Trace determination of uranium preconcentrated using graphene oxide by total reflection X-ray fluorescence spectrometry

A new method based on dispersive microsolid phase extraction using graphene oxide (GO) as a solid adsorbent and total reflection X-ray fluorescence (TXRF) spectrometry is proposed for trace determination of uranium. In the developed methodology, a suspension of GO was injected into uranium-spiked multielement solutions including rubidium; after filtration, the membrane filter with collected GO was placed in a small volume of internal standard acid solution and the eluent containing uranium was deposited onto a fluorine resin-coated slide glass, which is a disposable sample stage. Using GO was effective for removal of rubidium from the measurement solution to avoid interference between Rb Kα peak and U Lα peak. The high enrichment factor of 150 enables obtaining uranium detection limits of 0.042, 0.087, and 0.12 μg L⁻¹ for ionic strength of 0.01, 0.1, and 1 mol L⁻¹, respectively. Such low detection limits were obtained by using a benchtop TXRF spectrometer with 5-min measurement. The proposed method is suitable for trace uranium determination in water, including high salinity samples.     

Trace element determinations in uranium by total reflection X‐ray fluorescence spectrometry using polychromatic X‐ray excitation

Suitability of polychromatic X‐rays has been assessed for the total reflection X‐ray fluorescence (TXRF) trace elemental determinations in aqueous solutions as well as uranium oxide certified reference materials. The method involves total reflection of X‐rays below a certain energy level on the TXRF sample support and exciting the analytes present in ng amount on these supports, measuring the TXRF spectra, processing the spectra, and finally determining the elemental concentrations. For uranium‐based samples, the samples were dissolved, main matrix uranium was separated from these solutions using solvent extraction, and trace elements were determined using aqueous phase following above approach. The method is simple and easier to implement compared with the monochromatic excitation but has similar or in some cases better detection limits compared with those obtained using monochromatic excitation. The details of the methodology, quality of analytical results, and detection limits are described and compared with those obtained using monochromatic excitation. Copyright © 2017 John Wiley & Sons, Ltd.     

Determinations of low atomic number elements in real uranium oxide samples using vacuum chamber total reflection x‐ray fluorescence

Conditions for the total reflection x‐ray fluorescence (TXRF) analysis of real uranium samples for low atomic number elements using vacuum chamber TXRF spectrometer were optimized. It was observed that for analysis of low atomic number elements, almost complete removal of uranium matrix is required. Two certified reference materials of uranium containing trace elements in different concentrations were dissolved in minimum amount of high purity nitric acid. The uranium matrix from these solutions was separated by solvent extraction using tri‐n‐butyl phosphate as extracting reagent. Low atomic number elements in TXRF spectrum of the aqueous phase could be seen only after six tri‐n‐butyl phosphate equilibrations in extraction. The TXRF determinations of the certified low atomic number elements Mg and Al were made in these aqueous solutions after addition of Sc as an internal standard. The TXRF determined values for Mg were in good agreement with the certified values, whereas TXRF determined Al values differed from the certified values appreciably, probably due to the interference of Al Kα peak with escape peak of U Mα and the neighboring Si Kα peak. Copyright © 2013 John Wiley & Sons, Ltd.     

Trace elemental determination by portable total reflection X‐ray fluorescence spectrometer with low wattage X‐ray tube

A specimen containing nanograms of Sb, rare earth elements, Pb, and Bi and a specimen containing a few nanograms each of As and Pb were measured using a portable total reflection X‐ray fluorescence spectrometer. Nanograms of Sb, rare earth elements, Pb, and Bi were detected. Although the As Kα line (10.54 keV) overlapped with the Pb Lα line (10.55 keV) in a spectrum of the specimen containing nanograms of As and Pb, the Pb Lβ line was detected. Therefore, the net intensity of the As Kα line was calculated using the Pb Lα/Lβ intensity ratio in a spectrum of a Pb standard solution and the net intensity of the Pb Lβ line in the spectrum of the specimen containing As and Pb. This result indicates that these two elements can be quantified by using the portable spectrometer. Commercially available bottled drinking water was also measured. The portable spectrometer detected several tens of ppb of V in the drinking water sample. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of total reflection X-ray fluorescence spectrometry for trace elemental analysis of rainwater

Applicability of total reflection X-ray fluorescence (TXRF) spectrometry for trace elemental analysis of rainwater samples was studied. The study was used to develop these samples as rainwater standards by the National University of Singapore (NUS). Our laboratory was one of the participants to use TXRF for this study. The rainwater sample obtained from NUS was analysed by TXRF and the trace elements Mn, Fe, Ni, Cu, Zn, V and Pb were determined as required by the NUS. The average precision was found to be within 16% and the TXRF-determined elemental concentrations of these elements were below 20 μg/l. The average deviation of TXRF-determined values from the certified values were 20% (excluding the deviation for Fe and V which were comparatively high). Apart from the above elements, S, K, Ca, Rb, Sr, Ba and Br were also determined by TXRF and were found to be in the range of 0.2 to 191 μg/l. TXRF-determined values of our laboratory played an important role in the certification of concentration of seven elements in this rainwater sample which was later developed as a rainwater standard.     

Film thickness measurement by frustrated total reflection fluorescence

If the interface between a dielectric surface and an adjacent, fluorescing, medium of lower refractive index is illuminated by a collimated light beam, an exponentially decaying evanescent wave is generated in the fluorescing medium. The electric field of the evanescent wave generates easily measurable fluorescence. If part of the surface is covered with a dielectric film, the fluorescence generated is smaller, since some of the decaying wave occurs in a non-fluorescing medium. Measurement of the difference between the fluorescing signals enables the non-destructive measurement of the film thickness to be made. Several questions arise, for example (i) what angle of incidence should be used, (ii) how is the sensitivity influenced by the substrate refractive index, (iii) should p-or s-polarized light be used, (iv) what sensitivity is attainable? This paper answers these questions and indicates that films of the order of a nanometre in thickness are detectable.     

Monitoring dissolved active trace elements in biogas plants using total reflection X-ray fluorescence spectrometry

Generally, full-scale biogas plants require trace elements supplementation to sustain a stable process. The aim was to apply total reflection X-ray fluorescence (TXRF) to monitor the dissolved, active elements, for the first time, at μg/L levels in biogas plants. The digester liquid is comparable to sludge with high solids content and high salt concentrations. The ions are usually measured in the dried fermenter slurry after acid digestion in its inactive bound form, although microorganisms can take up only dissolved ions as active agent. In this study, a procedure was developed to monitor dissolved ions in such environmental processes to prevent an overdose or underdose. The analytical figures of merit considered were the lowest possible limit of detection, the recovery of spiked ions and linearity. Samples were spiked with nickel, selenium and tungsten in the range of 10–200 μg/L. Highest recovery rates of >93% for concentrations of 10 to <100 μg/L were obtained after the samples were centrifugated twice, followed by application of microwave-assisted acid digestion. The calculated lowest limit of detection was 2–4 μg/L. The developed method was first tested in laboratory-scale biogas digesters with wheat straw as substrate. Successful application of TXRF was also achieved in a full-scale biogas plant to estimate the dynamics of “active” trace element ions in the range of 2–1,000 μg/L for several months. Therefore, cost-effective biogas plant management is possible through the application of TXRF spectrometry to monitor trace elements.     

Total reflection X-ray fluorescence and energy-dispersive X-ray fluorescence characterizations of nuclear materials

Nuclear energy is one of the clean options of electricity generation for the betterment of human life. India has an ambitious program for such electricity generation using different types of nuclear reactors. The safe and efficient generation of electricity from these reactors requires quality control of different nuclear materials, e.g. nuclear fuel, structural materials, coolant, moderators etc. These nuclear materials have to undergo strict quality control and should have different specified parameters for their use in nuclear reactors. The concentration of major and trace elements present in these materials should be within specified limits. For such chemical quality control of these materials, major and trace elemental analytical techniques are required. Since some of these materials are radioactive, the ideal chemical characterization techniques should have multielement analytical capability, should require very less sample (micrograms level) for analysis so that the radioactive waste generated, and radiation exposure to the detector and operator are minimum. Total reflection X-ray fluorescence (TXRF) and energy dispersive X-ray fluorescence (EDXRF) with improved features, e.g. application of filters, secondary target and instrumental geometry require very small amount of sample and thus can be suitably used for the characterization of nuclear materials mainly for the determination of elements at trace and major concentration levels. In Fuel Chemistry Division, TXRF analytical methods have been developed for trace element determinations in uranium and thorium oxides, chlorine determination in nuclear fuel and cladding materials, sulphur in uranium, uranium in sea water etc. Similarly, EDXRF analytical methods with radiation filters (to reduce background) and improved sample preapartion techniques, e.g. fusion bead and taking samples in the form of solution on filter papers have been used for developing analytical methods for the determination of U and Th in their mixed matrices, Cd in uranium etc. Some of these studies have been reported in this paper.     

X-ray absorption spectroscopy in dispersive mode and by total reflection

The association of the total reflection scheme with the dispersive mode allows one to record in short time the EXAFS and XANES spectra of the first 30 Å of a surface. In situ time resolved observations of the surface modifications under chemical or electrochemical treatments are thus accessible. This promising technique is illustrated through two examples: (i) the thermal oxidation of a metallic copper surface and (ii) the electrochemical inclusion of Cu⁺ ions within a 5000 Å organic conducting polymer (poly-3-methylthiophene) electrochemically deposited on a platinum surface.     

Assessment of essential micronutrient levels in common beans (Phaseolus vulgaris) in Kenya by total reflection X-ray fluorescence

In Kenya, where malnutrition and hidden hunger still pose a significant challenge to growth and development, beans are an essential source of food for most of the population. However, data on micronutrient in beans are limited, and although they are required in very small amounts, they are essential for growth and development of plants as well as human beings. The aim of this study was to determine the concentrations of Mn, Fe, Cu, and Zn, in common beans in Kenya. Samples of both fresh bean leaves and dry grains of the most common bean varieties were collected from small-scale farmers in Muguga and Kyevaluki in Kiambu and Machakos Counties, respectively. They were analyzed using total reflection x-ray fluorescence (TXRF), a technique of increasing interest for food analysis since it is fast, easy, and reliable. Standard methods of sample preparation were used, and average elemental concentrations were compared with established sufficiency ranges. Bean leaves and dry bean grains from both sampling areas had sufficient concentrations of the four analyzed elements. Except for the Fe concentrations, the concentrations of the others elements were in the lower end of the sufficiency range for all bean species. The results obtained from this study are essential information for both farmers and policy makers and can be incorporated in programs to guide policy aimed at improving the nutritional quality of beans and thus food security in Kenya.     

Features of X-ray fluorescence determination of rock-forming elements in powder samples of peat sediments

The features of rock-forming elements determination in powder samples of peat sediments are considered. Based on theoretical calculations and experimental data, the mineralogical and particle size effects on the X-ray fluorescence intensity have been estimated. For routine analysis, powder rock samples are usually milled to a particle size of 10–60 μm. Theoretically, estimated variations of rock-forming elements analytical lines intensities in different minerals are up to 30%, and the particle size effect cannot be eliminated simultaneously for all rock-forming elements. Experimental estimation shows that the impossibility of the particle size distribution control can lead to significant variations in the intensities of the analytical lines (3%–18%) that is mainly corresponding to theoretical estimation. Fine milling allowed us to achieve an average particle size of fewer than 20 μm and reduce the measurement uncertainty by 1.5–2 times. 12 samples of peat sediments with organic matter content up to 70 wt% were analyzed by X-ray fluorescence analysis using different sample preparation techniques, as well as by certified methods. The accuracy of X-ray fluorescence analysis of peat sediments prepared as pressed pellets varies from 1.5 to 11 rel% depending on compound contents. It is more than for samples prepared as fused beads, however, the proposed method can be used to determine the variations of rock-forming elements contents in peat sediments where the content variations exceed the measurement uncertainty, and accuracy of analysis is sufficient for further paleoecological reconstructions.     

Critical angles of X-ray scattering in total reflection

The critical angles of Compton and fluorescent scattering in total reflection of X-rays are found to have a common value and to be the same as that of mirror reflection.     

A possible new case of total X-ray reflection

A new and quite simple method is proposed for consideration of multiple scattering of an incident ray by elements of a plane lattice. This method is used to obtain a general expression for the amplitude of coherent scattering of photons on an isolated monatomic layer. It is shown that at incident radiation frequencies coinciding with resonant frequencies of the lattice atoms a new phenomenon can develop: total reflection of photons from the isolated atomic layer, independent of the angle of incidence.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 21–25, April, 1985.The author is indebted to B. M. Bolotovskii for his valuable remarks and to V. L. Vinetstkii for his fruitful evaluation of the study.     

Determination of Gd and Sm contents in metallofullerenes on a total reflection X-ray fluorescence spectrometer with parallel beam

The contents of Gd and Sm have been determined quantitatively using the X-ray fluorescence analysis on a total reflection spectrometer with a parallel beam. It has been shown that the results can be used in developments of the technique for measuring the content of Gd metallofullerenes in powder samples several milligrams in weight and in liquid samples several microliters in volume.     

Energy dispersive X-ray fluorescence determination of Fe in solid powder samples: A quality improvement perspective

The various factors affecting energy dispersive X-ray fluorescence determination of iron in solid powder samples were evaluated, to improve the quality of these measurements. Influence of samples/standards preparation and instrumental parameters such as applied voltage to the X-ray tube, tube output current, and duration of acquisition were assessed, and the optimized instrumental parameters were 12 kV, 200 μA, and 200 s, respectively. Linear dynamic range of the spectrometer was found to be 0.0052 to 5.042 g kg⁻¹. Detection limits of iron in various organic/inorganic samples were found to be 2.5 to 21.9 mg kg⁻¹. The values obtained during the present method were evaluated with neutron activation analysis.     

Multivariate calibration for the improvement of the quantification of cadmium in the presence of potassium as interferent by total reflection X-ray fluorescence

A multivariate calibration method was applied to improve the accuracy of the determination of cadmium in the presence of potassium by total reflection X-ray fluorescence (TXRF). Due to TXRF's relatively low resolution, a particular interference caused by potassium at line Kα 3.31 keV as interference can compromise the cadmium determination at line Lα 3.13 keV, respectively. The method is based on the hypothesis that the application of a multivariate calibration method, for example, partial least squares, could reduce variations due to interference and, consequently, improve the selectivity and accuracy in Cd determination. In this work, this strategy was evaluated on the X-ray fluorescence emission signals between 2.50 and 3.90 keV for a set of 26 different synthetic calibration mixtures and eight different mixtures for external calibration. Based on a certified reference material (Clay 2—CRM051) with high potassium levels, a significant improvement of accuracy for cadmium determination was observed, overcoming the problems associated with spectral interferences by potassium.     

The quantification of total lead in lipstick specimens by total reflection X‐ray fluorescence spectrometry

Lipstick is known to contain lead, and this has been a general area of concern. Methods of quantifying lead in lipstick currently require the use of rather harsh digestion procedures given that lipstick specimens are high in their lipid content and contain many refractory materials. A simple method of performing lead analysis in lipstick specimens based on total reflection X‐ray fluorescence spectrometry (TXRF) is presented here. Samples were prepared by melting lipstick specimens along with a non‐ionic surfactant and an yttrium internal standard followed by homogenization. Solid prepared samples were then finely streaked directly onto a quartz reflector, and TXRF measurements made for 900‐s live time. The method was found to produce a mean limit of detection for lead of 0.04μg/g. Precisions were found to be on the order of 11–38% relative standard deviation (RSD) and apparent recoveries for lead between 92% and 106% (n = 8). Although the spreading technique may result in thickness variations that may contribute to the higher than expected variances about the determined lead concentrations, the method presented in this work does show promise as a means of performing routine lead analysis in lipstick specimens without the need for harsh digestion procedures. Copyright © 2015 John Wiley & Sons, Ltd.     

利用荧光CT实现生物医学样品内元素分布的无损成像

荧光CT是一种可无损重建元素空间分布的发射型断层成像技术,对生物医学研究具有重要意义.同步辐射的高通量、高准直和能量可调等特性使荧光CT的生物医学应用成为可能.文章通过优化设计,在上海同步辐射光源建立了一套用于生物医学样品微量元素分析的荧光CT成像系统.通过对实验装置的优化,提高了系统的数据采集速度和空间分辨率.将极大...     

Adsorption of firefly luciferase at interfaces studied by total internal reflection fluorescence spectroscopy

The adsorption of luciferase onto silica surfaces was studied by total internal reflection fluorescence (TIRF) spectroscopy. Two model surfaces were used: hydrophilic and hydrophobic silica. Luciferase adsorbed differently on these two surfaces. Initial kinetics of luciferase adsorption onto the hydrophilic surface showed that luciferase adsorbs over an adsorption energy barrier of 3 kT The quantum yield of luciferase fluorescence decreased at the hydrophilic silica surface, which indicated that the protein conformation was altered during adsorption. Luciferase adsorption onto the hydrophobic silica surface proceeded with a small adsorption energy barrier and the fluorescence efficiency of adsorbed protein remained unchanged after adsorption. The affinity of luciferase for luciferin was measured using quenching of luciferase fluorescence with luciferin. The binding constant of the adsorbed luciferase-luciferin complex at the hydrophilic silica surface was two orders of magnitude smaller than the respective binding constant in the solution. Adsorbed luciferase showed an absence of ATP-dependent visible luminescence, indicating that the adsorbed enzyme was not active at either of the two silica surfaces.