Analytical Methods for the Determination of Uranium

Last but not least, an excellent comprehensive document that covers practically all facets of environmental behavior of uranium was published by the Canadian Council of Ministers of the Environment (Environment 2007). The chemical and physical properties of uranium were reviewed and its distribution in the environment and bio-accumulation in various flora and biota were discussed. For example, guidelines for the permissible uranium concentration in soil were set according to the intended land use. Eor agricultural use and commercial land use, the maximum uranium concentration was 33 mg kg for residential and parkland uses it was 23 mg kg , and a value of 300 mg kg was set for industrial land use. This document also contains many tables that summarize the toxicological effects of uranium on humans and the uranium content in several food products, vegetation, soil, water, etc. In addition, a summary of the analytical methods that are used for the determination of uranium in a variety of environmental samples, very similar to Table 3.1, is given (Environment 2007). 

The analytical methods used for the determination of uranium in environmental samples are basically the standard methods reviewed in brief in Chapter 1. The main differences are in the sample preparation procedures required for the analysis of the variety of environmental samples that include soil of different types, sediments, diverse types of vegetation, water from different sources with a wide range of acidity, salinity, suspended matter, etc. In addition, the environmental samples may include airborne particulate matter, vapors, and gases, as well as special samples involved in the food chain that may affect humans. Einally, the interplay of uranium (and other contaminants) between the environmental compartments—for example, the transfer factors of uranium from soil-to-plant or from vegetation to food products (e.g., free-range grazing cattle) are also part of the media that need to be characterized. 

A general overview of atomic spectrometric techniques, including atomic absorption spectroscopy (FAAS and ETAAS), atomic emission spectrometry (ICP-OES), and mass spectrometry (ICP-MS), for the determination of uranium was published (Santos et al. 2010). The advantages and limitations of each technique were discussed and compared and the complexity and costs were also considered. In addition, use of preconcentration and separation to improve performance was also described. 

As seen in the specific examples given later, numerous analytical methods are used for the determination of uranium in environmental samples. The most popular among them are ICPMS and alpha spectrometry, but neutron activation analysis, gamma spectrometry, and XRF are often deployed and even simple spectrophoto-metric (like colorimetric aresnazo-III) techniques are sometimes still used. For the precise determination of total uranium and its isotopic composition, isotope dilution (ID) methods can be used. One example is a comparison of ID-TIMS and ID-SIMS for isotope ratios in soil standards where two separation and preconcentration chromatographic techniques were also compared (Adriaens et al. 1992). 

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Lauria DC, Godoy JM. 1988. A sequential analytical method for the determination of uranium-238, thorium-232, thorium-230, thorium-228, radium-228, and radium-226 in environmental samples. Sci Total Environ 70 83-99. 

Source Mclnnes, D.A. and Longsworth, L.G., A Comparison of Analytical Methods for the Determination of Uranium, Rockefeller Institute for Medical Research, Oak Ridge, TN, 1942, MDDC-910 (declassified 1947). 

Analytical Methods for the Determination of Uranium in Drinking Water... 

Once these samples are collected, an arsenal of the analytical procedures for the determination of uranium is available. Some of these were described in this chapter, but given the variation in the types of samples, in the sample treatment procedures and in the analytical methods, there is no universal routine for all. In order to report meaningful results for the uranium content in vegetation and food... 

Electroanalytical Methods Many publications described the use of electro-analytical methods for measuring uranium in water and some examples are discussed here. A detailed review article with illustrative tables that summarize the electroanalytical methods for the determination of uranium can be found elsewhere (Shrivastava et al. 2014). The tables in that review article list the method, the principles of the measurement technique, the linear range, limit of detection, tolerance to interferences (where defined), and the field in which the method is applied. 

Manning, Ball, and Menis (162) have carried out polarographic and coulometric reductions of molybdenum (VI) in a nitrilotriacetic acid medium and have applied their findings to the analysis of thorium-uranium oxide mixtures. The determination of molybdenum in steel using coulometric techniques has been reported by Ibrahim and Nair (163) who reduced molybdenum at —0.40 V vs. SCE in a sodium acetate buffered chloride medium. Chromium interference can be removed by pre-reduction with alcohol. The catalytic effect of lower oxidation states of molybdenum in the reduction of perchlorate has been used as an indirect electro-analytical method for the determination of perchlorate (159, 164). 

Several analytical methods have been deployed for the determination of uranium in ores. Among the older methods that were used are radiometric methods that were already used over 50 years ago for ore sorting (Mal tsev 1960), titrimetric methods in which the nraninm content in the ore was determined with ferrous ion-phosphoric acid reduction (Hitchen and Zechanowitsch 1980), colorimetric methods where complexes of nraninm are formed with standard arsenazo 111 (Onishi and Sekine 1972), exotic siderophores (Renshaw et al. 2003) reagents and instrumental neutron activation analysis (INAA) based on measurement of Np in the ore (Chaudhry et al. 1978) in addition to nnmerons other approaches. Many modem techniques are now employed for destrnctive and nondestructive determination of uranium in ores. 

The methods of assessing exposure to uranium are derived from the biokinetic models that were discussed earlier. Analytical procedures for the determination of the uranium content in excreta mainly urine and sometimes also feces, blood (serum or plasma),... 

A number of the prooeradiometric determination of wanlum. The method of separation in these procedures, however, is applicable to radiochemical analysis and is, therefore, included. A number of papers and reports describe, in detail, procedures for the determination of uranium. These should be noted. The work of Rodden and Warf has frequently been mentioned in this paper. In addition to procedures for the precipitation, solvent extraction, volatilization, and electrodeposltlon of uranium, these authors have presented a number of selected procedures for the solution of ores and minerals and the separation and determination of uranium. Procedures for the analytical determination in naturally occurring materials have also been described by Hodden and Tregonning,- Grimaldi, May, Fletcher, and Tltcomb, 2Z. Sohoeller and Powell,and in the "Handbook of Chemical Determination of Uranium in Minerals and Ores." 2 The recent publication by Hoore on extraction with amines contains a collection of procedures., many of which have to do with the separation of uranium. 

TIMS has been used for many years as the benchmark technique especially for uranium isotope analysis. Instrumental improvements have enabled ICP-MS to approach the accuracy and precision obtained by TIMS in measuring data. In addition, due to time consuming sample preparation steps and the need for a large volume of urine, the method has been replaced by the more powerful ICP-MS in many laboratories. An interlaboratory analytical exercise on the determination of natural and depleted uranium in urine was carried out by different ICP-MS instruments, by thermal ionization mass spectrometry (TIMS) and instrumental neutron activation analysis. TIMS has also been employed to determine fg quantities of Pu and °Pu in bioassay samples (such as human urine and artificial urine), ° in an interlaboratory comparison for the analysis of the Pu and Pu/ °Pu atomic ratios in synthetic urine by TIMS and AMS as reported in reference. ... 

Other analytical techniqnes are also available for characterizing UO2 powders and pellets, so adherence to the ASTM procedures is not the only way to ascertain compliance with the specifications. An overview of the spectrometric techniqnes and sample preparation procedures (including separation of the uranium matrix) for the determination of impurities in nnclear fuel grade materials summarizing several methods was pnbUshed (Souza et al. 2013). Among the spectrometric techniqnes surveyed are FAAS, GFAAS, ICP-OES, and ICP-MS as well as strategies for matrix separation and preconcentration steps. 

Several of the methods mentioned earlier for the determination of the uranium content in soil are also suitable for assaying the uranium content in plants. However, there are two major differences the uranium concentration in plants is usually significantly lower than in soil and the fraction of organic matter and the moisture content in plants are much higher than in soil. These two factors dictate somewhat different sample preparation methodologies and more sensitive analytical devices are preferred as shown in the following examples. Some of the review articles mentioned earlier also discuss the uramum content, uptake (transfer factor), and distribution in plants (Zavodska et al. 2008 Mitchell et al. 2013). One of the most comprehensive sources listing the uranium content in many different types of plants is the Canadian report mentioned earlier (Environment 2007). An additional important source can be found in the report published by the IAEA (IAEA 2010). 

As mentioned earlier, there are several analytical methods that have been developed for the analysis of uranium in urine. Some of the older methods required separation and preconcentration of the uranium from the urine sample, but modern methods, based mainly on ICPMS, allow direct determination of the uranium in raw urine or after simple dilution. In the following section, some of the older analytical methods for determining uranium in urine will be described. This section is based in part on a review that was carried out at Oak Ridge National Laboratory (Bogard 1996). 

The application of the Chelex 100 resin separation and preconcentration, with the direct use of the resin itself as the final sample for analysis, is an extremely useful technique. The elements demonstrated to be analytically determinable from high salinity waters are cobalt, chromium, copper, iron, manganese, molybdenum, nickel, scandium, thorium, uranium, vanadium, and zinc. The determination of chromium and vanadium by this technique offers significant advantages over methods requiring aqueous final forms, in view of their poor elution reproducibility. The removal of sodium, chloride, and bromide allows the determination of elements with short and intermediate half-lives without radiochemistry, and greatly reduces the radiation dose received by personnel. This procedure was successfully applied in a study of... 

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