Radioactive Labeling Radiotracer

Amebrant and Nylander used the technique to study the sequential and competitive adsorption behavior of C-labeled jS-lactoglobulin with KT-casein on hydrophobic and hydrophilic chromium surfaces. The adsorption was also followed by in situ ellipsometry measurements, providing a basis for comparison of the two techniques as described in Section II. 1. 

Van Enckevort et al used radiochemical techniques in their studies of adsorption of BSA at the stainless steel/aqueous solution interface for a wide range of solution concentrations. It was shown that the adsorbed protein was essentially nonexchangeable and the adsorption process was not reversed upon dilution. The adsorption isotherm consisted of a plateau region that extended to the most dilute solutions studied, provided adequate time was allowed. They found adsorption from sufficiently dilute solutions to be diffusion-controlled. In ideal cases, they were able to estimate both the kinetics of diffusion-controlled adsorption and saturation coverages from molecular parameters. 

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Radiotracing is an efficient and broadly adopted method for in vivo visualization of functionalized carbon nanotubes. The radioactive labels, such as l25I,124 11 in,100,104 Cu,90 "mTc,125 and 14C,126 have made it possible to quantitatively map the location of carbon nanotubes inside animals at different doses and time points. In... 

The uptake of trace metals from the soil by plants and animals can be studied with high sensitivity by radiotracer techniques. In these applications, it is important that the chemical form of the radiotracer is identical with that of the trace element to be studied. For example, in agriculture, the uptake of trace elements necessary for plant growth can be investigated. Essential trace elements, such as Se, are of special interest. By use of radioactively labelled selenium compounds the transfer of this element from soil to plants and animals can be measured. For the investigation of the transfer of radionuclides (radioecology), addition of tracers is, in general, not needed. 

Radiochemical analysis relies on the assumption that different isotopes of the same element exhibit the same properties in any macroscopic physical or chemical process, and that radioactive labeling does not influence the other properties of a chemical species. This is generally the case, with deviations below 1% (with exception of hydrogen isotopes) owing to isotopic fractionation or radiation effects. For analytical purposes, the radiotracer and the analyte must be present in the same chemical form. This is usually easy to achieve, but specialized preparative techniques may be necessary for radioactive labeling of more complex organic compounds. 

Synthetic chemical approaches to the preparation of carbon-14 labeled materials iavolve a number of basic building blocks prepared from barium [ CJ-carbonate (2). These are carbon [ C]-dioxide [ CJ-acetjlene [U— C]-ben2ene, where U = uniformly labeled [1- and 2- C]-sodium acetate, [ C]-methyl iodide, [ C]-methanol, sodium [ C]-cyanide, and [ CJ-urea. Many compHcated radiotracers are synthesized from these materials. Some examples are [l- C]-8,ll,14-eicosatrienoic acid [3435-80-1] inoxn. [ CJ-carbon dioxide, [ting-U— C]-phenyhsothiocyanate [77590-93-3] ftom [ " CJ-acetjlene, [7- " C]-norepinephrine [18155-53-8] from [l- " C]-acetic acid, [4- " C]-cholesterol [1976-77-8] from [ " CJ-methyl iodide, [l- " C]-glucose [4005-41-8] from sodium [ " C]-cyanide, and [2- " C]-uracil [626-07-3] [27017-27-2] from [ " C]-urea. All syntheses of the basic radioactive building blocks have been described (4). 

Isotope Dilution Assay. An isotope dilution assay for biotin, based on the high affinity of avidin for the ureido group of biotin, compares the binding of radioactive biotin and nonradio active biotin with avidin. This method is sensitive to a level of 1—10 ng biotin (82—84), and the radiotracers typically used are p C]biotin (83), [3H]biotin (84,85) or an I-labeled biotin derivative (86). A variation of this approach uses I-labeled avidin (87) for the assay. 

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. 

Mineral Oil Hydraulic Fluids. Absorption of a mineral oil in an emulsion was apparently very slow in female rats injected subcutaneously with 0.1 mL and in squirrel monkeys injected intramuscularly with 0.3 mL (Bollinger 1970). The emulsion contained 1 volume mannide monoleate, 9 volumes mineral oil, and 9 volumes water [14C]labeled hexadecane, a major component of the mineral oil, was added to the emulsion as a radiotracer. At 1 week and 10 months after treatment, radioactivity remaining at the sites of injection accounted for 85-99% and 25-33%, respectively, of the administered radioactivity. 

The absorption (following administration by oral, intramuscular and intravenous routes), distribution and elimination of the drug has been studied by radiotracer techniques in rats and rabbits [283, 284]. The substituted benzoic acid was labelled with and the alkanolamine remnant with Almost all radioactivity was recovered from the urine even after oral administration. 

The chemical reactions involving positron emitters have to be specially designed to take into account the short half life of the radionuclide, the limited number of labelled precursors and the sub-micromolar amounts of these precursors. Moreover, the reactions must be possible without any addition of the stable isotope (especially when ligands of receptors are synthesized). Several practical considerations that influence the design of positron-emitter radiotracers with a high specific radioactivity and their experimental handling have been reviewed [4,8,14-19]. 

In many cases in which radiotracers are used, the chemical identity of the tracer is not important. These applications can be referred to as tracing physical processes. For example, consider those experiments that seek to locate an object in some system by labeling it with radioactivity and then measuring the position of the radioactivity in the system. Quite often a tracer that decays by y-ray emission is... 

Another interesting and important use of radiotracers in industry is in wear and corrosion studies. In studies of wear (tribology) one labels the part under study with a radionuclide. The radioactivity is concentrated on the surface undergoing wear by plating, diffusion, or ion implantation with a low-energy accelerator. The labeled part is put in service and, typically, one measures the radioactivity released in the lubricant as a measure of wear. Calibrations of the technique can be done to get absolute measures of wear. 

For small molecule analytes (see Note 6) for which a radiotracer form is available, sequentially load a known quantity of tracer dissolved in buffer and determine the amount of analyte in the eluant. When the radioactivity not retained by the immunoaffinity column plateaus, the column binding sites are saturated. Wash the column, and elute the retained radioactivity. The mass of analyte in the eluted volume is the apparent column capacity. In many instances a radio-labeled analyte may not be available. In such cases, high-performance liquid chromatography, UV spectroscopy, or any other analytical tool capable of selectively quantifying the analyte may be used to determine column capacity. 

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