Radioisotopes labeling methods

Konya, J., N. M. Nagy, and K. Szabo. 1988. The study of the ion exchange processes in system of zinc ions and calcium-bentonite, clay soil, humate and sand by radioisotopic labelling method. React. Polym. 7 203-209. 

While the radioisotopic labelling method described above has some tmquestionable advantages, the fluorescence labelling method has its outstanding features as well the sensitivity of quantitative assays is at least comparable with isotopic methods. An amount of about 10 ng of polymer tagged with one mole of fluorochrome per thousand moles of monomer units can be quantitatively determined in biological... 

Labeling. Radioisotopic labeling, one of the first labeling methods used, is stiU prominent in assays where the use of nonradioisotopic labels... 

Radioisotope-labeled nitrosamines have proven valuable in development of analytical methods and for demonstrating efficiency of recovery of nitrosamines from tobacco products and smoke (37-39). The very high specific activity required for low part-per-billion determinations has discouraged most analysts from using this approach. Unless a radiochromatographic detector with adequate sensitivity is available, samples must be counted independently of the final chromatographic determination, and one of the advantages of internal standardization, correction for variation in volume injected, is lost. 

When cells are suspended in a biological fluid or culture medium, both serum proteins and cells interact with the surface substrate. Serum protein adsorption behavior on SAMs has been examined with various analytical methods, including SPR [58-61], ellipsometry [13, 62, 63], and quartz QCM [64—66]. These methods allow in situ, highly sensitive detection of protein adsorption without any fluorescence or radioisotope labeling. SPR and QCM are compatible with SAMs that comprise alkanethiols. In our laboratory, we employed SPR to monitor protein adsorption on SAMs. 

For many years, due to the availability and low cost of radioisotope-labeled secondary antibodies, radioactive detection was the method of choice in Western blotting. Newer methods that are less hazardous and easier to use, while maintaining comparable sensitivity, have been developed. Today, Western blotting detection methods can be light-based, (chemiluminescence, bioluminescence, chemifluorescence, and fluorescence), radioactivity-based, or color-based. It is important to note that the detection sensitivity depends on the affinity of the primary antibody for the antigen and on the affinity of the secondary antibody for the primary antibody and can therefore vary considerably from one protein sample to another and from one antibody batch to another. 

Immunochemical methods that utilize radioisotopic labeling can detect the use of anabolic sex hormones that increase the growth in meat animals. Stilbene [588-59-0], C14H12, trenbolone [10161-33-8], and zeranol [55331-29-8], C18H2605, can be successfully monitored by these immunoassay techniques (45). In order to prevent veterinary dmgs from being transported to the human food chain, radioisotopic immunoassays were developed to monitor veterinary antibiotics such as penicillin and chloramphenicol [56-75-7], C H CyX C, in meat, milk, and eggs (qv) (see Antibiotics Meat products Milk AND MILKPRODUCTS). 

For the membrane array of cytokine expression, the general procedures (Amersham Pharmacia Biotech R D Systems SuperArray Inc., Bethesda, MD Clontech Laboratories, Inc., Palo Alto, CA) include RNA extraction, reverse transcription into biotin- or radioisotope-labeled cDNA, hybridization with about 20 to several hundred different cDNA prespotted membranes, and signal detection using fluorescence or radioactive methods (L3). As an example, Fig. 4 and Table 4 show different chemokine genes upregulated in allergic asthmatic patients compared with normal controls, based on membrane array technology (SuperArray). 

What may prove to be the ultimate choice for an internal standard when using an MS (37) is the addition of a PGS standard as a deuterated compound to the initial sample preparation. The deuterated compound is quantified directly on the MS rather than having to subsequently subject the sample to conventional radioisotope detection methods. This procedure has been applied to ABA (29) and IAA (38, 39) analyses. A high deuterium content (labeled at five or more positions) should be sought to avoid confusion with naturally "heavy" isotopic compounds (39). 

There are two principal methods for determining the susceptibility of skin to penetration by toxicants. The first of these is measurement of the dose of the substance received by the organism using chemical analysis, radiochemical analysis of radioisotope-labeled substances, or observation of clinical symptoms. Secondly, the amount of substance remaining at the site of administration may be measured. This latter approach requires control of nonabsorptive losses of the substance, such as those that occur by evaporation. 

Chemical modification is now a senior technique in protein science and has retained its importance despite the introduction of many powerful modern physical methods over the last 30 years. Some of the more useful areas of chemical modification have been reactive or active-site modifications, modifications to alter physical and biological properties, radioisotopic labeling, and modifications for analytical purposes. 

The most representative method for the analysis of DNA hybridization is southern blotting in which separated DNA fragments are blotted onto a nitrocellulose physical support and radioisotopically labeled DNA probes are annealed to the complementary targets. It has good sensitivity and selectivity, however, this method requires a large amount of radioisotopic labeling. 

The basic information in the study of sorption processes is the quantity of substances on the interfaces. In order to measure the sorbed quantity accurately, very sensitive analytical methods have to be applied because the typical amount of particles (atoms, ions, and molecules) on the interfaces is about I0-5 mol/m2. In the case of monolayer sorption, the sorbed quantity is within this range. As the sorbed quantity is defined as the difference between quantities of a given substance in the solution and/or in the solid before and after sorption processes (surface excess concentration, Chapter 1, Section 1.3.1), all methods suitable for the analysis of solid and liquid phases can be applied here, too. These methods have been discussed in Sections 4.1 and 4.2. In addition, radioisotopic tracer method can also be applied for the accurate measurement of the sorbed quantities. On the basis of the radiation properties of the available isotopes, gamma and beta spectroscopy can be used as an analytical method. Alpha spectroscopy may also be used, if needed however, it necessitates more complicated techniques and sample preparation due to the significant absorption of alpha radiation. The sensitivity of radioisotopic labeling depends on the half-life of the isotopes. With isotopes having medium half-time (days-years), 10 14-10-10 mol can be measured easily. 

Catecholamines. The quantitative determination of dopamine and noradrenaline in tissue samples of 0.1-10 mg at levels in the order of 0.5 pmol has been described [84]. These methods are based on extraction, formation of the pentafluorpropionyl derivatives, and the use of the homologues, a-methyidopamine and a-methylnoradrenaline as internal standards in SIM. Higher sensitivity than obtainable with fluorimetric or enzymic assays is reported [462J. Applications have been to amine determination in specific regions of rat brain [84] and to measurement of heart ventricle concentrations [463]. A combination of assays of this type with the use of synthesis inhibitors or radioisotope labelled precursors allows direct estimation of brain amine turnover in animals. 

While no real labels meet all of these needs, the properties of some of the more recently introduced labelling systems are approaching the ideal. Radioisotopes, once the only type of label used for immunoassays, have clearly been overwhelmed by current applications of fluorescent labeling methods, enzyme labels, and even coenzyme and prosthetic group labels. A variety of alternative labels has also been investigated, including red blood cells, latex particles, viruses, metals, and free radicals. Table 6.1 shows a representative listing of labels used in modem immunoassays.1... 

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