The aim of the presented thesis was the suggestion and verification of the method for determination As(III) in water samples, study of metal compounds interaction with biologically important molecules using electrochemical methods, and electrochemical detection of iron and selenium in biological samples. Electrochemical detection of As(III) was performed on the glassy carbon electrode modified by gold nanoparticles and graphene oxide. This modification led to the increase of detected signal more than 50%. Interaction of metal compounds with biomolecules was represented by the studies focusing on the interaction of platinum cytostatics with G-quadruplexes and interaction of these cytostatics with metallothionein. For electrochemical determination of iron automatic procedure was suggested and tested. As samples erythrocytes from MeLim minipigs were used. Influence of selenium form in food intake at postpartum sows was studied through determination of selenium in erythrocytes.