Radiochemical analysis methods

Uranium in nature may be measured either radiometrically or chemically because the main isotope - 238U - has a very long half life (i.e., relatively few of its radioactive atoms decay in a year). Its isotopes in water and urine samples usually are at low concentrations, for which popular analytical methods are (1) radiochemical purification plus alpha-particle spectral analysis, (2) neutron activation analysis, (3) fluorimetry, and (4) mass spectrometry. The radiochemical analysis method is similar in principle to that of the measurement of plutonium isotopes in water samples (Experiments 15 and 16). Mass spectrometric measurement involves ionization of the individual atoms of the uranium analyte, separation of the ions by isotopic mass, and measurement of the number of separated isotopic ions (see Chapter 17 of Radioanalytical Chemistry text). 

Assessment and judgement of the 15 more unusual radionuclides, associated waste streams and related uncertainties was used to prioritise the benefit of development of new chemical/radiochemical analysis methods as compared to further theoretical calculations. 

Although there are many radioactivity detectors available, there has been very little development of analytical instruments or radiochemical sensors suitable for rapid and selective quantification of beta- and alpha-emitting radionuclides such as c, Sr, and TRU actinides in water or process streams. Current baseline analytical methods for these analytes are based on tedious manual radiochemical analysis methods performed in centralized laboratories. 

These developments represent significant success in the development of radiochemical analysis methods for at site or in situ radiochemical measurements that can provide timely information on radiological conqrosition in environmental or process monitoring applications. 

A slightly different example is the separate determination of rates of reaction of nC and 14C labeled methyl iodide with N,N-dimcthyl-/>-toluidine as illustrated in Fig. 7.3. Again the method takes advantage of the convenience of radiochemical analysis. If, as likely, the KIE of interest is ki2/ki4, it can be obtained to sufficiently good approximation by applying a modified Swain-Schaad rule, ln[ki2/ki4]/ln[kn/ki4] = [(12/14)/(11/14)]1/2 obtained from the law of the geometric mean (see Section 10.5). 

Procedures for the determination of 11 elements in coal—Sb, As, Br, Cd, Cs, Ga, Hg, Rb, Se, U, and Zn—by neutron activation analysis with radiochemical separation are summarized. Separation techniques include direct combustion, distillation, precipitation, ion exchange, and solvent extraction. The evaluation of the radiochemical neutron activation analysis for the determination of mercury in coal used by the Bureau of Mines in its mercury round-robin program is discussed. Neutron activation analysis has played an important role in recent programs to evaluate and test analysis methods and to develop standards for trace elements in coal carried out by the National Bureau of Standards and the Environmental Protection Agency. 

This article presents a comprehensive view of the present state-of-the-art of radiochemical separations for the following trace elements in coal Hg, Rb, Cs, Se, Ga, As, Sb, Br, Zn, Cd, and U. Most of the work on the determination of trace elements in coal is very recent. The accuracy of the analysis methods, nearly all newly developed, has been open to question because of the lack of standards and lack of knowledge of the range of concentrations for many trace elements in coal. Federal government laboratories have taken the lead in evaluating methods of analysis and in developing standards. By a round-... 

Since not many natural radioactive elements are in existence analysis by radiochemical methods was rather limited until it became possible to "induce radioactivity artificially in some of the non-radioactive elements, as was first done in 1934 by I. Curie F.Joliot(Ref 1). This discovery greatly broadened the application of radiochemical analysis. The first application of artificial radio activation for the identification of constituents in a mixt was reported by Meinke (Ref 16) to have been done in 1936 by Hevesy 8t Levi (Ref 2). 

Monk, R. G., and K. C. Steed Microchemical Methods in Radiochemical Analysis. VI. Determination of Chemical Yields by Micro-Coulometry. Anal. Chim. Acta 26, 305 (1962). 

Laboratory robotics represents an attractive approach for the automation of sample preparation and separation steps in radiochemical analysis, and for many years, such methods have been routinely used by laboratories serving the analytical needs of the International Atomic Energy Association.64 68-72 However, there are currently a limited number of published studies containing technical details on the radiochemical separations and how they were automated. Accordingly, the remainder of this chapter will focus on fluidic approaches. 

Although best known for simple serial assays in homogeneous solution, such as colorimetric reactions, FI methods have also been developed that perform separations or utilize solid phases.33 34,42 73 -76 The use of solid-phase separation columns in FI or SI systems for radiochemical analysis gathered momentum in the 1990s. 

By the late 1990s and into the 2000s, a number of additional groups became involved in automated fluidic separations for radiochemical analysis, especially as a front end for ICP-MS. Published journal articles on fluidic separations for radio-metric or mass spectrometric detection are summarized in Tables 9.1 through 9.5. The majority of such studies have used extraction chromatographic separations, and these will be the main focus of the remainder of this chapter. Section 9.4 describes methods that combine separation and detection. Section 9.5 describes a fully automated system that combines sample preparation, separation, and detection. 

Conventional radiochemical analysis of nuclear process or waste samples in the laboratory entails three primary activities sample preparation, radiochemical separation, and detection. Each of these activities may entail multiple steps. The automated fluidic methods described above, typically also carried out in the laboratory, link separation and detection. Sample preparation has, in many cases, been carried out first by manual laboratory methods. 

Experimentally, the investigation of adsorption from solution is much simpler than that of gas adsorption. A known mass of adsorbent solid is shaken with a known volume of solution at a given temperature until there is no further change in the concentration of the supernatant solution. This concentration can be determined by a variety of methods involving chemical or radiochemical analysis, colorimetry, refractive index, etc. The experimental data are usually expressed in terms of an apparent adsorption isotherm in which the amount of solute adsorbed at a given temperature per unit mass of adsorbent - as calculated from the decrease (or increase) of solution concentration - is plotted against the equilibrium concentration. 

The radioanalytical methods of determining 55Fe and 63Ni were worked out by Holm et al.6 and Skwarzec et al.11 Figures 11.1 and 11.2 illustrate the procedures for the radiochemical analysis of 55Fe and 63Ni in aquatic environmental samples. 

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. 

This laboratory experiment describes the preparation of a vegetation sample (e.g., grass) for radiochemical analysis. The sample is dried and ashed. In Part 12A, the ash is fused with sodium hydroxide and sodium carbonate to bring it into solution. An alternative method in Part 12B uses a microwave-assisted digestion technique with nitric and hydrofluoric acid. The prepared sample is suitable for radionuclide analysis, notably for radio-strontium or plutonium. 

Proper preparation of biological solids for radiochemical analysis is essential for obtaining valid radioanalytical chemistry results. The samples often must be large because the radioactivity levels are low. Gamma-ray spectral analysis is the preferred method of radiation measurement because it requires little preparation. If gamma-ray spectral analysis of the untreated sample is not feasible because few or no gamma rays are emitted, the sample must be dissolved. Dissolution is almost always required for alpha- and beta-particle analysis. The first step usually reduces the mass of the solid sample and prepares it for dissolution. 

The plasma of a dog intravenously administered solutions of l c-A -tetrahydrocannabinol was monitored with time after heptane extraction by both radiochemical analysis and electron-capture GLC of the derivative of the appropriately collected eluate fraction from normal phase HPLC. Typical plots of the time course of the results from both methods are given in Figure 7. 

The procedure for GLC analysis gave a lower limit for quantitation of 1 in plasma of approximately 1 ng/ml from twice the standard deviation (0.32 ng) obtained for the amount of 1 recovered from 2.25 ng in 2 ml of plasma. Similarly, the procedure for radiochemical analysis gave a lower limit of approximately 0.2 ng/ml from twice the standard deviation (0.084 ng). A statistical analysis of the apparent differences between the tetrahydrocannabinol assays at a given time from both analytical methods showed no significance. 

Although the yield of the separation Is extremely low, l.e., estimated as 6.88 x 10 In the separation of Zr, method is useful as a good qualitative radiochemical analysis technique for a mixture of radioactive isotopes, because it does not require prior knowledge for the addition of inactive carriers as do most other radiochemical procedures. ... 

Collection of Methods on Radiochemical Analysis and Radiometric Measurements (1985), Voenizdat, Moscow (in Russian). 

The EPA developed two methods for the radiochemical analysis of uranium in soils, vegetation, ores, and biota, using the equipment described above. The first is a fusion method in which the sample is ashed, the silica volatilized, the sample fused with potassium fluoride and pyrosulphate, a tracer is added, and the uranium extracted with triisooctylamine, purified on an anion exchange column, coprecipitated with lanthanum, filtered, and prepared in a planchet. Individual uranium isotopes are separately quantified by high resolution alpha spectroscopy and the sample concentration calculated using the yield. The second is a nonfusion method in which the sample is ashed, the siUca volatilized, a tracer added, and the uranium extracted with triisooctylamine, stripped with nitric acid, co-precipitated with lanthanum, transferred to a planchet, and analyzed in the same way by high resolution a-spectroscopy (EPA 1984). 

Brown RM, Long SE, Pickford CJ. 1988. The measurement of long lived radionuclides by non-radiometric methods. In 5th Symposium Environmental Radiochemical Analysis, Part B, Harwell, England, UK, October 1-3, 1986. Sci Tot Environ 70 265-274. 

World Health Organisation, Methods of Radiochemical Analysis. Geneva, 1966. 

Radiochemical methods of analysis are considerably more sensitive than other chemical methods. Most spectral methods can quantitate at the parts-per-mil-lion (ppm) level, whereas atomic absorption and some HPLC methods with UV, fluorescence, and electrochemical methods can quantitate at the parts-per-billion (ppb) levels. By controlling the specific activity levels, it is possible to attain quantitation levels lower than ppb levels of elements by radiochemical analyses. Radiochemical analysis, inmost cases, can be done without separation of the analyte. Radionuclides are identified based on the characteristic decay and the energy of the particles as described in detection procedures presented above. Radiochemical methods of analysis include tracer methods, activation analysis, and radioimmunoassay techniques. 

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