Isotopic tracer

Nuclear reaction analysis (NRA) is used to determine the concentration and depth distribution of light elements in the near sur ce (the first few lm) of solids. Because this method relies on nuclear reactions, it is insensitive to solid state matrix effects. Hence, it is easily made quantitative without reference to standard samples. NRA is isotope specific, making it ideal for isotopic tracer experiments. This characteristic also makes NRA less vulnerable than some other methods to interference effects that may overwhelm signals from low abundance elements. In addition, measurements are rapid and nondestructive. 

NRA is an effective technique for measuring depth profiles of light elements in solids. Its sensitivity and isotope-selective character make it ideal for isotopic tracer experiments. NRA is also capable of profiling hydrogen, which can be characterized by only a few other analytical techniques. Future prospects include further application of the technique in a wider range of fields, three-dimensional mapping with microbeams, and development of an easily accessible and comprehensive compilation of reaction cross sections. 

The neutron activation technique mentioned in the preceding paragraph is only one of a range of nuclear methods used in the study of solids - methods which depend on the response of atomic nuclei to radiation or to the emission of radiation by the nuclei. Radioactive isotopes ( tracers ) of course have been used in research ever since von Hevesy s pioneering measurements of diffusion (Section 4.2.2). These techniques have become a field of study in their own right and a number of physics laboratories, as for instance the Second Physical Institute at the University of Gottingen, focus on the development of such techniques. This family of techniques, as applied to the study of condensed matter, is well surveyed in a specialised text... 

Although many overall rearrangements can be formulated as a series of 1,2-shifts, both isotopic tracer studies and con utational work have demonstrated foe involvement of other species. These are bridged ions in which hydride or alkyl groups are partially bound to two other carbons. Such structures can be transition states for hydride and alkyl-group shifts, but some evidence indicates that these structures can also be intermediates. 

Fogel, M., Tuross, N. and Owsley, D.W. 1989 Nitrogen isotope tracers of human lactation in modem and archaeological populations. Annual report of the Director Geophysical Laboratory, 1988-1989. Washington, D.C., Carnegie Institution ofWashington 111-117. 

El Zorgani GA, Omer IS, Abdullah AM. 1986. Bound residues of endosulfan and carbofuran in soil and plant material. Proceedings of the Final Research Co-ordination Meeting on Isotopic Tracer-aided Studies of Unextractable or Bound Pesticide Residues in Soil, Plants, and Food. Vienna, Austria International Atomic Energy Agency, 51-56. 

Van Lieshout, M., West, C.E., and Van Breemen R.B., Isotopic tracer techniques for smdying the bioavaUability and bioefficacy of dietary carotenoids, particularly P-carotene, in humans a review. Am. J. Clin. Nutr, 77, 12, 2003. 

Isotopic Tracers in Catalysis Aromatics from / Para Ils over Te-NaX Zeolite... 

The purpose of this article is to focus on a single series of reactions and to illustrate some of these uses of isotopic tracers. The set of reactions involves the dehydrocyclization of n-paraffins into aromatics over non-acidic Te NaX zeolite (4-7). 

It also points out another advantage of isotopic tracers. The fact that a suspected intermediate reacts quantitatively to form the final product does not necessarily mean that it is an intermediate. Just because a compound is formed, or because it may give the desired final product, does not prove that the compound in question is a gas phase intermediate in the overall reaction. It must be shown that the compound behaves properly under dynamic reaction conditions, and isotopic tracers can test this behavior most effectively. 

Consequent to the work of many and employing such techniques as structure variation, isotopic tracers, and stereochemistry, a large number of different adsorbed hydro bon firagments have been identified as key intermediates in various reactions of hydrocarbons. Correlation of these spedes with similar polynuclear organometallic spedes has been of interest. However, the author feels that mechanistic understanding has lagged behind some other aspects of catalysis. 

In summary, the results from the fixed bed reactor study provided evidence as to the effect of Au and KOAc on the performance of the catalyst, though, these experiments did not give any information on the perturbation of the reaction pathways with the addition of Au and KOAc. For this type of information, additional experiments were performed using the TAP reactor with 1,2 C-labeled ethylene used as an isotopic tracer of the kinetics. 

Isotopic tracers are not exclusively radioactive. For instance, is a nonradioactive element that is suitable for a nonradioactive labeling technique. 

Henderson GM (2002b) New oceanic proxies for paleoclimate. Earth Planet Sci Lett 203 1-13 Henderson GM, Burton KW (1999) Using ( " U/ U) to assess diffusion rates of isotopic tracers in Mn cmsts. Earth Planet Sci Lett 170(3) 169-179... 

A simple case is the diffusion of a single type of ion in a solution containing a sufficient excess of an indifferent electrolyte (see page 116), which then occurs in the same way as in the case of a non-electrolyte. Isotope (tracer) diffusion has the same character, where a concentration gradient of the radioactive isotope of an ion, present in a much lower concentration, is formed in a solution with a much larger, constant salt concentration. 

Thus we shall be concerned with properties that furnish information about the nature of the ligands, the oxidation state of the metal, and the geometry of the field of ligands. Techniques such as radio-isotope tracer studies, neutron-activation analysis, and electron microscopy are powerful methods for locating a metal within constituents of the cell and are particularly suited to heavy-metal rather than organic drugs but since they do not provide information about the chemical environment of the metal they will not concern us here. After each section below we shall give an example, not necessarily from platinum chemistry, where the method has been used with success in biochemistry. 

Methane emission from ruminants can be estimated by using the ERUCT technique (Emissions from Ruminants Using a Calibrated Tracer). The tracer can either be isotopic or nonisotopic. Isotopic tracer techniques generally require simple experimental designs and relatively straightforward calculations [31]. Isotopic methods involve the use of (3H-)CH4 or (14C-)CH4 and ruminally cannulated animals. 

Unidirectional, first-order transfer rates (day1) between compartments were developed for 6 age groups, and intermediate age-specific values are obtained by linear interpolation. The range of age-specific transfer rate values are given in Table 2-8. The total transfer rate from diffusible plasma to all destinations combined is assumed to be 2,000 day"1, based on isotope tracer studies in humans receiving lead via injection or inhalation. Values for transfer rates in various tissues and tissue compartments are based on measured deposition fractions, or instantaneous fractional outflows of lead between tissue compartments (Leggett 1993). 

Rabinowitz M, Wetherill GW, Kopple JD. 1974. Studies of human lead metabolism by use of stable isotope tracers. Environ Health Perspect 7 145-153. 

Shen CD, Sun YM, Yi WX, Peng SL, Li ZA (2001) Carbon isotope tracers for the restoration of degenerated forest ecosystem. Quaternary Sciences 21 452 160 (in Chinese with English abstract)... 

The characteristics of nuclei described here are intimately related to how certain species figure prominently in chemistry (such as dating materials by determining their carbon-14 content). The use of isotopic tracers is a technique that finds applications in all areas of chemistry. 

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