Productivity tracer techniques

Radioactive tracer techniques. In electrochemistry, the procedure is essentially the same as in studies of chemical reactions the electroactive substance or medium (solvent, electrolyte) is labelled, the product of the electrode reaction is isolated and its activity is determined, indicating which part of the electroactive substance was incorporated into a given product or which other component of the electrolysed system participated in product formation. Measurement of the exchange current at an amalgam electrode by means of a labelled metal in the amalgam (see page 262) is based on a similar principle. 

Nonisotopic tracer techniques are also available for measurement of CH4 production. Johnson et al. [32] described a technique using SF6, an inert gas tracer. This method has been... 

The rate of dehydration of the cis diol was about fifty times slower than that of the trans diol and the product of the reaction consisted mainly of cyclohexenol. The 1,4-epoxycyclohexane formed in the reaction was formed after a prior epimerization of the cis to the trans diol this was demonstrated by means of tritium tracer technique. When irons-1,4-cyclohexanediol was dissolved in ieri-butyl alcohol-T having the hydroxyl hydrogen marked with tritium (C4H,OT) the 1,4-epoxycyclohexane produced in this reaction had a very low tritium content. A similar reaction carried out with cis-1,4-cyclohexanediol produced a highly tritiated 1,4-epoxycyclohexane. The insertion of tritium in the 1,4-epoxycyclohexane produced from the cis diol can be explained as follows ... 

Bernie Zemel is a senior research chemist in the Production Operations Research Department at Shell Development Co. He has done work in production chemistry, and on the application ol tracer techniques to ml-fieid problems. He has a BS degree from Ohio State University and a PhO from the Berate Zeaiel University of Michigan... 

Carpenter, E.3. and Livelv, 3.S., 1980. Review of estimates of algal growth using l C tracer techniques. In P.G. Falkowski (ed.), Primary Productivity in the Sea. Plenum Press, New York, pp. 166-178. 

Rowland, et al. (14) have used radiochemical tracer techniques to study reaction (1) and obtain equal yields of CO and COS. CS oxidation could account for a significant fraction of the atmospheric COS budget ( ) and definitive measurements of the mechanism of reaction (2), its primary products and the routes to, and yields of the ultimate stable products are needed. 

A tracer technique was employed in an effort to gain further information about the reaction mechanism (10). One alpha hydrogen atom of n-octyl alcohol was replaced with an atom of deuterium. The steps of the two reaction mechanisms under discussion are presented in Fig. 2. If the exchange between hydrogen and deuterium is small, the presence of significant quantities of deuterium in the gaseous product may be explained only by mechanism (1). The exact experimental details of this investigation will now be discussed. 

Fluorescent tracer techniques hold the promise of improved accuracy in assessing dermal exposures, as they require no assumptions regarding the distribution of exposure across skin surfaces. However, this approach also has several limitations. First, it requires introduction of the tracer compound into the agricultural spray mix. Secondly, there must be demonstration of a correspondence between pesticide deposition and deposition of the fluorescent compound for the production, such that the fluorescence can indeed be considered a tracer of chemical deposition. Thirdly, range-finding and quality assurance studies may be needed to ensure the accuracy of tracer measurements. Fourthly, when protective clothing is worn by workers, the relative penetration of the pesticide and tracer needs to be characterized. All of these limitations make fluorescent tracer methods technically challenging. 

The mechanism of osazone formation has been studied by the isotopic-tracer technique, by using an N -labeled arylhydrazone, treating it with an unlabeled arylhydrazone, and making an isotopic assay of the reaction products. The results were characteristic of Weygand s mechanism involving the oxidation of the hydrazone to a l-imino-lV -2-keto derivative (40) and subsequent osazone formation with the elimination of ammonia-iV . 

In 1911 Ernest Rutherford asked a student, George de Hevesy, to separate a lead impurity from a decay product of uranium, radium-D. De Hevesy did not succeed in this task (we now know that radium-D is the radioactive isotope °Pb), but this failure gave rise to the idea of using radioactive isotopes as tracers of chemical processes. With Friedrich Paneth in Vieima in 1913, de Hevesy used °Pb to measure the solubifity of lead salts—the first appfication of an isotopic tracer technique. De Hevesy went... 

At present the mechanism of complex processes may be investigated by the more precise radioactive tracer technique. The genetic relationship between individual reaction products may be determined by using this technique together with kinetic studies. The origin of reaction products and the rates of individual reactions involved in the overall process may be established by C14-labeling of the hydrocarbon molecules, or of the products suggested as intermediates. 

It may be considered on the basis of data obtained by means of the radioactive tracer technique that the various stable oxygen-containing products on semiconducting oxides are generated by different routes, through active intermediates. 

The nature of oxygen contribution to the oxidation process may be established by using the radioactive tracer technique. The reduction-oxidation mechanism of reactions is a function of the lattice oxygen mobility. Vainstein and Turovskii (86) investigated the distribution of O18 in the oxidation of carbon monoxide over MnOa and CuO and found that there will be no transfer of the catalyst oxygen to the reaction products, when water is carefully removed from the solid oxides. 

Oxidation of carboxylic acids alone and in hydrocarbon solution is accompanied by the production of C02 [204—215], Carbon dioxide is formed from the carboxylic group, as established by the tracer technique [204-210], Oxidation of R14COOH yields 14C02 [204-209] and that of RC18OOH produces C1802 [210],... 

In chemical reaction kinetics, isotope-labelled reactants are frequently employed to follow a reaction pathway and to determine the reaction mechanism (see Chapter 7.6). The isotopic tracer technique is a useful tool in catalyst surface analysis, because it enables determination of whether the adsorbed species present on the surface during the reaction are by-products or reaction intermediates. One of the adsorbed species is labelled by an isotope atom and its rate of disappearance is followed by surface spectroscopy. Simultaneously, its rate of appearance in the product molecule is followed by mass spectrometry. When both rates are identical, it can be concluded that the observed adsorbed species is the reaction intermediate. 

A more detailed study of the dehydration of 2-phenyl-1-propanol was reported and a radio tracer technique using C was used to delineate the mechanism. Of the reaction products, the allyl benzene formed was labelled only on the benzylic carbon and was thus produced by y hydrogen abstraction and concerted phenyl migration. In the a-methylstyrene, the label was equally distributed between the I and 3 carbon atoms and this product arose either through a symmetrical cyclopropane intermediate or a tertiary carbonium ion. viz-... 

Mechanistic Studies. - The application of radioactive tracer techniques to mechanistic studies in heterogeneous catalysis is, in principle, the same as their application to homogeneous reaction systems. A labelled compound, for example, a possible intermediate, is added to the reaction mixture. Gas-chromatographic separation of the reaction products and immediate radioactive assay of the separate components yields information about the chemical identity of the radioactive products and gives a quantitative measure of the degree of incorporation of the radioactive label. 

A wide range of techniques are used to determine catabolic nitrate reduction rates. These include mass balance methods using input-outputs, acetylene inhibition techniques, dinitrogen production rates, nitrate consumption rates, nitrate pore water profiles, and stable isotope tracer techniques. The limitations and advantages of these methods are discussed by Seitzinger (1988) and Herbert (1999). 

The section Radioactive Methods in volume 9 of the Treatise on Analytical Chemistry (Kolthoff and Elving 1971) discusses radioactive decay, radiation detection, tracer techniques, and activation analysis. It has a brief but informative chapter on radiochemical separations. A more recent text. Nuclear and Radiochemistry Fundamentals and Applications (Lieser 2001), discusses radioelements, decay, counting instruments, nuclear reactions, radioisotope production, and activation analysis in detail. It includes a brief chapter on the chemistry of radionuclides and a few pages on the properties of the actinides and transactinides. 

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