Uranium colorimetric

In the analysis of total uranium, colorimetric detection methods are also possible, depending on the detection limits required. This is a case of measuring a radioactive element, as opposed to a specific radioisotope of an element. In this case, separation methods are used to preconcentrate the uranium to increase the analysis sensitivity and decrease the detection limits.18 21... 

Discussion. Small amounts of chromium (up to 0.5 per cent) may be determined colorimetrically in alkaline solution as chromate uranium and cerium interfere, but vanadium has little influence. The transmittance of the solution is measured at 365-370 nm or with the aid of a filter having maximum transmission in the... 

Some of the methods commonly used for the determination of thorium in biological materials are given in Table 6-1. The colorimetric methods are not capable of isotope-specific determination of thorium isotopes. Alpha spectrometric and neutron activation analysis are useful in the quantification of isotope-specific thorium and thorium-232, respectively, and have better sensitivities than colorimetric methods. Alpha spectrometry is the commonly used isotope-specific analysis for the determination of thorium-232 and the thorium-230 derived from the decay of uranium-238 (Wrenn et al. 1981). Standard reference materials (SRMs) containing thorium in human liver (SRM-4352) and human lung (SRM-4351) necessary for the determination of absolute recovery in a given sample are available from the National Institute of Standards and Technology (Inn 1987). 

A colorimetric method of estimating small quantities of uranium in solution depends upon the red colour obtained when a uranyl salt is treated with sodium salicylate. Free mineral acid, iron, acetic add, alcohol, or acetone must be absent, but neutral alkali salts do not interfere. 

Although most of the elements have been determined by XRF (21), some other methods were used. The fluorometric method for selenium uses diaminonaphthalene (32). The colorimetric method for molybdenum uses potassium thiocyanate (33). The uranium analyses were done by delayed neutron activation analysis (34). For the XRF analyses of the oil and water, a blank value implies that there were no x-rays above background for that element. Two elements conspicuously missing from Table IV are cadmium and mercury. Preliminary analyses for these two elements have not yielded reproducible results. Further work is needed before we can make definitive statements about cadmium and mercury. 

A liquid emulsion membrane based on trioctylphosphine oxide extractant was applied for separation of uranium and thorium from Ce, Cu and Cd [2]. Highly selective U02 imprinted polymer (synthesized using uranium vinylbenzoate, divinylbenzene in styrene and 2,2 -azobisisobutyronitrile) was proposed for purification, preconcentration and determination of the uranyl ion [3]. Dibenzoylmethane was used as a colorimetric reagent. The detection limit of 160 ppt was achieved. 

Lucy et al. (1993) report on a multicolumn method for chromatographic analysis of irradiated nuclear fuels. The first stage is characterized as a semi-preparative reversed-phase separation that removes the uranium matrix. A second column concentrates and separates the lanthanides prior to colorimetric detection of the ions using Arsenazo III. Instead of the 0.5—100 g of uranium required for conventional analysis of lanthanide content in such samples, these authors indicate a detection limit of 20ng/g (uranium) for Sm, Gd, Eu, and Dy from a 20mg uranium sample. They indicate no interferences in the analysis from transition or alkaline-earth metals. The uranium solution (containing the lanthanides) is initially dissolved in 0.025 M hiba. The reverse-phase column passes the lanthanides in a band and retains Th and U. The lanthanide band from the precolumn is channeled to the analysis column and sq)arated with an hiba gradient elution sequence. 

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. 

A simple spectrophotometric (or colorimetric) method for the determination of uranium in perchloric acid based on the arsenazo-III complex was described (Khan et al. 2006). While azo-dyes may be oxidized by nitric acid, they are more stable in perchloric acid and organic interferences are effectively eliminated by this acid media. Standards of uranium and ore samples were weighed and decomposed in Teflon beakers with a 1 1 HNOjiHF mixture. The uranium was then extracted from the nitrate solution by liquid-liquid extraction with TBP in methyl isobutyl ketone (MIBK). The uranium... 

The main specifications concern the uranium content in UFg by gravimetric and titrimetric methods, isotopic composition (as listed earlier), el ental impurities by atomic absorption, ICP-AES, spectrographic, colorimetric, titrimetric, spark source mass spectroscopy and radiochemical (alpha and gamma spectrometry and neutron absorption) methods, and organic impurities like hydrocarbons and their derivatives. Modern methods also deploy ICPMS techniques for the determination of impurities and isotopic composition (C1287 2010). It is beyond the scope of this book to present all these methods in detail so a number of examples are shown later. 

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). 

An SPE method for online preconcentration of uranium in water and effluent samples is based on amberlite XAD-4 resin functionalized with p-nitroso-a-naphtol (Lemos and Gama 2010). A preconcentration factor of 10 was achieved and with a colorimetric arsenazo-III spectrophotometry a detection limit 1.8 pg L" was reported. The online system included a mini-column through which the solution was passed for 180 s. In the elution step, the uranium was desorbed from the column and mixed with the colorimetric reagent and introduced into the spectrometer. The parameters were optimized and the effects of several interferences were examined. Recovery of spiked tap water, well water, and effluent samples was close to 100% (Lemos and Gama 2010). 

Colorimetric Method (Photometry) A rapid, simple colorimetric method for the determination of uranium in groundwater and drinking water that can be nsed in the laboratory and in the field was described (Ratliff 2008). The first step is selectively trapping the uranium on a chromatographic resin (U/TEVA-2 in this example) followed by the formation of a colored complex with a pyridylazo indicator dye (Br-PADAP). At neutral pH, the complex absorbs light at 578 nm and is clearly visible. Qnantiflcation can be achieved with a spectrophotometer. The method can detect nraninm concentrations above the US-EPA guideline for drinking water of 30 pg L In Section 4.4.1, another colorimetric method that is snitable for the determination of nraninm in water and nrine based on the formation of a complex with Arsenazo-III is presented. 

Cation-exchange chromatography in combination with a postcolumn derivatization is also suitable for analyzing uranium and thoriiun [46]. Because both elements are actinides and in close relation with lanthanides, they are always associated with them. Due to the lack of simple and sensitive colorimetric methods, the trace analysis of these elements represents a challenge. Although alternative analytical methods for these elements such as neutron activation analysis (NAA) [47] and ICP-MS [48] are described in literature, they are not suitable for routine analysis and are prone to interferences. Major interferences include... 

Concentrations by radiochemical method and volumetrically by the hydrosulflte-phosphate-vanadate method for uranium radiochemically and colorimetrically with arsenozo III for thorium and by oscillographic polarigraph for lead. 

Johnson, D.A., and T. Florence. A specific and quantitative colorimetric measurement for hexavalent uranium. 1971. M. Anal. Chim. Acta. 53 73-79. 

The amount of uranium In a sample may be determined by standard methods of analysis gravimetric, volumetric, colorimetric, spectrophotometrlc, etc. ... 

For the nltrlo acid treatment, dissolve the sample In a suitable quantity of nitric acid and transfer the solution and Insoluble residue into an appropriate volumetric flask and make up to volume. Regulate the dilution so that the aliquot chosen for extraction will contain between 10 and 30 mg. of uranium oxide If the final dilution for the colorimetric finish Is to be 250 ml. Adjust the acidity of the 8ang>le solution to about In nitric acid. 

Water Stripping of Uranium from Ethyl Acetate Layer Followed by Sodium Hydroxide-Hydrogen Peroxide Colorimetric Finish, Add 15 ml. of water to the separatory funnel containing the ethyl acetate, stopper the flask, and shake the mixture for about 1 minute. After washing off the stopper with water, drain the aqueous layer Into a volumetric flask of suitable size and wash the separatory funnel and ethyl acetate layer 4 or 5 times with 5-ml. portions of water by means of a wash bottle. Combine the aqueous fractions. 

Double EKtractlon of Urmlum with Ethyl Acetate Followed by Applloatlon of Differential Colorimetry. Uranium determinations requiring the highest accuracy may be carried out by a double extraction of uranium with ethyl acetate followed by the application of differential colorimetry is described by Hlskey and others.— In such a case It Is recommended that between 100 euid 150 mg. of uremlum oxide be extracted, and a wave length of 4 00 mt be used during the colorimetric finish. The procedure described below has been found satisfactory. 

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