Isotope dilution analysis species-unspecific

The application of isotope dilution analysis to ICP-MS-based hyphenated techniques, for example HPLC-ICP-MS, can be divided into two diflerent modes the spedes-unspecific mode and species-specific mode. The two modes are illustrated in Figure 4.6. Because IDA-ICP-MS relies on the measurement of isotope ratios by mass spectrometry, the traditional interference to the accuracy and precision of IDA should all be considered and some biases need further correction in this case, such as spectral interferences, dead time of detector, mass discrimination, and statistic and stability of ion counting. 

Later, Busto et al. used synthesized Fe-labeled transferrin to determine individual transferrin isoforms in human serum samples for the species-specific mode. The stability of the prepared proteins was tested for 1 week and no iron exchange had occurred. They concluded that the results are in good agreement with other calibration methods, e.g. the species-unspecific method however, the species-spedfic mode can offer better precision. Hoppler et al. also synthesized and characterized Fe-labeled Phaseolus vulgaris ferritin for isotope dilution analysis. " ... 

In the last few years, we have seen the application of isotope dilution methodologies to some new analytical fields. One of these is elemental speciation , where the aim is to determine individual chemical species in which an element is distributed in a given sample. IDMS has also proved its usefulness in element speciation, in which either species-specific or species-unspecific spikes can be used. For example, species-specific IDMS is nowadays used in several laboratories as an effective tool to validate analytical procedures for speciation and to investigate and document eventual interconversion between species. In addition, the study of induced variations in the isotopic composition of a target element can also provide insight into various (bio)chemical and physical processes isotopic analysis is, therefore, also of increasing importance in biological studies. 

Chapters on sample introduction and hyphenated sample treatment and ICP systems have also been further updated since the last edition. No doubt that chromatographic, electrophoresis, flow injection and field flow fraction separations have extended ICP-MS (and AES) measurements as the mainstay of elanental specia-tion measurements in biological and environmental fields. Without the combination of these separation techniques and ICP measurements, elemental speciation applications would be severely hampered... if not impossible (Chapter 18). The ability to measure P and S with high sensitivity has opened up new opportunities in proteomics, for example. Species-specific and unspecific isotopic dilution (ID-MS) has been critical in quantifying speciation analysis and revealing recovery errors (Chapter 13). Species-specific techniques have been applied to identify species transformations, resulting in the development of multi-species methods whereas, hyphenated species-unspecific ICP-ID-MS determinations of heteroatoms such as sulfur have become a common quantification technique in proteomics. 

In species-unspecific isotope dilution techniques, an isotopically enriched standard solution is added post-column, and the data evaluation is performed as described in Section 7.3.4 for CE coupling. Species-unspecific isotope dilution for HPLC coupling has been described for the determination of Cd, Cu and Zn in metallothioneins extracted from eel liver, while Fe, Cu and Zn were determined in proteins separated from human serum. This technique has also been applied to iodine determination in humic substances,as well as selenium speciation in human serum. Species-specific isotope dilution using HPLC-ICP-MS has been described for selenium analysis, the analysis of organotin species in sediments, methylmercury in fish tissue, trimethyllead in water, and chromium speciation. Overviews to this topic have been published, e.g. by Heumann and Hill. ... 

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