ELEMENTAL SPECIATION WITH LIQUID-CHROMATOGRAPHY INDUCTIVELY-COUPLED PLASMA ISOTOPE-DILUTION MASS-SPECTROMETRY

For the determination of elemental species, which normally exist at low concentrations in the environment, coupling of liquid chromatographic systems with inductively coupled plasma mass spectrometry (ICP-MS) is a powerful method with respect to detection limit. However, accurate results are still a problem in trace analyses but can be obtained by the application of isotope dilution mass spectrometry (IDMS). The developed LC-ICP-IDMS system consists of a high-performance liquid chromatography pump, a sample injection valve, a separation column (different types of chromatographic separation systems, e.g., ion or size-exclusion chromatography, were used depending on the separation problem), a non-destructive detector (e.g. a UV detector) for simultaneous determination of organic substances, and an element-specific ICP mass spectrometer. Isotope dilution is carried out by adding an isotopically enriched species-specific spike solution to the sample prior to the separation step in the case of the determination of well-defined species, or by continuous on-line introduction of a species-unspecific spike solution in the case of species with unkown composition and structure. The species-specific spiking method is demonstrated for the determination of iodide and iodate in mineral water using an ion chromatographic separation column. For example, iodate concentrations in the range of 0.5-20 ng ml(-1) could be determined with relative standard deviations of about 2%. The species-unspecific spiking mode is used to determine heavy metal complexes with humic substances at a level of about 1 ng ml(-1) as well as organo-iodine species in the concentration range 0.7-1.4 ng ml(-1) in natural water systems. The accuracy of speciation could be verified by comparing the total element concentration with the sum of the different elemental species.