Isotopic concentration

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

The efficiency of a helium—neon laser is improved by substituting helium-3 for helium-4, and its maximum gain curve can be shifted by varying the neon isotopic concentrations (4). More than 80 wavelengths have been reported for pulsed lasers and 24 for continuous-wave lasers using argon, krypton, and xenon lasing media (111) (see Lasers). 

Thorium isotope concentrations and ratios, as well as parent and daughter isotope concentrations, are used to date and study the formation and metamorphosis of rocks and sediments. For example, has been used to date coral reef terraces (4). / Th disequiUbria and Th/ Th... 

Isotopic Concentration. A number of techniques have been reported for concentrating tritium from naturally occurring sources. For example, separation factors (H/T) of 6.6 to 29 were observed (49) for the concentration of tritium by electrolysis of tritiated water. Tritium is concentrated in the undecomposed water. 

Direct measurements of 180/160 in rain and snow have been made and are available in publications of the International Atomic Energy Agency [17] figure 7 shows the 180 and D correlations with temperature for Austrian stations for the past 15 years. The isotope concentration of precipitation varies similarly with temperature in many other places as shown by plots of the IAEA isotope measurements against air temperature. 

This problem, in which a radiogenic element is allowed to leak out of its host mineral as it forms, has found important applications in geochronology, particularly for the K-Ar method (Wasserburg, 1954) and the U-Pb method (Tilton, 1960 Wasserburg, 1963) with the so-called continuous loss model. The equation for radial diffusion of a radiogenic element in a sphere with radius a and uniform parent isotope concentration P = P0 at t = 0 can be written... 

Many rate constants in aqueous solutions are pH or pD sensitive. In particular, enzyme catalyzed reactions often show maxima in plots of pH(pD) vs. rate. The example in Fig. 11.5 is constructed for a reaction with a true isotope effect, kH/kD = 2, and with maxima in the pH(pD)/rate dependences as shown by the bell shaped curves. These behaviors are typical for enzyme catalyzed reactions. When the isotope effect is obtained (incorrectly) by comparing rates at equal pH and pD, the values plotted along the steep dashed curve result. If, however, the rate constants at corresponding pH and pD (pD = pH + 0.5) are employed, a constant and correct value is obtained, kH/kD = 2. Thus for accurate measurements of the isotope effects one must control pH and pD at appropriate values (pD = pH + 0.5 in our example) using a series of buffers. In proton inventory experiments (see below) buffers should be employed to insure equivalent acidities across the entire range of solvent isotope concentration (0 < xD < 1), xD is the atom fraction of deuterium [D]/([H] + [D]). 

Many salt minerals have water of crystallization in their crystal structnre. Such water of hydration can provide information on the isotope compositions and/or temperatures of brines from which the minerals were deposited. To interpret snch isotope data, it is necessary to know the fractionation factors between the hydration water and the solntion from which they are deposited. Several experimental studies have been made to determine these fractionation factors (Matsno et al. 1972 Mat-subaya and Sakai 1973 Stewart 1974 Horita 1989). Becanse most saline minerals equilibrate only with highly saline solutions, the isotopic activity and isotopic concentration ratio of water in the solntion are not the same (Sofer and Gat 1972). Most studies determined the isotopic concentration ratios of the sonrce solntion and as Horita (1989) demonstrated, these fractionation factors have to be corrected using the salt effect coefficients when applied to natural settings (Table 3.2). 

Thorium Isotopic Concentration in Three Occupational Cases and the General Population... 

TABLE 5-3. Thorium Isotopic Concentration In Three Occupational Cases and the General Population of Grand Junction, Colorado (pCI/kg)... 

Equation 5.18 offers a convenient technique for measuring self-diffusion coefficients. A thin layer of radioactive isotope deposited on the surface of a flat specimen serves as an instantaneous planar source. After the specimen is diffusion annealed, the isotope concentration profile is determined. With these data, Eq. 5.18 can be written... 

Fig. 51. Models of H2-D2 reactions for H3PMoi204o (right) and H3PW 204o (left). Values are given in units of 10 6 mol min"1 g Outer circle indicates the surface of H3PMoi2040 and H3PWl2O40 p and b, respectively, indicate bulk phase and hypothetical portion in which the isotopic concentration is uniform. (From Ref. 262.)...

Kim, C. S., Kim, C. K., Martin, P., and Sansone, U., Determination of Pu isotope concentrations and isotope ratio by inductively coupled plasma mass spectrometry A review of analytical methodology, J. Anal. At. Spectrom., 22, 827-841, 2007. 

Due to the distinctive mass spectral patterns caused by the presence of chlorine and bromine in a molecule, interpretation of a mass spectrum can be much easier if the results of the relative isotopic concentrations are known. The following table provides peak intensities (relative to the molecular ion (M+) at an intensity normalized to 100%) for various combinations of chlorine and bromine atoms, assuming the absence of all other elements except carbon and hydrogen.1 The mass abundance calculations were based on the most recent atomic mass data.1... 

Due to the inability to reliably detect beet sugar additions, the site-specific natural isotope fractionation nuclear magnetic resonance (SNIF-NMR) method used widely in the wine industry was adapted for the maple industry (Martin et al., 1996). This method determines the site specific isotope concentrations of organic compounds by nuclear magnetic resonance of ethanol fermented from the suspect sample. 

Plasma source mass spectrometry has also been used in the identification and differentiation of trace metals between anthropogenic and natural sources using an isotopic technique. Although, in the past, isotopic studies were mainly concentrated on Pb (206Pb, 207Pb and 208Pb) (Ault et al., 1970 Callender and Rice, 2000 Hansmann and Koppel, 2000 Semlali et al, 2001, 2004), modem techniques now also enable the characterisation of Cu and Zn isotopic concentrations in soils (Archer and Vance, 2004). 

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