The movement of an ion in an aqueous homogenous electrolyte in an electrical field gives a physico-chemically unique parameter: the absolute individual ion mobility. The tracer-principle of nuclear chemistry allows us by using very small amounts of mass of the radioactive ions to record their migration with high accuracy using radiation detectors. The measured mobility of the ion is an experimental function of the type (composition) of the electrolyte and its ionic strength. It is possible to determine the characteristic individual ion mobility of any ion in its corresponding electrolyte. These parameters reflect the ion-ion- and ion-dipole-interactions. The individual ion mobility can be extrapolated to a value at infinite dilution of the electrolyte. Ion mobility values can be transformed int. Diffusion and conductivity coefficient. Additional variation of the inert composition of the electrolyte by addition of complex ligands or pH-variation allows for the experimental determination of complex formation equilibrea as well as hydrolysis or protonating constants.