of the elements from food is the chemical form of complexes in which the element is present. The elements exist probably not in the intestine as free ions, but as a complex partner. The organic and inorganic components of food that can bind with elements affect the transport of the latter and consequently their resorption in the intestine. This phenomenon essentially depends on the pH, the concentration of the element as well as the chemical ratio. Potentiometric measurements with an ion selective electrode (ISE) were made to determine the copper species in food samples. Different model solutions containing copper, and organic or inorganic substances of food, which form pH dependent complexes with copper ions, were potentiometrically analysed by means of a copper selective electrode to determine the dominant binding partners. The above mentioned method is suitable to characterise and quantify the bioavailability and main binding partners of copper both of which are dependent upon the pH in foodstuffs. The results obtained provide information concerning the resorption of copper when food moves from the acid pH environment of the stomach to the alkaline milieu of the small intestine.