A comparative study on the total reflection X‐ray fluorescence determination of low Z elements using X‐ray tube and synchrotron radiation as excitation sources

Detailed total reflection X‐ray fluorescence (TXRF) studies for the detection and quantification of low atomic number elements were carried out by using a laboratory dual source TXRF spectrometer equipped with a vacuum chamber and at the International Atomic Energy Agency multi‐purpose end‐station facility, operated at the XRF beamline of Elettra Sincrotrone Trieste, Italy. Multi‐elemental standard aqueous solutions of low Z elements (F, Na, Al, S, K, Sc, and Ti) with different elemental concentrations of 2, 10, 20, and 30 µg/ml were prepared and measured in both setups. The measurements at the synchrotron setup were performed in a scanning mode across the sample residue and perpendicular to the incident beam in order to account properly for a possible non‐uniform deposition of certain elements. The accuracy and the detection limits obtained from the TXRF measurements in both setups were determined and comparatively evaluated and assessed. Significant improvement in the TXRF detection limits at the synchrotron beamline end‐station was obtained for the elements with Z ≤ 13 (Al). Copyright © 2017 John Wiley & Sons, Ltd.     

Trace determination of uranium in fertilizer samples by total reflection X-ray fluorescence

Uranium is reported to be present in phosphate fertilizers. The recovery of uranium from the fertilizers is important because it can be used as fuel in nuclear reactors and also because of environmental concerns. For both these activities suitable method of uranium determinations at trace levels in these fertilizers are required. Studies have been initiated for such TXRF determination of uranium and the results are reported in the present paper. For TXRF determinations the fertilizer samples were processed with nitric acid and the uranium present in it was removed by solvent extraction using tri-n-butyl phosphate as the extractant. The organic phase containing uranium was equilibrated with 1.5% suprapure nitric acid to bring out uranium in aqueous phase. This aqueous phase was mixed with internal standard Y and the TXRF spectra were measured by depositing samples on float glass supports. The amounts of uranium in four fertilizer samples of Hungarian origin were determined by processing these TXRF spectra. Uranium concentrations in two fertilizer samples were found to be in the range of 4–6 μg/g, whereas two fertilizer samples did not show the presence of uranium. The precision of the TXRF determination of uranium was found to be better than 8% (1σ).     

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.     

Determination of essential elements (Mn,Fe, Cu and Zn) in herbal teas by TXRF,FAAS and ICP-OES

The aim of this study was the comparison of the results obtained in the determination of the content of essential elements such as Mn, Fe, Cu and Zn in vegetation samples using different analytical approaches, including suspension preparation and total reflection X-ray fluorescence ( TXRF) analysis as well as most commonly used spectroscopic methods in the field of vegetal analysis such as acid digestion in combination with atomic emission (AES) and atomic absorption spectrometry (AAS). In the case of TXRF analysis, two instruments equipped with different X-ray tubes anodes (W and Mo) were used to better evaluate the potential of TXRF for vegetal samples analysis. Analytical figures of merit for the considered methods were determined by the analysis of plant reference materials. The one-way analysis of variance (ANOVA) applied to the analysed and certified values showed that the results were not statistically different at the significance level of p-values <0.05. Therefore, suspension preparation and TXRF analysis proved to be a sustainable and fast analytical alternative to the most commonly used ones involving a previous digestion of the sample and inductively coupled plasma optical emission spectrometry (ICP-OES) or flame atomic absorption spectrometry (FAAS) analysis. Finally, the different analytical approaches were applied to the determination of Mn, Fe, Cu and Zn in a set of herbal teas used for medical purposes.     

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.     

Characterization of Indian Ayurvedic herbal medicines for their metal concentrations using WD‐XRF spectrometry

This article describes the details of metal concentrations evaluated using wavelength dispersive X‐ray fluorescence (WD‐XRF) spectrometry. A total of 22 elements, Na, Mg, Al, Si, P, S, K, Ti, Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Hg, Pb, Ba, Au, and Sn from 16 Ayurvedic medicines were characterized. The method was validated by analyzing the six certified reference materials of soil standards [NIST SRM‐2710, CRM 027‐050 (US‐EPA certified), PS‐1, TILL‐1 and TILL‐4 (Canadian certified reference material, CCRMP) and JSO‐1 (Japanese certified reference material)]. The elemental concentrations in all the standards are found to be within ± 10% of the reported values. Crystalline phases in the individual drug samples were explained by powder X‐ray diffraction (XRD) technique. Qualitative phase identification was done using the ICDD database. Copyright © 2010 John Wiley & Sons, Ltd.     

Relative intensities in photoelectron spectroscopy of atoms and molecules

The relative intensities of photoelectron lines is discussed. The relationship of observed intensities to angle of observation is considered as are the errors introduced by ignoring the fact that different lines may have different angular distributions. Tables of theoretical results for the angular distribution asymmetry parameter, β, are presented for incident Al K_α, Mg K_α, and Zr M_ζ radiation for all atomic ground state subshells of non-zero angular momentum. The application of these results to molecules is discussed.     

Bestimmung von Elementspuren im Uran mittels Atom-Absorptionsspektrometric nach Vorabtrennung der Matrix

A method is described for the determination of Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb and Zn in uranium by atomic absorption or emission spectroscopy. The sample is dissolved in nitric acid. The uranium is selectively removed by extraction with tributyl phosphate. The aqueous layer is evaporated and the residue is re-dissolved in hydrochloric acid. All the elements can be determined in the solution. 1 – 2,5 g of uranium dioxide are used for the determination of 14 elements. The limits of detection are 0,2 – 5,0 ppm.     

A total reflection X‐ray fluorescence method for the determination of chlorine at trace levels in nuclear materials without sample dissolution

A total reflection X‐ray fluorescence (TXRF) method for the determination of chlorine at trace levels in nuclear fuel samples is described. Chlorine present in trace concentrations in nuclear fuel materials such as U₃O₈, (U,Pu)C, PuO₂ and Pu‐alloys was first separated from the solid matrix by pyrohydrolysis as HCl and was collected in 5 mM NaOH solution. This solution was analyzed for chlorine by TXRF spectrometry using Cl Kα analytical line excited by W Lα. Cobalt was used as internal standard. The precision for such chlorine determination was found to be within 27% (n = 4) when the analysis was carried out in air atmosphere. This could be improved to 8% by making TXRF measurement in flowing helium atmosphere. The results obtained from TXRF determinations were also compared with those obtained from ion chromatography (IC) and were in good agreement. The collection of distillate during pyrohydrolysis in NaOH helped in counterchecking loss of chlorine during TXRF sample preparation. The average deviation of TXRF‐determined values in helium‐purged TXRF measurements with IC determined values (as chloride) was 15% at a chlorine concentration level in the range of 1–70 µg/mL. Copyright © 2012 John Wiley & Sons, Ltd.     

A setup for synchrotron‐radiation‐induced total reflection X‐ray fluorescence and X‐ray absorption near‐edge structure recently commissioned at BESSY II BAMline

An automatic sample changer chamber for total reflection X‐ray fluorescence (TXRF) and X‐ray absorption near‐edge structure (XANES) analysis in TXRF geometry was successfully set up at the BAMline at BESSY II. TXRF and TXRF‐XANES are valuable tools for elemental determination and speciation, especially where sample amounts are limited (<1 mg) and concentrations are low (ng ml^?1 to µg ml^?1). TXRF requires a well defined geometry regarding the reflecting surface of a sample carrier and the synchrotron beam. The newly installed chamber allows for reliable sample positioning, remote sample changing and evacuation of the fluorescence beam path. The chamber was successfully used showing accurate determination of elemental amounts in the certified reference material NIST water 1640. Low limits of detection of less than 100 fg absolute (10 pg ml^?1) for Ni were found. TXRF‐XANES on different Re species was applied. An unknown species of Re was found to be Re in the +7 oxidation state.     

Determination of Pb,As, Cd and trace elements in polluted soils near a lead–zinc mine using polarized X‐ray fluorescence spectrometry and the characteristics of the elemental distribution in the area

Polarization energy dispersive X‐ray fluorescence spectrometry was used in the determination of Pb, As and Cd, as well as Cr, Cu, Zn, Ni and other minor and trace elements in the soil samples taken from a polluted area by lead mine exploitation. Two difficulties have to be overcome. One is strong overlap of Pb Lα over As Kα and another is lack of suitable certified reference materials. The different excitation conditions and analytical lines were tried to reduce the impact of overlap of Pb Lα over As Kα. When KBr was used as the second target, compared with Zr, the proportion from Pb Lα was reduced about six times. Even so, however, the overlap was not reduced enough to be ignored. The inductively coupled plasma atomic emission spectrometry and mass spectrometry methods were used to analyze parts of soil samples and provide data for compensating lack of reference materials. By this method, the analytical concentration range of Pb, As and Cd were significantly extended. The analytical range of Pb, As and Cd were 1.4 µg/g~4.2%, 0.6 µg/g~9.3% and 0.5 µg/g~1500 µg/g, respectively. The high concentrations of Pb, As and Cd were found in the samples in the vicinity of the Pb‐Zn mine. The concentrations of Pb, As, Cd, Zn and Cu were higher than the Class III in the Chinese environmental quality standard for soils. The highest concentrations of Pb, As, Cd and Zn in the soil samples were 14 960, 2726, 65 and 9439 µg/g, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

X‐ray fluorescence induced by standing waves in the grazing‐incidence and grazing‐exit modes: study of the Mg–Co–Zr system

The characterization of Mg–Co–Zr tri‐layer stacks using X‐ray fluorescence induced by X‐ray standing waves, in both the grazing‐incidence (GI) and the grazing‐exit (GE) modes, is presented. The introduction of a slit in the direction of the detector improves the angular resolution by a factor of two and significantly improves the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kα and Co Lα characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, it is shown that the interfaces of the Si/[Mg/Co/Zr]_×30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co]_×30 multilayer a strong intermixing occurs at the Co‐on‐Zr interfaces. An explanation of this opposite behavior of the Co‐on‐Zr and Zr‐on‐Co interfaces is given by the calculation of the mixing enthalpies of the Co–Mg, Co–Zr and Mg–Zr systems, which shows that the Co–Zr system presents a negative value and the other two systems present positive values. Together with the difference of the surface free energies of Zr and Co, this leads to the Mg/Zr/Co system being considered as a Mg/Co_xZr_y bi‐layer stack, with x/y estimated around 3.5.     

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.     

The investigation of K‐shell fluorescence parameters of Zn–Fe alloys with different grain size and microstrain values

It is known that zinc alloys with iron group metals have better corrosion resistance than pure zinc. Owing to the corrosion resistance of these alloys, Zn–Fe coatings are widely used in automotive industry and have excellent mechanical performance. In this work, we investigated the relationship between the changes in the measured X‐ray fluorescence parameters (K_β/K_α, σ_Kα and σ_Kβ) and the changes in the structural parameters such as microstrain or grain size values for Zn–Fe alloys that were prepared with different pH values. To explain these changes, the K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values were calculated by three different ways for the elemental forms of Zn and Fe. The structural parameters, such as microstrain and grain size, were also calculated. We expect that the outer shell electronic distribution affects the structural parameters of the produced Zn–Fe alloys, changing the measured K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values. We also show that Zn–Fe alloy mi nimum microstrain value corresponds to the maximum changes in K_βX‐ray production cross‐section values of Fe and Zn. Copyright © 2017 John Wiley & Sons, Ltd.     

Calibration of the MER α‐particle x‐ray spectrometer for detection of ‘invisible’ OH and H2O possibly present in Martian rocks and soils

An existing Monte Carlo code was modified and extended to predict the intensity ratio of elastically and inelastically scattered plutonium Lα x‐rays incident on rock samples in the Mars Exploration Rover's α‐particle x‐ray spectrometer (APXS) device. The systematics of the scatter ratio as a function of effective sample atomic number are explored. The simulated Rayleigh/Compton ratios (R/C)_sim are compared with measured ratios (R/C)_meas that are obtained by fitting APXS spectra of geochemical reference materials using an x‐ray fluorescence version of GUPIX. The quantity K = (R/C)_meas/(R/C)_sim is then plotted against the mean atomic number of the sample to provide a calibration for known samples. Departures of K values of unknown samples from this calibration may then be attributed to the presence of light, ‘invisible’ elements in the sample. This work is part of an ongoing project aimed at developing methods to quantify bound water in Martian rocks analyzed by the present and the next generation APXS instruments. Copyright © 2006 John Wiley & Sons, Ltd.     

Reference spectra of important adsorbed organic and inorganic phosphate binding forms for soil P speciation using synchrotron‐based K‐edge XANES spectroscopy

Direct speciation of soil phosphorus (P) by linear combination fitting (LCF) of P K‐edge XANES spectra requires a standard set of spectra representing all major P species supposed to be present in the investigated soil. Here, available spectra of free‐ and cation‐bound inositol hexakisphosphate (IHP), representing organic P, and of Fe, Al and Ca phosphate minerals are supplemented with spectra of adsorbed P binding forms. First, various soil constituents assumed to be potentially relevant for P sorption were compared with respect to their retention efficiency for orthophosphate and IHP at P levels typical for soils. Then, P K‐edge XANES spectra for orthophosphate and IHP retained by the most relevant constituents were acquired. The spectra were compared with each other as well as with spectra of Ca, Al or Fe orthophosphate and IHP precipitates. Orthophosphate and IHP were retained particularly efficiently by ferrihydrite, boehmite, Al‐saturated montmorillonite and Al‐saturated soil organic matter (SOM), but far less efficiently by hematite, Ca‐saturated montmorillonite and Ca‐saturated SOM. P retention by dolomite was negligible. Calcite retained a large portion of the applied IHP, but no orthophosphate. The respective P K‐edge XANES spectra of orthophosphate and IHP adsorbed to ferrihydrite, boehmite, Al‐saturated montmorillonite and Al‐saturated SOM differ from each other. They also are different from the spectra of amorphous FePO₄, amorphous or crystalline AlPO₄, Ca phosphates and free IHP. Inclusion of reference spectra of orthophosphate as well as IHP adsorbed to P‐retaining soil minerals in addition to spectra of free or cation‐bound IHP, AlPO₄, FePO₄ and Ca phosphate minerals in linear combination fitting exercises results in improved fit quality and a more realistic soil P speciation. A standard set of P K‐edge XANES spectra of the most relevant adsorbed P binding forms in soils is presented.     

第一性原理对XMgn(X=B,Al, n=1—12)团簇的几何结构和电子性质的研究

利用密度泛函理论(DFT)的B3PW91方法,在6-311G水平上对BMg_n,AlMg_n(n=1—12)团簇进行了几何结构优化和电子性质分析. 发现随着原子个数的增加, B原子进入镁团簇的内部, 而AlMg_n和镁团簇有相似的生长模式. B,Al原子的掺杂均能使镁团簇的平均结合能增大,稳定性增强, BMg_n,AlMg_n关键词： 密度泛函理论 最低能量结构 n和AlMg_n团簇')" href="#">BMg_n和AlMg_n团簇 NBO电荷布居     

X‐ray fluorescence spectrometry in Dar es Salaam

Energy‐dispersive x‐ray fluorescence (EDXRF) analysis has been established at the University of Dar es Salaam, Faculty of Science, Department of Physics. Calibration was conducted using thin films from Micromatter (USA) for secondary target XRF. We report on the performance of the spectrometer including the detection limits attained, which range from 0.01 to 10 ng cm^?2 using collimators of 6 and 8 mm diameter under excitation conditions of 50 kV, 35 mA. The accuracy of the measurements was checked using IAEA SOIL‐7 and NIST 3087a Certified Reference Materials. The experimental values differed by <5% from the certified values. The total reflection x‐ray fluorescence (TXRF) facility added as a module to the existing XRF system provides detection limits between 0.1 and 100 pg for most of the elements measured. Copyright © 2005 John Wiley & Sons, Ltd.     

Routine x‐ray fluorescence analysis of powder materials using the ‘VERBA‐XRF’ mode

A new version of the ‘VERBA‐XRF’ mode was developed for the determination of the contents of principal elements with atomic numbers Z > 10 and SUM9, that is, the sum of the contents of complementary elements with Z < 9 in powder materials without alloying with borax. An original set of equations provides determination of the SUM9. Analysis was made on 120 samples: dust from electric filters, clay, clinker, gypsum, bauxite, slag, candle‐end, shale, schlamm and chalk. The results obtained in the determination of the elements Fe, Ti, Ca, K, S, Si, Al and Mg have relative standard errors of 1–2%. The availability of the value of the SUM9 provided the possibility of determining chemical compositions in samples. The content of mineral white in natural gypsum was calculated. Copyright © 2004 John Wiley & Sons, Ltd.     

离化态原子Kα射线移位的规律

本文从理论上对离化态原子的K_α射线所发生的移位作了初步的研究,并总结了K_α射线随离化度和原子序变化的规律。提供了有关的数据图表,这可以用来估算各种离化态原子(原子序Z≤42)的K_α射线移位。最后还讨论了测量移位的K_α射线谱,这可以应用于等离子体的杂质诊断。 关键词：