Radioreagent methods

In radioreagent methods, the radioactive product of the reaction between the substance to be determined and a radioactive reagent is separated by various methods, such as precipitation or liquid-liquid extraction. For example, Cl , Br or 1 in concentrations down to 0.5 pg/1 can be determined by addition of an excess of phe-nylmercury nitrate labelled with ° Hg. The complexes formed with the halide ions are extracted into benzene, whereas the phenylmercury nitrate stays in the aqueous phase. From the difference between the activities in the aqueous phase before and... 

Simple Radioreagent Methods. 141 Determination with Labeled... 

The use of radionuclide techniques in analytical chemistry was first reported in 1913 by G. Hevesy and F. Paneth in a study of the solubility of lead sulfide in water, using the natural lead isotope " Pb as indicator [67], Isotope dilution analysis was introduced by O. Hahn in 1923 [68J, using Pa to determine the yield of Pa. The development of radioreagent methods followed, and further development of radioanalytical chemistry has established a range of analytical methods and techniques ll]-[4], [61], [65], [87], [93], [95], [97]. These include the use of artificial radionuclides and labeled compounds, the principles of nuclear activation [4]-[10], [66] (- Activation Analysis), and absorption and scattering of radiation [11], [12]. The most important procedures are shown in Table 1. 

Radioanalytical indicator methods (including the radioreagent method, see Chap. 8.5) experienced a revival in the 1960s and early 1970s. Modern direct instrumental methods [19] underemphasized the importance of radioanalytical methods, which are necessary to establish the accuracy of spectroscopic methods, to avoid systematic enors. and to assess trace content in SRMs. An important advantage is the ability to reveal accidental losses, even at the ultra-trace level. 

An alternative calibration curve approach for nonquantitative reactions is to determine the distribution coefficient by a concentration-dependent distribution method [2], [75], which is a variant of the radioreagent method (Section 8.5.1). 

Radioreagent methods (RRM) are based on the use of a radioactive species in a quantitative reaction, and measurement of the change in activity of that species in the course of the reaction. The radioactive species may be a labeled reagent, the analyte, or a substance able to undergo an exchange reaction with some compound of the analyte. 

After separation from excess reagent (by liquid-liquid distribution, chromatography, precipitation. etc.), the mass or concentration of this product is determined from activity measurement. The determination is based on a radioactive substance chemically different from the analyte substance (in contrast to IDA), therefore the chemical reaction is of prime importance. By variation of this key reaction, the principle can be adapted to various procedures. The superiority of radioreagent methods over classical separation techniques arises from the use of an inactive carrier and the high sensitivity of the activity measurements, which are not subject to interference by the carrier or other substances [ 1 ], [ 16], [24], [34], [60], [87], [92], [94]. [95], [97]. 

Simple radioreagent methods (SRRM) utilize a reaction with a suitable reagent, and. sometimes with a third sub.stance one of the reagents is radioactive and the reaction is quantitative [2], [32], [87], [95]. SRRM can be classified into the following three groups ... 

Many nuclear techniques have been introduced into the field of analytical chemistry. This chapter focu on radioanalytical methods with tlie exc j on of radiotracers, used to correct for separation yield in analytical procedures, and the radioreagent technique, based on quantitative and stoichiometric reaction of an elmnent of interest. Instrumental methods such as radioactivation analysis and proton-induced X-ray emission spectrometry are also powerful nuclear analytical techniques, but they also must fall outside the scope of this short treatment. Then, the modem trends in radio-analytical methods are described, which feature autonomous analytical methods with a novel combination of chemical procedures and radioisotope techniques. 

In radiorelease methods the analyte substance A reacts with a radioactive reagent, so that radioactive R is released into a second phase, without being replaced by an inactive analyte [62], Applications involve either relea.se of radioreagents from solids or liquids into the gas phase, or release from solids into a liquid. Radiorelease methods may be classified according to the type of the radioactive reagents employed, i.e. (1) radioactive kryptonates, (2) radioactive metals, and (3) radioactive salts and other substances. 

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