Isotopes, interfering

Element The most abundant isotopes Interfering species... 

Although cold plasmas have benefits in removing interfering ions such as ArO+, they are not necessary for other applications where interferences are not a problem. Thus, in laboratories where a range of isotopes needs to be examined, the plasma has to be changed between hot and cold conditions, whereas it is much simpler if the plasma can be run under a single set of conditions. For this reason, some workers use warm plasmas, which operate between the hot and cold conditions. 

Tracers have been used to label fluids in order to track fluid movement and monitor chemical changes of the injected fluid. Radioactive materials are one class of commonly used tracers. These tracers have several drawbacks. One drawback is that they require special handling because of the danger posed to personnel and the environment. Another drawback is the alteration by the radioactive materials of the natural isotope ratio indigenous to the reservoir— thereby interfering with scientific analysis of the reservoir fluid characteristics. In addition, the half life of radioactive tracers tends to be either too long or too short for practical use. 

Not only components from the set A,...,N can interfere with the analytes but also additional species which may be partly unknown or will be formed during the measuring process. Such situations occur especially in ICP-MS, where the signal of an isotope A, may be interfered by isotopes of other elements, Bj, Q etc., and additionally by molecule ions formed in the plasma (e.g., argon compound ions and ions formed from solvent constituents). 

Figure 9.5 ICP-MS survey data from masses 203 to 210. The vertical columns show the expected positions and relative abundances of the four natural isotopes of lead (204Pb, 1.4% 206Pb, 24.1% 207Pb, 22.1% 208Pb, 52.4%). The agreement between the survey data (dotted line) and the actual abundance of lead confirms that lead is present, and that there are no significant interfering elements.

Wiedmeyer (1998). One method of testing for interference is to examine the survey data. In this type of analysis a large number of points are recorded across the mass range, rather than a single measurement taken at a particular mass number for each element. Figure 9.5 shows survey data (dashed line) for masses 203 to 210 on a sample believed to contain lead. The natural lead isotopic abundance is superimposed, shown by filled columns. The proximity of the survey data to the actual abundance of lead indicates that lead is present, and that no interfering elements are present. In this case, a single measurement at mass 208 (which is used for most analyses of lead) is sufficient to quantify lead in the sample. 

Brereton N. R. (1970). Corrections for interfering isotopes in the °Ar/ Ar dating method. Earth Planet. Scl Letters, 8 427-433. 

The stable-isotope dilution GC-MS measurement of GA and Cr in plasma, CSF and urine is sensitive, robust and reliable. The measurement of especially GA in CSF needs attention with regard to the chromatography. The analyses should be carried out on a GC column coated with a polar stationary phase to achieve proper separation of GA and interfering compounds. 

Isobaric overlaps appear when isotopes of different elements have the same nominal mass. Many of them can be overcome by choosing an alternative less interfered isotope of the element of interest, although a sacrifice in sensitivity may result. 

Table II summarizes the parameters which relate to the measurement of each element neutron activation products, half-lives, y-ray energies, lengths of irradiation, decay, and counting. Also listed are the possible interfering radionuclides and interfering reactions producing the same isotopes from another element which were necessarily evaluated. This table is subdivided into three sections representing the elements determined during each of the three counting intervals.

ELEMENT TARGET ISOTOPE ISOTOPIC ABUNDANCE (%) PRODUCT NUCLIDE HALF- LIFE THERMAL NEUTRON CROSS SECTION BEST y FOR MEASUREMENT (KEV) NUMBER OFy s PER 1000 DECAYS ASSOCIATED y -RAYS KEV MEASUREMENT POSSIBLE INTERFERING NUCLEAR REACTIONS PRODUCING NUCLIDES OF INTEREST... 

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