Radioactive tracer method for

Applications Radiotracer measurements, which combine high sensitivity and specificity with poor spatial resolution, have been used for migration testing. For example, studies have been made on HDPE, PP and HIPS to determine effects of manufacturing conditions on migration of AOs from plastic products into a test fat [443]. Labelled antioxidant was determined radio-analytically after 10 days at 40 °C. Acosta and Sas-tre [444] have used radioactive tracer methods for the determination of styrene ethyl acrylate in a styrene ethyl acrylate copolymer. 

Radioactive Tracer Method for Detecting the Presence of Firing-Pin Supports in Fuze Assemblies (Ref 2)... 

Use of the Radioactive-Tracer Method for the Investigation of the Electric Double-Layer Structure, N. A. Balashova and V. E. Kazarinov... 

Rodina, A. G. 1957. Application of the radioactive tracer method for the solution of the food selectivity problem of aquatic animals. Zool. Zh. 36(3) 337-343 (in Russian with English sununary). 

In 1966, V. E. Kazarinov developed a new radioactive-tracer method for studying the adsorption of ions and organic substances on platinum group metals. In his studies in cooperation with O. A. Petrii, this method provided a stunning confirmation of the thermodynamic theory of platinum electrodes. Subsequently, A. Ya. Gokhshtein developed a radical new method for studying surface phenomena on solid electrodes, the so-called estance method. This method has been used in the USSR but has not so far been taken up abroad. 

The rate of adsorption of PS on to a silica surface was also studied by Pefferkom and coworkers [68, 69]. These authors used a radioactive tracer method for determining tire rate of adsorption from CCI4 on nonporous silica glass beads. They found that the rate constant decreased proportionally to the fraction of area covered... 

Durham, R.W., GR. Martin, and H.C. Sutton (1949), A radioactive tracer method for the analysis of mixtures of short-lived free radicals, Nature, 164, 1052—1053. 

Despite the advantages that sand-based systems provide for estimating rhizodeposition, studies in soil are still required. These are far more technically demanding and are heavily biased toward the use of radioactive tracer methods. 

Since the discovery of the first noble gas compound, Xe PtF (Bartlett, 1962), a number of compounds of krypton, xenon, and radon have been prepared. Xenon has been shown to have a very rich chemistry, encompassing simple fluorides, XeF2> XeF, and XeF oxides, XeO and XeO oxyf luorides, XeOF2> XeOF, and Xe02 2 perxenates perchlorates fluorosulfates and many adducts with Lewis acids and bases (Bartlett and Sladky, 1973). Krypton compounds are less stable than xenon compounds, hence only about a dozen have been prepared KrF and derivatives of KrF2> such as KrF+SbF, KrF+VF, and KrF+Ta2F11. The chemistry of radon has been studied by radioactive tracer methods, since there are no stable isotopes of this element, and it has been deduced that radon also forms a difluoride and several complex salts. In this paper, some of the methods of preparation and properties of radon compounds are described. For further information concerning the chemistry, the reader is referred to a recent review (Stein, 1983). 

Thus, if m = 10 2 mol l"1, and if all the monomer is polymerised, and if all kinetic chains are started by addition of AlX+2 to monomer, there will be 10"4 mole of Al-C bonds per base-mole of monomer. For reactions in a hydrocarbon solvent, where kp is of the order of 10s 1 mol 1 s 1, and tV2 appreciably greater, [Pn+] is correspondingly smaller and the whole task much harder. Further, before the C-Al bonds can be identified, they must be converted into a stable, analysable species by unambiguous reactions and these must be such that the products formed from the unreacted AlBr3 during the conversion do not interfere with the subsequent analysis. It is evident that radioactive tracer methods offer the best hope of solving this problem. 

Such a mechanism is not incompatible with a Haven ratio between 0.3 and 0.6 which is usually found for mineral glasses (Haven and Verkerk, 1965 Terai and Hayami, 1975 Lim and Day, 1978). The Haven ratio, that is the ratio of the tracer diffusion coefficient D determined by radioactive tracer methods to D, the diffusion coefficient obtained from conductivity via the Nernst-Einstein relationship (defined in Chapter 3) can be measured with great accuracy. The simultaneous measurement of D and D by analysis of the diffusion profile obtained under an electrical field (Kant, Kaps and Offermann, 1988) allows the Haven ratio to be determined with an accuracy better than 5%. From random walk theory of ion hopping the conductivity diffusion coefficient D = (e /isotropic medium. Hence for an indirect interstitial mechanism, the corresponding mobility is expressed by... 

A radioactive tracer method is described for the quantitative assay of HMX in mixts of HMX and RDX. The method is an isotope dilution technique in which a known amt of pure HMX, labeled with carbon-14, is added to the mixt, and the radioactivity of a fraction of... 

Several investigators have used radioactive tracer methods to determine diffusion rates. Bangham et al. (32) and Papahadjopoulos and Watkins (33) studied transport rates of radioactive Na+, K+, and Cl" from small particles or vesicles of lamellar liquid crystal to an aqueous solution in which the particles were dispersed. Liquid crystalline phases of several different phospholipids and phospholipid mixtures were used. Because of uncertainties regarding particle geometry and size distribution, diffusion coefficients could not be calculated. Information was obtained, however, showing that the transport rates of K+ and Cl" in a given liquid crystal could differ by as much as a factor of 100. Moreover, relative transport rates of K+ and Cl" were quite different for different phospholipids. The authors considered that ions had to diffuse across platelike micelles to reach the aqueous phase. 

Improvement of the techniques for monitoring local instantaneous concentrations down to the viscous dissipation microscale (e.g. spatial and time resolution of conductivity probes), development of new techniques (e.g. optical, radioactive tracer methods). 

Catalyst-circulation rate was originally measured by use of wattmeters or torquemeters connected to the bucket-elevator system (175, 185). The energy required to drive the elevator motors was calibrated against catalyst-circulation rate, as calculated from average bucket loading and number of buckets transported per hour. Later a radioactive-tracer method was developed that involves introducing a few radioactive particles into the catalyst inventory and determining the time required for each of these particles to pass from one end of the reactor seal leg to... 

Immunometric assays for TSH are available commercially as manual kit procedures or for use on automated systems. For practical reasons, nonisotopic methods dominate the market and have replaced radioactive tracer methods in most routine laboratories. The majority of immunometric TSH assays label the detection antibody with chemiluminescent labelled molecules other labels include peroxidase or alkaline phosphatase and sensitive photo-metric and fluorescenri molecules. Other assays are based on the use of fluorescent labels using europium chelates chemiluminescent compounds such as acri-dinium esters or ruthenium or bioluminescent molecules such as recombinant aequorin. ... 

Many different radioactive tracer methods have been used for estimating the unsaturated thyroid hormone binding capacity. The simplest is the T3 uptake test. Traditionally, this test is performed by measuring the distribution of radiolabeled T3 between serum binding proteins and a solid-phase binding material. In a typical assay, a diluted sample of patient serum is allowed to equilibrate with a trace amount of I-Ts and the secondary binder. A portion of the radioac-... 

Equation (50) forms the basis upon which v can be evaluated (e.g. (1) by the radioactive tracer method to evaluate simultaneously and ), (2) by comparing i values at appropriate potentials for different reactant activities (3) coupling information from high and low overpotential regions of steady-state polarization curves " (extrapolated io and charge-transfer resistance, Rcr, respectively) (4) or by back-reaction correction analysis. 2 qqie first two methods involve determination of v at any single potential while the latter two procedures must assume that the same mechanism (and hence v) applies at different potentials (at which individual measurements are required) and that the reverse reaction occurs by the same path and has the same transition state and thus rate-determining step [for both forward (cathodic) and reverse reactions]. 

There are some alternative methods for locating the dividing surface r2 can be experimentally measured at the liquid-vapor interface by using radioactive tracer methods or it may also be determined using ellipsometry so that the thickness of an adsorbed film is calculated from the ellipticity produced in light reflected from the film covered surface. On the other hand, the theoretical calculation of r2 is also possible using Monte Carlo and the molecular dynamics methods. 

Neiman (117) worked out an interesting kinetic tracer method for determining the reaction kinetics from variations in radioactivity and concentration of intermediates with time. When a substance A is converted into X, and then X is converted into B (A X -> B), then the concentration and specific radioactivity of X may be determined at any time by labeling A or X and adding the labeled substance to the reactant mixture. The rates of formation and consumption kx follow the equation... 

Experimental techniques using radioactive tracer methods are considered as being the most reliable and accurate for the determination of self or solute... 

The method is based on the international standard ISO 4053/IV. A small amount of the radioactive tracer is injected instantaneously into the flare gas flow through e.g. a valve, representing the only physical interference with the process. Radiation detectors are mounted outside the pipe and the variation of tracer concentration with time is recorded as the tracer moves with the gas stream and passes by the detectors. A control, supply and data registration unit including PC is used for on site data treatment... 

The method implies injection of a mixture of 3 radioactive tracers each being distributed into one of the 3 phases. The tracers must show such differences in the emitting y-radiation energy spectra that they can be simultaneously detected by on line y-spectrometry. Candidate tracers are Br-82 as bromobenzene for oil, Na-24 or La-140 for water, and Kr-85 for gas. The tracers are injected simultaneously at a constant rate into the flow in the pressurised pipe, and the concentration is detected as series of instantaneous measurements taken downstream as illustrated in figure 2. 

The most widely used experimental method for determining surface excess quantities at the liquid-vapor interface makes use of radioactive tracers. The solute to be studied is labeled with a radioisotope that emits weak beta radiation, such as H, C, or One places a detector close to the surface of the solution and measures the intensity of beta radiation. Since the penetration range of such beta emitters is small (a ut 30 mg/cm for C, with most of the adsorption occurring in the first two-tenths of the range), the measured radioactivity corresponds to the surface region plus only a thin layer of solution (about 0.06 mm for C and even less for H). 

Special techniques for experimentation with the actinide elements other than Th and U have been devised because of the potential health ha2ard to the experimenter and the small amounts available (15). In addition, iavestigations are frequently carried out with the substance present ia very low coaceatratioa as a radioactive tracer. Such procedures coatiaue to be used to some exteat with the heaviest actinide elements, where only a few score atoms may be available they were used ia the earHest work for all the transuranium elements. Tracer studies offer a method for obtaining knowledge of oxidation states, formation of complex ions, and the solubiHty of various compounds. These techniques are not appHcable to crystallography, metallurgy, and spectroscopic studies. 

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