Detection radioactivity

Urinary excretion of radioactivity was measured in human volunteers during and after a 3.5-hour period of dermal exposure to 0.11 or 0.22 g 32P-labeled TOCP (Hodge and Sterner 1943). The specific activity of the test substance was not reported. Radioactivity in urine was measured with a Geiger-Muller counter, but the limits of detection were not reported. Maximum estimated excretion rates, 10 and 43 pg TOCP/hour for the respective dosage levels, were measured within 24 hours of initiation of exposure. Radioactivity was not detected 48 or 72 hours after dosing ceased. Cumulative radioactivity detected in urine accounted for 0.13% and 0.36% of the dermally applied radioactivity. 

Distribution. Cyanide is rapidly distributed by the blood throughout the body. In a study using orally administered radioactively labelled potassium cyanide, radioactivity detected in whole blood or plasma decreased rapidly within 6 hours. Of the low levels of radioactivity detected in the red blood cells, about 94% of the radioactivity recovered was found in the hemolysate of which 70% was detected in the heme fraction, 14-25% in globin, and only 5-10% in cell membranes (Farooqui and Ahmed 1982). Yamamoto et al. (1982) determined that the pattern of distribution of cyanide did not vary with the concentration used. Ballantyne (1983b) observed higher cyanide levels in whole blood than in serum in rabbits exposed dermally to hydrogen cyanide, potassium cyanide, and sodium cyanide. See Section 2.3.2.1 for specific studies on cyanide tissue distribution. 

This was the first extinct radioactivity detected (Jeffrey and Reynolds 1961) and was made possible by the early high sensitivity of rare gas measurements and the low abrmdance of Xe in rocks. I has only one stable isotope at mass 127. Its abundance is measured as Xe after exposing a sample to an adequate neutron flux. The correlation between Xe and Xe observed in a stepwise degassing of a sample demonstrates that the excess Xe results from decay (Fig. 9h). Results in primitive meteorites and inclusions show that i29j/i2tj j.jose to 10 . Chronometry with I- Xe has been widely used in meteorite work (Reynolds 1963 Hohenberg 1967) but occasionally has some diflflculties to agree with the other chronometers due to the sensitivity of I to secondary processes and water alteration (Pravdivtseva et al. 2003 Busfleld et al. 2004 see also Swindle and Podosek (1988) for an extensive review). ... 

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. 

Three types of detection methods can be used for in situ hybridization radioactive, fluorescent, and chromogenic. Radioactive detection techniques are the most commonly used primarily because they are more sensitive, but also because the other techniques are relatively more recent in terms of the development of the appropriate chemistry and the techniques that enable in vitro labeling of probes by these nonradioactive means. 

Fig. 7. Droplet charge and levitation voltage for radioactivity detection in a C-con-taminated electrodynamic balance, from Davis et al. (1988).

Fig. 1.38 LC separation with radioactivity detection of an urine sample. The response of the various peaks is directly proportional to the amount of metabolites present in the sample. Peaks HU1-HU3 human urine metabolites.

Careful preliminary tests were necessary to demonstrate the suitability of these methods for the present study. In particular, it was necessary to verify that the radioactivity detectable in the polymer may not be caused by contamination or other processes different from the ones taken into consideration. It was then found that it is possible to remove throughly from the polymer the last traces of unreacted ethylaluminum or of its soluble complexes with titanium compounds by washing with anhydrous hydrocarbon. No alkylation of the preformed polymer caused by triethylalu-minum or its derivatives has been observed (4 ). 

Chromatographic analysis of the incurred livers showed how many metabolites were present in the analyzed extracts. It was found that only 7% of tire radioactivity detected in liver and 70% of that in fat were due to the presence of the parent monensin. The rapid metabolism and depletion of the unchanged monensin were attributed to (9-demetlrylation and oxidation at various positions along the carbon backbone of its molecule. 

Presently, nonradioactive probes, especially biotin or digoxigenin, are favored because they are less hazardous to work with, can be more rapidly developed, and provide better spatial resolution. Thus, introduction of nonradioactive detection systems has made ISH, using formalin-fixed and paraffin-embedded tissues, more accessible for application to molecular cell biology and diagnostic pathology. However, radioactive detection systems are more sensitive than nonradioactive probes, especially oligonucleotide probes used instead of cRNA probes (Sperry et al., 1996). 

Applications of High-Sensitivity Mass Spectrometry and Radioactivity Detection Techniques in Drug Metabolism Studies... 

Kiffe, M., Jehle, A., and Ruembeli, R. (2003). Combination of high-performance liquid chromatography and microplate scintillation counting for crop and animal metabolism studies A comparison with classical on-line and thin-layer chromatography radioactivity detection. Anal. Chem. 75 723-730. 

Figure 5. Translocation of radioactivity in spring barley after testing the upper side of the lower half of the leaf with [ C]triadimefon (macroautoradiographic radioactivity detection). (Reproduced with permission from Ref. 19. Copyright 1978 Pflanzenschutz-Nachrichten Bayer.)...

Chemiluminescence is a very sensitive and selective technique. Reagent types, analytes, and detection limits have been summarized in a review by Imai.56 Chemiluminescence has been applied to the analysis of compounds that exhibit low UV absorbance, including metal ions, amino acids, fatty acids, and bile acids. Other detectors include detectors for radioactivity, nuclear magnetic resonance (NMR), and surface-enhanced Raman spectroscopy. Radioactivity detection is one of the most selective detectors, as only components that have been radiolabeled will be detected. The interface of NMR with HPLC and has been discussed in detail by Grenier-Loustalot et al.57 Surface-enhanced Raman spectroscopy is another technique that... 

The availability of an on-line radioisotope detector for CE is especially appealing for several reasons. First, state-of-the-art radiation detection technology offers extremely high sensitivity. Second, radioisotope detection affords unrivaled selectivity because only radiolabeled sample components yield a response at the detector. Third, the radiolabeled molecule possesses the same chemical properties as the un-labeled molecule, thereby permitting tracer studies. Fourth, radioisotope detection can be directly calibrated to provide a measurement of absolute concentration of the labeled species. Finally, a capillary electrophoresis system in which radioactivity detection is coupled with more conventional detectors adds extra versatility to this new separation technique. 

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