Isotopes, stable determination

Fortunately, isotopic abundances as well as isotopic masses can be determined by mass spectrometry. The situation with chlorine, which has two stable isotopes, 0-35 and 0-37, is shown in Figure 3.2. The atomic masses of the two isotopes are determined in the usual way. The relative abundances of these isotopes are proportional to the heights of the recorder peaks or, more accurately, to the areas under these peaks. For chlorine, the data obtained from the mass spectrometer are... 

Smith et al. 1996. Use of endogenous, stable lead isotopes to determine release of lead from the skeleton. Environ Health Perspect 104(l) 60-66. 

The isotope dilution gas chromatography-mass spectrometry method described by Lopez-Avila et al. [16] and discussed in section 5.3.1.3 has been applied to the determination of Atrazine in soil. In this method known amounts of labelled Atrazine were specked into soil samples before extraction with acetone-hexane. The ratio of the naturally abundant compound and the stable-labelled isotope was determined by high-resolution gas chromatography-mass spectrometry with the mass spectrometer in the selected ion monitoring mode. Detection limits of 0.1-l.Oppb were achieved. Accuracy was >86% and precision better than 8%. 

Liptay, K., J. Chanton, P. Czepiel, and B. Mosher, Use of Stable Isotopes to Determine Methane Oxidation in Landfill Cover Soils, J. Geophys. Res., 103, 8243-8250 (1998). 

In an attempt to determine whether there might be any relationship between the carbon of the anthraxolite and that of the calcite associated with it, the ratios of stable carbon isotopes were determined for each (Table IV). The results are given as C in per mil relative to National Bureau of Standards sample NBS-22 and also relative to the Urey-Chicago Standard (PDB). 

Martinelli, L A., R. L. Victoria, L. S. L Sternberg, A. Ribeiro, and M. Z. Moreira. 1996. "Using stable isotopes to determine sources of evaporated water to the atmosphere in the Amazon basin." Journal of Hydrology 183 191-204. 

Figure l6.l6 Time series of particulate nitrogen (PN) export and isotopic composition determined from 150-m floating sediment trap collections at Station ALOHA. (Top) PN flux (pmol N m d ). Error bars represent SE of three to six individual trap measurements. (Bottom) Stable nitrogen isotopic composition (c5 N) of trap-collected material (%o vs. air N2). Error bars, where shown, represent SE of two to three individual trap measurements. Dotted lines represent the isotopic compositions of exported PN expected when supported entirely hy nitrate (6.5°/oo) or entirely by dinitrogen gas (0 %o). The solid line indicates a decreasing trend determined hy linear regression. The trend break at the end of 2002 remains to he explained. Updated and revised from Dore et al. (2002). 

Liptay K., Chanton J., Czepiel P., and Mosher B. (1998) Use of stable isotopes to determine methane oxidation in landfill cover soils. J. Geophys. Res. 103, 8243-8250. 

Turk J. T., Campbell D. H., and Spahr N. E. (1993) Use of chemistry and stable sulfur isotopes to determine sources of trends in sulfate of Colorado lakes. Water Air Soil Pollut. 67, 415-431. 

Today, thermal ionization mass spectrometry is preferably used for the isotope analyses of inorganic solid samples, and electron impact instruments are preferably applied for the analyses of low-molecular gases. Therefore, Fig. 9 gives a summary of the possibilities for the isotope ratio determination in the periodic table of the elements corresponding to these two ionization methods. A position which is not marked in Fig. 9 represents an element with not more than one stable or long-lived radioactive isotope. In these cases an isotope ratio measurement by mass spectrometry is usually not possible. For the isotope ratio determination of those elements which are marked by a black bar, at least one long-lived radioactive isotope has to be used. Except uranium, these elements are only monoisotopic in nature (Be, Al, Mn, Nb, I, Cs, Bi, Th), or they are synthetic elements (Tc, Np, Pu, Am, Cm). 

We report here measurements of the stable hydrogen Isotopic composition of methane and water, the stable carbon Isotopic composition of methane and carbon dioxide, and ancillary parameters from several freshwater environments and from a few locations within the Tampa Bay estuary. The stable Isotopic compositions determined In this study are reported as a parts-per-mll ( /oo) deviation (5) from a standard with a known stable isotopic ratio. The definition of the 6 value Is ... 

Lewan MD (1983) Effects of thermal maturation on stable organic carbon isotopes as determined by hydrous pyrolysis of Woodford Shale. Geochim Cosmochim Acta 47 1471-1479 Lovelock JE, Whitfield M (1982) Lifespan of the biosphere. Nature 296 561-563... 

Mass spectrometry was originally developed to identify and analyze quantitatively the natural abundances of stable isotopes. The determination of isotopic abundances is still important today, but for different reasons. Isotopic labeling of molecules is quite important in studies of chemical mechanisms and kinetics, both in the organic and biochemical areas. Prior to studies of this kind, the extent of labeling must be determined, and mass spectrometry is usually the method of choice. For example. 

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... 

A long-standing method for thermometry has been to measure the stable oxygen isotope ratios in carbonate rocks using MS. Uranium/lead isotope ratios, determined by MS, are used to estimate the age of the earth. 

Isotope ratios, as measured by mass spectrometry, along with the known amount of the tracer, are used to determine the amount of the analyte in the sample. Isotopically altered elements (sometimes consisting of nearly pure stable isotopes) and radioactive isotopes are commercially available for use as tracers. Nearly every element can be purchased as a solution whose atom concentration is known and traceable to NIST. Standard materials are also available with isotopic composition determined to a high degree of accuracy. Radioactive tracers, such as 233U and 244Pu, are available for tracing actinide elements that do not have stable isotopes. Because many of the samples analyzed in radionuclide determinations already have altered isotopic ratios, many times it is possible to use a natural isotope as the tracer. 

Bone and teeth Stable isotope analysis Determining diet and place of origin... 

Activation analysis is another technique that has found some applications. In these methods, the desired stable isotope is made to undergo a suitable nuclear reaction. The parent isotope is determined by measurement of the resulting nuclide. As an example, the 0 content of water samples as small as 1.S jul has been determined by charged particle activation [142]. 

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