Isotope dilution species-unspecific method

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. " ... 

This technique has been used for a variety of element species, such as trimethyl- and triethyl-lead, organotins, iodine, methylmercury, and chromium. With HPLC, isotope dilution has been performed with species-specific as well as species-unspecific methods. 

Dimethyl-Tl (Me2Tl ) was determined in 500 ml sea water samples by combining Isotope Dilution Mass Spectrometry (IDMS) with a species-specific extraction method (18). A ° Tl-enriched spike solution was applied for the isotope dilution step and the production of positive thermal ions was used for mass spectrometric measurements. After species-unspecific T1 enrichment at an anion exchanger, inorganic T1 was oxidized to Tl(III) by a Br2 solution and then separated by extraction with methyl xo-butyl ketone, whereas Me2Tl remained in the aqueous phase. The detection limit for Mc2Tl is 440 pg 1 (as Tl). 

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. 

The method of the species-unspecific modes is well described in literature. In brief, isotope ratios are monitored during the whole chromatographic procedure and corrected by the isobaric interference, dead time, and mass bias. Then the chromatogram of isotope ratios is transformed into the chromatogram of mass flow (mass versus time) using the following isotope dilution equation ... 

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