Isotope abundance table

So far we have treated the X-f1 and the X-f2 elements separately, which is not how they are encountered in most analytes. The combination of C, H, N and O with the halogens F, Cl, Br and I covers a large fraction of the molecules one usually has to deal with. When regarding H, O and N as X elements, which is a valid approximation for not too large molecules, the construction of isotopic patterns can be conveniently accomplished. By use of the isotopic abundance tables of the elements or of tables of frequent combinations of these as provided in this chapter or... 

Fig. 5.5. Decomposition of Solar System abundances into r and s processes. Once an isotopic abundance table has been established for the Solar System, the nuclei are then very carefully separated into two groups those produced by the r process and those produced by the s process. Isotope by isotope, the nuclei are sorted into their respective categories. In order to determine the relative contributions of the two processes to solar abundances, the s component is first extracted, being the more easily identified. Indeed, the product of the neutron capture cross-section with the abundance is approximately constant for aU the elements in this class. The figure shows that europium, iridium and thorium come essentially from the r process, unlike strontium, zirconium, lanthanum and cerium, which originate mainly from the s process. Other elements have more mixed origins. (From Sneden 2001.)... 

Table 2.1 lists the principal stable isotopes of the common elements and their relative abundance calculated on the basis of 100 molecules containing the most common isotope. Note that this presentation differs from many isotope abundance tables, in which the sum of all the isotopes of an element adds up to 100%. 

Table 7.75 Isotopic Abundances and Masses of Selected Elements 7.124...

Natural Isotopic Abundances. The relative abundances of natural isotopes produce peaks one or more mass units larger than the parent ion (Table 7.75a). For a compound C H O N, a formula allows one to calculate the percent of the heavy isotope contributions from a monoisotopic peak, Pto the Pm + 1 peak ... 

Boron [7440-42-8] B, is unique in that it is the only nonmetal in Group 13 (IIIA) of the Periodic Table. Boron, at wt 10.81, at no. 5, has more similarity to carbon and siUcon than to the other elements in Group 13. There are two stable boron isotopes, B and B, which are naturally present at 19.10—20.31% and 79.69—80.90%, respectively. The range of the isotopic abundancies reflects a variabiUty in naturally occurring deposits such as high B ore from Turkey and low °B ore from California. Other boron isotopes, B, B, and B, have half-Hves of less than a second. The B isotope has a very high cross-section for absorption of thermal neutrons, 3.835 x 10 (3835 bams). This neutron absorption produces alpha particles. 

Properties of T2O. Some important physical properties of T2O are Hsted in Table 2. Tritium oxide [14940-65-9] can be prepared by catalytic oxidation of T2 or by reduction of copper oxide using tritium gas. T2O, even of low (2—19% T) isotopic abundance, undergoes radiation decomposition to form HT and O2. Decomposition continues, even at 77 K, when the water is fro2en. Pure tritiated water irradiates itself at the rate of 10 MGy/d (10 rad/d). A stationary concentration of tritium peroxide, T2O2, is always present (9). AH of these factors must be taken into account in evaluating the physical constants of a particular sample of T2O. 

From the isotope abundances listed in Table 2.1, it is obvious that the M + 2 ion abundance in this example is due to two chlorine atoms. 

Applications Table 8.58 shows the main fields of application of inorganic mass spectrometry. Mass-spectrometric techniques find wide application in inorganic analysis, and are being used for the determination of elemental concentrations and of isotopic abundances for speciation and surface characterisation for imaging and depth profiling. Solid-state mass spectrometry is usable as a quantitative method only after calibration by standard samples. 

Table 1 Physical constants Isotopic abundance Half-life...

Since only one or two charge states are observed for any element, the elemental identity of each ion is determined from its mass-to-charge ratio by consulting a table of known isotope abundances. 

Table 2.5 Natural isotopic abundances and monoisotopic masses of common elements...

G. W. C. Kaye and T. H. Laby, Tables of Physical and Chemical Constants, Longman 1995, gives a table of properties of the nuclides including isotopic abundance or half-life, decay modes, mass excess, neutron capture cross-section and ground-state spin and parity. This publication, with a prospect of regular updates, is available on the website http //www.kayelaby.npl.co.uk/. 

Table 5.4 represents natural isotopic abundances of the most important (for organic compounds) elements. This table is a fragment of the complete table of isotopes of... 

TABLE 5.4. Natural Isotopic Abundances of Widespread Chemical Elements... 

TABLE A.1. Exact Masses and Isotopic Abundances of Selected Elements... 

Table 5.1. Ion beam intensities Tj (mV) at mass i, isotopic abundances a of metals and...

Isotopic abundances are listed either as their sum being 100 % or with the abundance of the most abundant isotope normalized to 100 %. The latter is used throughout this book because this is consistent with the custom of reporting mass spectra normalized to the base peak (Chap. 1). The isotopic classifications and isotopic compositions of some common elements are listed below (Table 3.1). A full table of the elements is included in the Appendix. 

Example The presence or absence of the polyisotopic element tin (Table 3.1) can readily be detected from its characteristic isotopic pattern. In case of tetrabutyltin, Ci6H3gSn, the lowest mass isotopic composition is CieHse Sn, 340 u. Due to the 16 carbon atoms, the isotopic abundance is about 17.5 %. This is superimposed on the isotopic pattern of elemental Sn, which becomes especially... 

Table 1.1 Isotopic abundance of common elements. Interesting to note is that chlorine and bromine have t /o naturally intense isotopes.

Table 11.2 Naturally occurring radioactive substances, a = years, d = days. Radionuclide Decay Process Half-Life Isotopic Abundance (%) Stable End-Product...

The accuracy with which absolute isotope abundances can be measured is substantially poorer than the precision with which relative differences in isotope abundances between two samples can be determined. Nevertheless, the determination of absolute isotope ratios is very important, because these numbers form the basis for the calculation of the relative differences, the 5-values. Table 1.6 sununarizes absolute isotope ratios of primary standards used by the international stable isotope community. 

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