Isotope definition

Over the next few years, both the mid-infrared and the far-infrared spectra for Ar-HF and Ar-HCl were extended to numerous other bands and to other isotopic species (most importantly those containing deuterium). In 1992, Hutson [18, 39] combined all the available spectroscopic data to produce definitive potential energy surfaces that included both the angle dependence and the dependence on the HF/HCl monomer vibrational quantum number v... 

Two further expressions are used in discussions on isotope ratios. These are the atom% and the atom% excess, which are defined in Figure 48.6 and are related to abundance ratios R. It has been recommended that these definitions and some similar ones should be used routinely so as to conform with the system of international units (SI). While these proposals will almost certainly be accepted by mass spectrometrists, their adoption will still leave important data in the present format. Therefore, in this chapter, the current widely used methods for comparison of isotope ratios are fully described. The recommended Sl-compatible units such as atom% excess are introduced where necessary. 

Atomic Weight. As of this writing (ca 1994) the definition of atomic weights is based on carbon-12 [7440-44-0], the most abundant isotope of carbon, which has an atomic weight defined as exactiy 12 (21). 

Whether this is true or not, meteorites give us one definite piece of information. Isotopic analysis shows that each element in a meteorite has the same isotopes in the same percentages that this same element has on earth. The accepted explanation for this fact is that meteorites and the earth share a common origin and that they became separated after the elements were created. 

Dediazoniation does not show a significant solvent isotope effect ( h2o/ d2o = 0.98 0.01 Crossley et al., 1940 Swain et al., 1975 a). This result is definitely not consistent with a mechanism in which charge is built up on oxygen in the rate-limiting transition state, as expected for an ANDN-like process. 

As has been indicated, since there is a ring isotope effect there must be a degree of C-H bond breaking in the transition state of the rate-determining stage. Clearly further work is required in this system before a definitive mechanism can be established for the intramolecular rearrangement. 

The applicability of the linear-mixing model is seen most prominently in the interpretation of the 5 C of bone apatite which has been shown to represent the total diet, rather than being derived from energy foods , as was previously proposed by some authors. Although 5 C,p should represent total diet, the isotopic fractionation between this component and total diet appears to be somewhat variable, suggesting that more definite knowledge about this fractionation is needed if we are to use 5 C,p as an index of total dietaiy 5 C values. 

A series of papers by Merz and Riedel describe work designed to compare radiochemical behaviour following n,y n,p E.C. and p decay. Gallium isotopes are produced in most of the cases studied, but isotopes of Sn, Pb, Ge and Sb were also involved. Unfortunately, the various chromatography fractions were not well identified, so that it is not easy to draw definite conclusions from this work. Nevertheless, several things do appear to be clear. Some interesting data are presented in Table 5, comparing the effects of electron capture, neutron capture, and the (n,p) reaction. 

Cohen A, Hertz HS, Mandel J, Paule RC, Schaffer R, Sniegoski LT, Sun T, Welch MJ, and White E V (1980) Total serum cholesterol by isotope dilution mass spectrometry A candidate definitive method. Chn Chem 26 854-860. 

Ellerbe P, Cohen A, Welch MJ, and White V E (1990) Determination of serum uric acid by isotope dilution mass spectrometry as a candidate definitive method. Anal. Chem 62 2173-2177. 

Ellerbe PM, Sniegoski LT, and Welch MJ (1995) Isotope dilution mass spectrometry as a candidate definitive method for determining total glycerides and triglycerides in serum. Clin Chem 41 397-404. 

Ellerbe, P, Meiselman S, Sniegoski LT, Welch MJ, and White E V (1989) Determination of serum cholesterol by a modification of the isotope dilution mass spectrometric definitive method. Anal Chem 61 1718-1723. 

SlEKMANN L (1979) Determination of steroid hormones by the use of isotope dilution mass spectrometry a definitive method in clinical chemistry. J Steroid Biochem 11 117-123. 

Calcium exists in the human body as Ca(II) protein-bound and free Ca (II) ions (Dilana et al. 1994). For total extracellular Ca in plasma, serum and urine a definitive isotope dilution-mass spectrometry (ID-MS) method exist. Free Ca(II) in plasma/serum can be determined with PISE, but no definitive and reference methods exist. For Ca in faeces, tissue and blood flame atomic absorption (FAAS) is used widely. 

The atomic mass of an element is the weighted average mass of the isotopes of that element. Based on this definition, which of these does NOT show the correct atomic mass for an element ... 

It can be seen from Figures 3.7 and 3.8 that the calculations reproduce very well not only the experimental spectra but also the experimentally observed isotopic shifts indicating a high reliability of the computational method. According to this comparison, definite attribution can be made for even the difficult Raman bands that cannot be assigned based solely on the experimental results. It is, however, necessary to mention at this point that the calculated Raman spectrum provided directly by the ab initio computations correspond to the normal Raman spectrum with the band intensity determined by the polarizability of the correlating vibration. Since the intensity pattern exhibited by the experimentally recorded resonance Raman spectrum is due to the resonance enhancement effect of a particular chromophore, with no consideration of this effect, the calculated intensity pattern may, in many... 

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