Natural abundance of the Isotopes

Figrue BTl 1.1 shows the range of radiolfequencies where resonances may be expected, between 650 and 140 MHz, when Bq = 14.1 T, i.e. when the H resonance frequency is 600 MHz. There is one bar per stable isotope. Its width is the reported chemical shift range (Bl.11.5) for that isotope, and its height corresponds to the log of the sensitivity at the natural abundance of the isotope, covering about six orders of magnitude. The... 

Atoms of elements are composed of isotopes. The ratio of natural abundance of the isotopes is characteristic of an element and is important in analysis. A mass spectrometer is normally the best general instrument for measuring isotope ratios. 

Figure 9.32 illustrates the isotopic enrichment of SFe following irradiation with a pulsed CO2 laser in the 3g vibrational band, at 945 cm, of SFe, V3 being a strongly infrared active bending vibration. The natural abundances of the isotopes of sulphur are (95.0 per cent), (4.24 per cent), (0.74 per cent) and (0.017 per cent). The figure shows that depletion of SFg has been achieved to such an extent that equal quantities of SFg and SFa remain. 

Receptivity D is proportional to y NKJ + 1) where y is the magnetogyric ratio, N the natural abundance of the isotope, and / the nuclear spin quantum number Dp is the receptivity relative to that of the proton taken as 1.000. 

The natural abundances of the isotopes of four elements (Cl, Cr, Ge, and Sn) illustrate the diversity of isotopic distributions. The mass number and percent abundance of each isotope are indicated. 

Once the labeling data are available, they have to be corrected for initial biomass and natural abundance of the isotopes (see above). Next, for the part of metabolism of interest, we need to model a carbon transition network, in which... 

The molecular ion of Ci2H27SnCl is expected to produce a very complex pattern, because of the combination of the characteristic natural abundances of the isotopes of Sn, Cl and C. The theoretical calculation of the intensity pattern has taken into account all the ten isotopes of Sn, the two isotopes of Cl, three distinct contributions due to the 12 carbons (144, 145, 146), and the two significant contributions due to the 27 hydrogens (27 and 28). Of the 120 combinations, many overlap. 

Two methods of signal enhancement are particularly useful in C13 NMR experiments where signal-to-noise is rather poor owing to the low natural abundance of the isotope. Both can be performed using commercially available instrumentation although one of the methods has only recently been applied to NMR work. 

Note NMR properties of the most commonly used nuclei in in vivo NMR. The relative sensitivity derives from the physical properties of the nucleus, whereas the absolute sensitivity is the product of the relative sensitivity and the natural abundance of the isotope. 

These values are not the same as the atomic masses in the periodic table because these are the exact masses of individual isotopes.The masses in the periodic table are average masses of the element based on the masses and natural abundances of the isotopes of which it is composed. 

Table 1 lists some of the important properties of several commonly observed nuclides in the study of pharmaceuticals. Notice that some elements such as hydrogen, have several magnetically active isotopes with very different properties. Interestingly, has the highest sensitivity to detection of any nucleus, but its use is limited by the added complexity of working with a radioactive isotope. The absolute sensitivity listed in the table takes into account the natural abundance of the isotope. Sensitivity can be improved in some studies by the chemical incorporation of magnetically active isotopes such as and... 

The number of significant figures in a table of chemical or natural relative atomic masses (see the inside back cover of this book) is limited not only by the accuracy of the mass spectrometric data but also by any variability in the natural abundances of the isotopes. If lead from one mine has a relative atomic mass of 207.18 and lead from another has a mass of 207.23, there is no way a result more precise than 207.2 can be obtained. In fact, geochemists are now able to use small variations in the isotopic abundance ratio as a thermometer to deduce... 

Given the atomic masses and natural abundances of the isotopes of an element, calculate its chemical atomic mass (Section 1.4, Problems 15-18). 

In nature, 75.771 % of all chlorine atoms, by weight, are Cl-35, and 24.229% are the heavier isotope, Cl-37. The percentage distribution of the isotopes of an element is called the percent natural abundance or just natural abundance of the isotopes. All samples of chlorine, no matter the source, have the same percent natural abundance of the two isotopes. It is a nonchanging mixture of isotopes, but remember that even though they are isotopes of one another, they are still atoms of the same element and have the same chemical properties. For comparison, the isotope composition of two other elements, carbon and magnesium, are given in the following table. 

It is fortunate that P is a dipolar nucleus. However, it is frequently bonded to quadrupolar nuclei, such as N, Co, Cu, Cu, Pd, Ir, and " Au. The magnitude of complications depends on factors such as natural abundance of the isotope, quadruple moment, and the relative receptivity. 

Abundance Natural abundance of the isotope in percent. An indicates a radioactive nuclide if no value is given, the nuclide is not present in nature or its abundance is highly variable. 

Mercury (Hg) occurs in nature as a mixture of seven stable isotopes the average atomic mass of the blend is 200.6. The atomic masses and natural abundances of the isotopes are 196.0 (0.15 %), 198.0 (10.1 %), 199.0 (17 %), 200.0 (23.1 %), 201.0 (13.2 %), 202.0 (29.65 %) and 204.0 (6.8 %). Two radioactive isotopes, and ° Hg, have been widely used in toxicological studies, radiometric analysis, and also in checks of yield of analytical procedures. The fact that mercury is an isotope mixture may be of importance in analytical work using mass spectrometry, since there are no reference samples with well-defined isotope composition. 

The natural abundance of the isotopes of each element is distributed in a given ratio. Plants on the Earth first convert solar energy into biochemical energy the food chain starts from plants. Higher plants fix CO2 by the Calvin-Benson cycle to biosyntiiesize various organic compounds for their constituents. (7) It is known that the enzyme, ribulose-1, 5-diphosphate carboxylase, differentiates a small mass difference between and... 

Carbon-1.1 NMR was first siudicd in I9.S7, but its widespread use did not begin until the early 1970s. I hc reason for this delay was the lime required for ihe development of instruments sensitive enough to detect ihe weak NMR signals from Ihe C nucleus. These weak signals result frnatural abundance of the isotope (1.1%) and the small magnelogyric ratio, which is alH>ut 0.25 that of Ihe proton. I hese facttvr> combine to make C NMR about 6000 limes less sen silive than prolon NMR. 

Oxygen is the main constituent of the zeolite framework. However, NMR studies on zeolites have always been performed on isotopically enriched samples because of the low natural abundance of the isotope Timken et al. [162,163]... 

The accurate masses of the ions can be measured by means of precision mass spectrometry. For a variety of applications, it is sufficient to deal with nominal mass numbers. These are the integers close to the accurate masses. The natural abundances of the isotopes of carbon and chlorine are shown in Table 12.4. The abundances of the isotopes are given in % by mole, not in % by weight. 

A striking feature of a mass spectrum is the existence of satellite peaks. Those peaks are isotopically shifted lines that appear at masses one or more units higher than the main peak M the mass of M is calculated using the atomic masses of the most abundant isotopic species (i.e., the primary isotope). The satellite peaks, designated as M +1, M + 2, and so on, reflect the differences in the natural abundances of the isotopes. From the elemental composition of a molecular ion or fragment ion, the abundances of its satellite peaks (i.e., the isotopic pattern) can be predicted (see Example 6.1). Consider a compound of the general formula CxHj,NjO the abundance of the [M - -1] ion relative to [M] = 100% is given by... 

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