Highest isotope mass

Class 0 Highest isotope mass and nominal element mass coincide = wx-... 

Uranium is a very dense, highly reactive, metalhc element that has the highest atomic mass of the naturally occurring elements. Natnral nranium consists of two long-lived radioactive isotopes (99.28%) and U (0.72%). 

The actinides (Th, Pa, U) are the three naturally occurring elements with the highest atomic masses. None of these three has a stable isotope, which makes Th and Pa rare elements in the Earth s crust and sea water. In contrast, the uranium concentration in sea water is 12.6 nM, present as U(VI) in an oxyanionic soluble form. This oxyanion may serve as an electron acceptor for anaerobic respiration in bacteria (Lovley et al. 1991, Payne et al. 2002, Holmes et al. 2002). The resulting U(IV) is insoluble and can be precipitated by microbial cells (Yong and Macaskie 1998), which in turn opens up a biotechnological route for the bioremediation of uranium-contaminated environments. 

To obtain the highest precision, further precautions must be taken with sample handling, instrumental parameters, and electronics to minimize the noise levels. This makes the procedure highly complicated, and only a few laboratories in the world are able to perform such precise measurements. An example is the correction of the Avo-gadro number, based on isotope mass spectrometry with silicon isotopes (130]. 

The spectra obtained demonstrate sub-mg/L detection limits and high mass resolution (mass resolving power, m/A/nio%v = 7000-10000). For example, a 1 mg/L solution of copper yields a S/N of 8 for Cu (isotopic concentration 0.69 mg/L), clearly demonstrating sub-mg/L detection limits. The highest reported mass resolving power for an ICP-FTICR spectrum in this work is m/Am io% = 88 000, obtained for Ar". ... 

A further point about mass spectrometry, noticeable in the spectrum of propane (Figure 12.2), is that the peak for the molecular ion is not at the highest m/z value. There is also a small peak at M + l because of the presence of different isotopes in the molecules. Although 12C is the most abundant carbon isotope, a small amount (1.10% natural abundance) of 13C is also present. Thus, a certain... 

Molecular ion If a molecular ion is not observed, it can be deduced by adding 31 or 32 mass units to the highest peak observed (neglecting isotopes). 

The highest mass peaks observed in the mass spectra of alkyl chlorides may correspond to the loss of HX or X (loss of HI is seldom observed), depending on the structure of the molecule. In order to deduce the molecular ion, add the mass of X or HX to the mass at which the highest mass peak is readily observed. (Note that higher mass ions having the isotope pattern of X may be present... 

As a noble gas, Rn in groundwater does not react with host aquifer surfaces and is present as uncharged single atoms. The radionuclide Rn typically has the highest activities in groundwater (Fig. 1). Krishnaswami et al. (1982) argued that Rn and all of the other isotopes produced by a decay are supplied at similar rates by recoil, so that the differences in concentrations are related to the more reactive nature of the other nuclides. Therefore, the concentration of Rn could be used to calculate the recoil rate for all U-series nuclides produced by a recoil. The only output of Rn is by decay, and with a 3.8 day half-life it is expected to readily reach steady state concentrations at each location. Each measured activity (i.e., the decay or removal rate) can therefore be equated with the input rate. In this case, the fraction released, or emanation efficiency, can be calculated from the bulk rock Ra activity per unit mass ... 

In the case of isotopes, the isotope of greatest atomic mass has highest priority. 

The molecular ion peak directly provides valuable information on the analyte. Provided the peak being of sufficient intensity, in addition to mere molecular mass, the accurate mass can reveal the molecular formula of the analyte, and the isotopic pattern may be used to derive limits of elemental composition (Chaps. 3.2 and 3.3). Unfortunately, the peak of highest m/z in a mass spectrum must not necessarily represent the molecular ion of the analyte. This is often the case with El spectra either as a result of rapidly fragmenting molecular ions or due to thermal decomposition of the sample (Chaps. 6.9 and 6.10.3)... 

The molecular ion must be the ion of highest m/z in the mass spectrum (besides the corresponding isotopic peaks). 

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