Radioactive compounds, commercially available

In 1961/62, the considerable impurity of many of the radioactively labelled compounds commercially available at that time, was demonstrated with the help of TLC [424,... 

A modem variant is to count the number of atoms directly in a mass spectrometer.) The practical limit is about 50000 y since by this time the activity has fallen to about 0.2% of its original valuable and becomes submerged in the background counts. is also extremely valuable as a radioactive tracer for mechanistic studies using labelled compounds, and many such compounds, particularly organic ones, are commercially available (p. 310). 

In addition to the 4 stable isotopes sulfur has at least 9 radioactive isotopes, the one with the longest half-life being which decays by activity (Kmax 0.167 MeV, 87.5 d). can be prepared by Cl(n,p), S(n,> ) or S(d,p) and is commercially available as SeicmcQt H2S, SOCb and KSCN. The radiation has a similar energy to that of C ( mav 0.155 MeV) and similar counting techniques can be used (p. 276). The maximum range is 300 min in air and 0.28 mm in water, and effective shielding is provided by a perspex screen 3-10 mm thick. The preparation of many - S-containii compounds has been... 

Soil flushing is a commercially available, in situ technology for the treatment of soils contaminated with inorganic compounds including radioactive contaminants. The technology can also be used to treat volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs),... 

The use of radiolabeled nucleosides as markers for anticancer activity has become a popular method due to the commercial availability of such compounds. The technique is based upon the knowledge that cells rendered unable to replicate or killed by the anticancer agent are unable to effectively incorporate nucleic acid precursors into their DNA or RNA structure. Therefore, a decrease in cell viability correlates with a decrease in radioactivity relative to a control cell population. Although specific procedures differ, the basic technique involves the incubation of tumor cells in the presence of the radiolabeled compound with or without anticancer agent followed by scintillation counting to determine the radioacti vity of the samples. 

Chemical synthesis of labeled compounds suffers from some limitations and problems, though. One limitation concerns the amount and cost of the radioactive starting material. This factor necessitates devising synthetic routes to the desired compounds in which the radiolabel can be introduced near the end of the sequence of reactions, so as to secure as high an overall yield of labeled material as possible. At present, numerous labeled compounds are available commercially as starting materials for syntheses. Still, in planning a new synthetic route, it is necessary to consider its compatibility with the specific stalling material available. 

The main source of the alpha particles is trace quantities of uranium and thorium in the silica filler. Because silica fillers that did not contain these radioactive elements were not available, other methods for preventing alpha particles from reaching the active DRAM cells were devised. These early methods consisted of cov-vering the active cells with either a silicone or polyimide chip coat or with Rapton tape. These methods added extra steps to the manufacturing process which were cumbersome and labor intensive and, if not done precisely, had a negative reliability impact. These processes were not widely used once "low alpha fillers" became commercially available in 1982/1983. Initially, these "low alpha fillers", which contain <1 ppb uranium, were only available from one or two natural sources. Now, however, there are additional natural and synthetic sources of silica, all of which contain <1 ppb of uranium and have an alpha particle emission rate of less than. 001 alpha particles/hr-cm. Figure 9 shows where the industry was in 1980 and where it stands today. An improvement by a factor of 30-50 has been achieved with "lower alpha" filler and compound manufacturing. 

Some of these reactions can also be used for non-radioactive labelling (Isaac 1994) since Tag-polymerase, DNA polymerase I and also terminal transferase can accept compounds such as digoxygenin-dUTP (DIG-dUTP) and the dideoxy derivative DIG-ddUTP as substrates. DIG-labelled DNA can be detected colorimetrically by antibodies coupled to peroxidase using chromogenic substrates. Similar procedures can also be used to label RNA using DIG-UTP with T7- or SP6-RNA polymerases. Digoxygenin labelling kits are commercially available. 

Both the GC/ECD and GC/NICI instruments commonly analyze compounds that form negative ions such as pesticides and polychlorinated biphenyls, making devices to carry out the study of thermal electron attachment reactions commercially available. These include the radioactive and nonradioactive ECD,... 

Radioisotopes Useful in Biological Research Hundreds of biological compounds (e.g., amino acids, nucleosides, and numerous metabolic intermediates) labeled with various radioisotopes are commercially available. These preparations vary considerably in their specific activity, which is the amount of radioactivity per unit of material, measured in disintegrations per minute (dpm) per millimole. The specific activity of a labeled compound depends on the probability of decay of the radioisotope, indicated by its half-life, which is the time required for half the atoms to undergo radioactive decay. In general, the shorter the half-life of a radioisotope, the higher its specific activity (Table 3-3). 

Autoradiography is a technique for locating radioactive compounds within cells it can be conducted with light or electron microscopy. Living cells are first exposed to a radioactive precursor of some intracellular component. The labeled precursor is a compound with one or more hydrogen ( H) atoms replaced by the radioisotope tritium ( H) e.g., [ H] thymidine is a precursor of DNA, and [ H] uridine is a precursor of RNA (Chap. 3). Various tritiated amino acids are also commercially available. The precursors enter the cells and are incorporated into the appropriate macromolecules. The cells are then fixed and the samples embedded in a resin or wax and then sectioned into thin slices. 

The methods used for the detection and quantification of radionuclides and labeled compounds are determined by the type of emission (jS or y), the energy of the radiation, and the efficiency of the system by which it is measured. Commercially available instrumentation is generally used, with exception of some research work and highly specialized routine analytical application. Detection of radioactivity can be achieved in all cases with the Geiger-Miiller counter. However, for the weaker-emitting radionuclides, i.e., H, and large amounts of radionuclides are required for detection of a signal. In most cases this is both undesirable and impractical. 

A number of radioactive nuclides are commercially available. For use in organic and biochemical studies, a variety of labeled compounds are supphed. Some short-Kved tracers are supphed by generators (see Chap. 40 in Vol. 4). Detailed information is obtainable from catalogs or home pages of the companies or agencies producing or supplying radioactive nucKdes and labeled compounds. See Vol. 4 for customized synthesis of compounds labeled with H, i8p, Tc, radio-iodines, and radiometals. 

A brochure published by the International Atomic Energy Agency lists the commercially available preparations, their specific activities and the manufacturers addresses [312]. The commercially available preparations are often very impure and can be used for chemical and biochemical studies only after careful purification. The classical methods for processing crude synthetic products are generally imsatisfactory when applied to small amounts of radioactive compounds. TLC is particularly convenient for purifying radioactive compounds. A detailed account of such preparative applications of the method is given in a special section of this chapter. 

As a consequence of its radioactivity great care is required when handling the element Several promethium compounds have been prepared but very little is known about the properties of the metal itself The isotope Pm is, however, commercially available and has been tested in miniature batteries for guided missiles. The useful... 

Stable isotopes are non-radioactive atoms of the same chemical element, which differ only in their number of neutrons [19]. Many elements also have radioactive (non-stable) isotopes. The most commonly used stable isotopes in studies of macronutrient metabolism are (D or deuterium), C, and 0, while Mg, Mg, a, Ca, Ca, Fe, Fe, Zn, and °Zn are the most commonly used stable isotopes for studies of mineral metabolism. The most commonly used radioactive isotopes are and (tritium) [19]. More than 6(X)0 stable isotope-labeled compounds (tracers) are commercially available for use in metabolic studies. Examples for some of these tracers are [1- C] leucine, [1- C, N] leucine, [ring- Hj] phenylalanine, and [6,6]-D2 glucose. It is currently accepted that these compounds have neghgible biological side-effects, which renders them ethically acceptable for use in children [20]. 

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