Natural abundance, stable isotopes

E.J. Winkler (1984) Application of natural abundance stable isotope mass spectrometry in food control. In A. Erigerio, H. MUon (eds.) Chromatography and Mass Spectrometry in Nutrition Science and Eood Safety. Elsevier Science Publishers, Amsterdam, pp. 173-190... 

All organic molecules contain a significant amount of (natural abundance 1.1% of C) and much lesser amounts of (natural abundance 0.015%) and, where relevant, (natural abundance 0.36%). The presence of naturally abundant stable isotopes within a molecule ultimately limits the amount of precursor label which can be detected in a metabolite. This is particularly true where the most abundant isotope, is involved. Enhanced signals in the... 

Jim, S., Ambrose, S. H. and Evershed, R. P. (2003b) Natural abundance stable carbon isotope evidence for the routing and de novo synthesis of bone FA and cholesterol. Lipids 38, 179 186. 

The nominal mass is defined as the integer mass of the most abundant naturally occurring stable isotope of an element. [3] The nominal mass of an element is often equal to the integer mass of the lowest mass isotope of that element, e.g., for H, C, N, O, S, Si, P, F, Cl, Br, I (Table 3.1). The nominal mass of an ion is the sum of the nominal masses of the elements in its empirical formula. 

Symbol B atomic number 5 atomic weight 10.811 a Group III A (Group 13) metalloid element atomic volume 4.70 cc/g-atom electron affinity 0.277 eV electronic configuration Is22s22pi valence state +3 naturally occurring stable isotopes are B-10 and B-11 and their abundance 19.57% and 80.43%, respectively. 

Furthermore, isotope analysis is relevant for determining the atomic weight (Ar(E)) of elements. The Ar(E) is the average of all masses of all naturally occurring stable isotopes (taking into account the abundances of isotopes) of a chemical element (see Appendix I10). By consideration of the masses of isotopes (/ ,) and the known relative abundances of all stable isotopes (Xi) with i = 1 to n of a selected chemical element, the average atomic weight (Ar(E)) of this element can be calculated ... 

Natural Abundance. The isotopic abundances listed are on an atom percent basis for the stable nuclides present in naturally occurring elements in the earth s crust. 

Natural Abundance Stable Carbon Isotopes (I3C). There are trends in 13C of plant, litter, and organic constituents in soil that can be used to investigate carbon cycling, but to date the trends have proven too subtle, the variation too high, or the mechanisms too poorly understood to exploit these patterns definitively. The 813C of plant litter and particulate SOM is typically close to that of the plant source,... 

Atoms that have the same atomic number (Z) but different atomic mass numbers (A) are termed isotopes [1]. Isotopes are classified into atoms that are unstable and decay by emission of radiation to stable products (radioisotopes) and those that have never been observed to decay (stable isotopes). Most of the elements associated with organic compounds possess naturally occurring stable isotopic variants. Stable isotopes frequently encountered in the course of pharmacokinetic and drug-metabolism studies and their natural abundances, relative to the most abundant mass, are listed in Table 1 [2,3]. 

Stable isotopes occurring naturally in a molecule are detected by presence of satellite peaks in a mass spectrum. These satellite peaks appear at values higher than that calculated from standard tables for parent or fragment ions constituted of the naturally more abundant mass. The shift in values and intensity of peaks depend on the number and natural abundance of isotopic variants in the molecule and are fixed within limits of experimental error [2,3]. When stable-labeled compounds are synthesized, the mass spectra of the parent or fragment ion show peaks shifted to m/ values equal to (M + x) depending on the nature... 

There are three expressions for mass that are important to know. The integer mass of the most abundant naturally occurring stable isotope is the nominal mass of the element. The exact mass of an isotope is determined by high-resolution MS the exact mass of Cl is 34.9689 Da and that for Cl is 36.9659 Da. The atomic weight is the... 

Table 2.3 shows the number of stable isotopes as a function of the even or odd nature of the number of nucleons. Of the 266 naturally occurring stable isotopes, more than half have an even number of both protons and neutrons. By comparison, there are only four stable isotopes having both an odd number of protons and neutrons. Furthermore, even a cursory inspection of the cosmic abundances of the elements shown in Figure 2.2 makes it clear that there are more elements having an even atomic number than there are those with an odd atomic number. In fact, there even seem to be certain magic numbers of nucleons that are consistent with the most stable nuclei. The nuclear magic numbers are analogous to the common observation... 

Manganese has a naturally occurring stable isotope, Mn, and 12 radioactive isotopes. The one of interest is Mn that has a half-Ufe of 3.7 x 10 years and decays by K-capture into the stable Cr. It may be possible to use it in assessing the terrestrial ages of meteorites and extraterrestrial dust abundances in ice and sediments. 

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