Isotope dilution mass spectrometry lead analysis

Isotope dilution mass spectrometry (cf. (Heumann, 1992 Yu et al., 2002)) has two main requirements. The first is that the element being analyzed must have more than one isotope. The second is to have a well-characterized and pure tracer solution that has a significantly different isotopic composition from the element under analysis. In practice, a known amount of the tracer is added to the sample, which is then treated by any necessary chemical separations before being inserted into the mass spectrometer. The tracer must be isotopically equilibrated with the sample by forcing them into a common valence state, as discussed in Section 4.7. For elements with multiple valence states (such as uranium or plutonium) this is a crucial requirement. Failure to achieve isotopic equilibration will lead to erroneous results. Sample quantitation by isotope dilution can be determined by use of the following general equation ... 

Isotope Dilution Mass Spectrometry (IDMS). Lead concentrations are only approximated with any analytical technique, since there is no method that can measure the true concentration of any element in any matrix. The most accurate concentration measurements are made with definitive methods, including isotope dilution mass spectrometry (IDMS) using TIMS. Isotope dilution TIMS is considered the definitive method because it is a yield-independent method of analysis, extremely sensitive, and precise (Webster 1960). The analysis is capable of distinguishing lead from false... 

Spark source (SSMS) and thermal emission (TEMS) mass spectrometry are used to determine ppb to ppm quantities of elements in energy sources such as coal, fuel oil, and gasoline. Toxic metals—cadmium, mercury, lead, and zinc— may be determined by SSMS with an estimated precision of 5%, and metals which ionize thermally may be determined by TEMS with an estimated precision of 1% using the isotope dilution technique. An environmental study of the trace element balance from a coal-fired steam plant was done by SSMS using isotope dilution to determine the toxic metals and a general scan technique for 15 other elements using chemically determined iron as an internal standard. In addition, isotope dilution procedures for the analysis of lead in gasoline and uranium in coal and fly ash by TEMS are presented. 

In the last decade or two, the advent of new instrumentation directed at elemental analysis has provided fertile new ground for expanded use of isotope dilution. Glow discharge mass spectrometry is in many ways the modem replacement for spark source and has similar impediments to ready application of isotope dilution. A recent report of Barshick et al. describes assaying lead in oil residues using the technique [21]. The obstacles spark source and glow discharge mass spectrometry both present to ready use of isotope dilution make it unlikely that widespread application of the technique will occur in conjunction with them. 

J. R. Dean, L. Ebdon, R. C. Massey, Isotope ratio and isotope dilution analysis of lead in wine by inductively coupled plasma-mass spectrometry, Food Addit. Contam., 7 (1990), 109-116. 

Of the various analytical techniques, methods using mass spectrometry with isotope dilution play a special role. Initially they were used for determination of inorganic analytes, but later, in the last decades of twentieth century, they were also used for the analysis of organic species. These methods require the use of isotope-labeled compounds, but lead to very good precision and accuracy, as required in definitive procedures [14]. 

Table 1. Lead contamination blanks for serum collection, processing, and analysis by isotope dilution thermal ionization mass spectrometry in the WIGS Trace Metal/Mass Spectrometry facihty. University of California, Santa Cruz. Lead values are based upon repeated measurements.

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