Radioactive tracers, development

Concerns over safe handling of radioactive materials and issues around the cost and disposal of low level radioactive waste has stimulated the development of nonradiometric products and technologies with the aim of replacing radioactive tracers in research and medical diagnosis (25). However, for many of the appHcations described, radioactive tracer technology is expected to continue to be widely used because of its sensitivity and specificity when compared with colorimetric, fluorescent, or chemiluminescent detection methods. 

In the last case, this may be a physical problem resulting from incomplete penetration by the extraction solvent into the matrix. Alternatively, incomplete recovery of the analyte may result from chemical binding between the analyte and a constituent of the matrix. This is particularly important in the determination of drugs in body tissues where binding to proteins is known to occur. Problems of this kind are documented in the literature. If a new procedure is being developed, it is necessary to investigate the extraction step, e.g. by using radioactive tracers. 

S. Helf et al, "Development of an Inspection Method Using a Radioactive Tracer for Detecting the Firing Pin Support in PD Fuze M48A3 , PATR 2030 (June 1954)... 

The Rb-82 generator permits serial studies in the same patient as often as every 10 minutes with 20-60 mCi of Rb-82 for rapid bolus intravenous infusion. Inherent in the administration of high levels of Rb-82 activity is the need for precise flow control from an automated system to deliver the desired amount of radioactivity. The development of the alumina column parameters and the elution protocol as well as the automated microprocessor system controller are presented here. Some of the details of this system have been discussed in earlier publications (15,21). Generator produced Rb-82 is used as a diffusible flow tracer in myocardial perfusion studies and as a nondiffusible tracer in brain studies to assess blood brain barrier permeability changes in patients with brain tumors or Alzheimer s type dementia. 

A model for the tracer self-diffusivity of the interstitials is now developed for a system in which the total concentration of inert interstitials and chemically similar radioactive-tracer interstitials is constant throughout the specimen but there is a gradient in both concentrations. Since the inert and tracer interstitials are randomly intermixed in each local region,... 

Vogt et al. [9] developed Equation 6.28 from diffusion experiments using radioactive tracers between 20 and 120 meters above ground. Also the following relation holds ... 

A radioactive tracer method was developed to quantitatively measure the adsorption of high molecular wt compds on the surfaces of powdered expls. Expts were conducted by allowing a pre-weighed amt of powdered expl to equilibrate with a fixed volume of radioactive adsorbate in an appropriate solvent. The expl must be either insoluble or of very low solubility in the solvent used. At equilibrium, an aliquot of supernatant soln is removed and its radioactivity is measured. The loss in radioactivity is a measure of the amt of adsorbate taken up by the expl. By varying the concn of adsorbate in the soln, an adsorption isotherm can be constructed relating amount adsorbed with solution concn... 

The MIP-ILAs based on a direct format will be described elsewhere. ILAs based on indirect methods will be reviewed in this chapter. Like immunoassays, the first MIP-ILA, reported in 1993 by the Mosbach group [25] for the analysis of theophylline and diazepan, was based on a radioactive tracer. Since this work, many other indirect MIP-ILAs have been developed using non-isotopic tracers such as fluorophores, enzymes, or electroactive probes. 

Label selection will also affect assay sensitivity and, sometimes, selectivity. Radioactive tracers, luminescent labels, or enzymes have been applied for MIP-ILAs development and will be described in more detail in the next sections. 

An advantage of the use of radioactive tracers is that uptake and elimination of a potentially toxic substance can be studied without any perceptible increase in its concentration in the body. Also, the criticism was made that the aerosols used by Kehoe and by Griffin et al. were not identical with those produced in motor exhaust. To study uptake following inhalation of exhaust lead, a method of incorporating a tracer was developed at Harwell. 

DNA is available in human sperm and in white blood cells. From these sources, it should be possible to obtain DNA to detect changes resulting from agents, such as alkylating agents, that react chemically to cause mutations. In experimental animals, this can be done easily with radioactive tracers.238 Very sensitive and precise radioimmunoassays being developed may greatly improve quantitative assessment, so that this technique could be applied to experimental animals and man. No practical chemical assay has been developed that can be... 

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). 

This phenomenon has been studied by different combined electrochemical techniques such as -> spectroelec-trochemistry, radioactive -> tracer method, -> electrochemical quartz crystal microbalance, conductivity etc. by varying the experimental parameters, e.g., film thickness, the composition and concentration of the electrolyte solutions, the wait-time at different waiting potentials, and temperature [iii-x]. Several interpretations have been developed beside the ESCR model. The linear dependence of the anodic peak potential on the logarithm of the time of cathodic electrolysis (wait-time) -when the polymer in its reduced state is an insulator -has been interpreted by using the concept of electric percolation [ix]. Other effects have also been taken into account such as incomplete reduction [vii], slow sorp-tion/desorption of ions and solvent molecules [iii-vi], variation of the equilibrium constants of -+polarons and - bipolarons [viii], dimerization [xi], heterogeneous effects [xii], etc. 

A peeling method, in conjunction with a radioactive tracer technique, was used to obtain actual profiles of DOP concentration developed through the matrix of a PVC disc dipped into a limited volume of olive oil. The plasticiser concentration distributions were reproduced to a good approximation using a known model, adjusted by neglecting the (small) amounts of oil which diffused into the polymer. 17 refs. 

There are a number of tracers that have been used to help understand chemical reactions and interactions. Historically, development of modem tracer methods began with the pioneering work of the Hungarian physical chemist, George Charles de Hevesy, in the early 1900s. De Hevesy s work focused on the use of radioactive tracers to study chemical processes, for which he was awarded the Nobel Prize in Chemistry in 1943. Radioactive tracers, also known as radioactive labels, are based on the use of a given radioisotope. However, it is important to note that there are also isotopic tracers (or isotopic labels). Isotopes are forms of a chemical element with different atomic mass, which have nuclei with the same atomic number (i.e. number of protons) but different numbers of neutrons. Examples include H, " C, and which are radioactive forms of stable elements... 

The use of radioactive tracers in the study of reaction mechanisms has been steadily increasing over the last two decades. Tracer techniques have been used to elucidate the mechanism of complex reactions throughout the field of biotechnology and, in particular, to follow metabolic pathways, both synthetic and natural in both plants and animals. Just as the analytical problems that arose in such work educed the development of GC radioactivity detectors, so have they also evoked the development of LC radioactivity detectors. In LC, however, as the mobile phase is a liquid, radioactivity detection is more difficult and the procedures used for radioactivity detection in GC cannot be used. 

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... 

One application of radioactive tracer techniques of considerable importance in solid state structural problems is the emanation method due to Hahn (21). The method has been employed widely and has been developed recently as a sensitive, quantitative method by Gregory (22), who has employed it for the investigation of structural changes and for the extraction of diffusion data. The procedure in outline is as follows A convenient amount of a radioactive element which decays to an isotope of radon (e.g., radiothorium) is ccprecipitated... 

Other than a brief collaboration with S. AronofF, A. Benson, and M. Calvin (1947) on the distribution of label in photosynthesizing plant-tissue, this short sojourn by Hassid in the field of photosynthesis was not continued, and his involvement appears to have been based more on an interest in carbohydrate structural analysis than in the fundamentals of carbon fixation in plants. However, it is apparent from the later turn of events that this introduction to the utility of radioactive-tracer techniques for the elucidation of biochemical processes had a strong influence on his development. 

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