Isotopic analysis of the essential transition metals Fe, Cu and Zn in human blood via multi-collector ICP-MS after their chemical isolation. Characterization of the spread in the isotope ratios of Fe, Cu and Zn in the reference population and identification of the governing factors. Comparison of the isotopic composition of Fe, Cu and Zn in blood from the reference population to the corresponding values in patient populations. Evaluation of the capabilities of this type of isotopic analysis as a diagnostic tool.