Activation analysis stable tracers

Short reviews appeared on the various MS techniques for quantitation of stable isotopes and long-lived radioisotopes and the application of Mg stable isotopes as tracers in biology and medicine. The radioactive isotope Mg is not usually available and has a short half-life (21.3 h), hence its hmited usefulness as a tracer. The sensitivities and interference problems encountered in activation analysis for Al, Mg, Mo, P, Si and Zr were discussed. Much higher sensitivities were found for cyclotron-produced than for reactor-produced fast neutrons or 14 MeV neutrons. ... 

For the following analyses, indicate whether radiochemical neutron activation analysis would be preferred to instrumental neutron activation analysis. If radiochemistry is indicated, briefly sketch the separation procedures to be used (a) the determination of ppm levels of Mo in flathead minnows, (b) the determination of the trace-element content of agricultural field-burning particulate matter, (c) the use of stable activable tracers to determine flow patterns in an ocean estuary, and (d) the determination of Dy in pine needles. 

Guinn, V, P, Activation Analysis with Particular Attention to the Detection of Stable Tracers. In Isotopes in Experimental Pharmacology (L.J. Roth, Ed.). Chicago University of Chicago Press 1965. 

Direct measurement of dietary zinc availability in humans requires development of the stable isotope tracer methodology. Several aspects of this integrated methodology are considered and briefly discussed. These are analytical isotopic measurement methodology, consequences of the finite precision of isotopic measurements, validation of in vivo measurements, and several aspects of biological labeling of human foods. It is shown that Radiochemical Neutron Activation Analysis provides a suitable method for accurate measurement of the stable isotopes Zn,... 

Two methods that have been used in tracer studies with are neutron activation analysis CNAA) and EIMS, mass spectrometry of a volatile chelate with electron impact ionization C15>19,20). Neither technique can match TIMS in accuracy or precision, but both may offer greater sample throughput. Until more precise techniques become more generally available, research utilizing stable metal isotopes will remain limited to the conditions imposed by the analytical facilities at hand. As will be shown below, research with stable magnesium isotopes to date, has had to be tailored to the limitations of available analytical techniques ... 

Stable Isotope Techniques. Although the availability of radioiron isotopes has facilitated our understanding of iron nutrition, their utilization is becoming restricted for safety and ethical reasons, especially when infants, children, and women are involved. The availability of enriched stable iron isotopes (Table I) and methodologies for quantifying them make stable isotopes a feasible alternative to radioisotopes as biological tracers. Neutron activation analysis and mass spectrometry are currently available to nutritionists for quantifying stable isotopes of minerals. 

A stable activable tracer (SAT) is a stable material that is injected into a system under study and whose concentration in the system is measured by a post sampling activation analysis. The advantages of such "artificiar tracers as compared with the naturally occurring trace elements in various systems (which act as natural tracers) are as follows artificial tracers have a controlled emission rate (either pulse or continuous injection) and control of the amoimt injected, both of which are valuable in model validation studies they can be injected in amounts suflBcient to ensure easy detection in the system under study and they lend themselves better to simultaneous tracing of several similar pollutant sources. 

Choice of SATs. What elements should one choose as stable activ-able tracers Probably no universal tracer suitable for all applications exists, but certain general criteria can be stated for the choice of suitable SATs. These criteria include a good detection sensitivity (which for neutron activation analysis translates into a high neutron capture cross section and/or a short half-life for the activation product) a reasonable cost (as measured by the sum of analysis and tracer cost) a low natural concentration the fact that it is nonhazardous at environmentally useful concentrations and an equivalence in behavior to the material being traced. 

One of the most appropriate uses of stable activable tracers is in measuring removal of pollutants from the atmosphere. The concentrations of species are extremely low even in tracer experiments (/ ng/L), and the good detection sensitivity of activation analysis is a necessity along with the controlled emission of the tracer. Much of this work has been carried out by the Battelle Pacific Northwest Laboratories and is summarized in annual reports of that laboratory from 1972-1976. 

Applications of Stable Tracers and Activation Analysis in Plant and... 

In recent years life science researchers have become more earnest in their considerations that trace elements have important roles in physiology and pathology. So far, some of these experimenters have used activation analysis (1) to measure the elemental contents of biological tissues and fluids (2) to determine if a correlation exists between abnormal trace element concentration and certain types of diseases (3) as an investigational method for epidemiological functions (4) to measure metabolic functions (5) as a clinical and investigational method for toxicology (6) in total body in vivo studies (7) in in vivo studies with stable tracers and (8) in individual identifications for forensic requirements. 

In addition to these reports, other researchers have studied metabolic functions with stable isotopic tracers and activation analysis. Examples of these applications are given in part G of Section IV. 

Generally, determination of stable isotopes is more complicated than radioactivity counting. Activation analysis is useful for isotopic tracer technique. In this method, radioactive isotope is not added to the sample but produced in it by irradiation. The common used nuclear reaction is the (n,y) reaction that is brought about by thermal neutrons. After the radioactive isotopes are produced, they can be determined simply by virtue of their irradiations. In addition, traditional methods for analysis of isotope ratios include... 

Analysis of the isotope distribution in target compounds can be, and frequently been, limited to measuring bulk specific activity (in the case of radioisotopes) or the overall abundance (in the case of stable isotopes) of the tracer isotope. Alternatively, the topological distribution of the isotope label can be narrowed down by chemical degradation in the case of radioactive tracers. In case of stable isotopes, the topology of isotope distribution in the target molecule can be assessed in considerable detail by NMR spectrometry, mass spectrometry, or a combination of these methods. 

Dispersal, Collection, and Analysis of the Tracer. The dispersal of the stable activable tracer is similar to that of a chemical tracer, radiotracer, etc. Tracer aerosols can be produced by, for example, p)n otechnic flares, acetone burners, or spraying water solutions. Dispersal in water should cause little problems other than concern that the initial tracer concentration near the point(s) of dispersal may be high. Collection and analysis of the tracer species proceed like the analysis of the trace element content of any matrix, except that the tracer should be present at a level high enou to ensure easy detection. 

Use of a radioactive tracer to determine a chemical yield is part of a broad suite of techniques known as isotope dilution The analyst wishes to measure the amount of a stable element X in a sample from which a pure chemical fraction of X can be only incompletely separated. A tracer aliquot containing a known mass of X (Mx), labeled with a radioactive isotope of X characterized by radioactivity of a known intensity (C), is added to the sample. A separation is performed to obtain a pure sample of X of mass Ms and a measured radioactive intensity of C which is less than C due to losses in the separation procedure Ms is determined by any suitable standard quantitative-analysis method (e.g., gravimetry of a stoichiometric compound of X). The specific activity of the chemical fraction, C /Ms, is equal to the specific activity of the element X in the mixture after tracing but prior to... 

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