Determination of lead at physiological level in human biological materials using the total reflection X‐ray fluorescence analysis

Total reflection X‐ray fluorescence (TXRF) analysis was applied in determination of low concentration of lead in samples of human biological materials. The determination of lead in human serum and hair samples is presented as an example. In serum samples, lead concentration was in the range from 0.013 to 0.051 μg/g (median 0.024 μg/g). The reference ranges of lead content in hair are from 1.41 to 4.08 μg/g for men and from 1.18 to 3.29 μg/g for women groups, respectively. Because of Pb concentration range close to the detection limit of the TXRF method, the measurement needed evaluation of the best analytical conditions. This paper presents the results of this evaluation, namely internal standard selection, measurement conditions, and quantitative calibration of the spectrometer. Finally, as a result of evaluation, the detection limit was found on the level 0.001 μg/g (water solution) and about 0.005 μg/g for human hair samples and 0.007 μg/g for serum samples. The obtained values reach nearly the physiological lead level. The presented results are of practical importance for lead concentration studies in human biological materials using the TXRF method. Copyright © 2016 John Wiley & Sons, Ltd.     

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 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).     

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.     

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.     

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.     

Study of factors affecting the results of natural water analyses by total reflection X‐ray fluorescence

The study aims to choose the conditions for the direct analysis of different types of natural water samples by total reflection X‐Ray fluorescence spectrometry (TXRF). The effect of some factors on TXRF results was studied such as the surface density of dried water residue on the sample carrier, the dilution ratio of high‐mineralized samples with ultrapure water and the solution of the detergent Triton X‐100, the salt contents, the internal standard concentration, and repeated pipetting of an aliquot of fresh water. The influence of self‐absorption phenomena on quantification results was demonstrated by using brine samples. The TXRF results for natural waters of varying salinity (brines, fresh waters, and ground waters) and model solutions are presented. For a number of analytes, the data obtained by TXRF were compared to those obtained by ‘wet’ chemistry and inductively coupled plasma mass spectrometry. Copyright © 2013 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.     

TXRF intensity dependence on position of dried residue on sample carrier and TXRF determination of halogen in liquid samples

Total reflection X‐ray fluorescence (TXRF) spectroscopy is an effective technique for simultaneous multi‐elemental trace analysis of a small volume of a sample placed on a flat substrate. An internal standard method is usually applied for quantitative TXRF analysis of liquid samples such as drinking water and environmental samples. However, it was difficult to determine Cl and Br because they were lost as volatile hydrogen halide compounds by adding an acid internal standard solution. Thus, we attempted to apply the traditional calibration curve method for the determination of halogens without internal standard. If internal standard method is not applied, the TXRF intensity drastically changes depending on the relative position of the dried residue to the detector. Therefore, we investigated the relationship between TXRF intensity and the position of dried residue relative to the detector. As a result, it was confirmed that TXRF intensity critically depended on the position of the dried residue on the sample carrier. The position of the droplet of the sample solution was carefully controlled by using an air blower in order to place the dried residue at the most effective position on the sample carrier. We could successfully make a calibration curve for Cl with a good relationship without internal standard. Finally, Cl in the NaCl solutions (0 –5 ppm, 10 µl) was successfully determined by the calibration curve method using a table‐top TXRF instrument. The limit of detection of Cl was 63 ppb (ng/ml). Copyright © 2016 John Wiley & Sons, Ltd.     

Application of synchrotron‐radiation‐induced TXRF‐XANES for arsenic speciation in cucumber (Cucumis sativus L.) xylem sap

Synchrotron‐radiation‐induced total reflection x‐ray fluorescence (SR‐TXRF) analysis was used for x‐ray absorption near edge structure (XANES) measurements for the speciation of arsenic in cucumber (Cucumis sativus L.) xylem sap. The objective of the presented work was to exploit the advantages of the TXRF geometry for XANES analysis. Measurements were accomplished at the bending magnet beamline L of HASYLAB, Hamburg, Germany, using a Si(111) double crystal monochromator and a silicon drift detector (SDD). Experiments were performed by growing cucumber plants in hydroponics containing arsenite [As(III)] or arsenate [As(V)] in order to identify the arsenic species of the collected xylem saps by K‐edge SR‐TXRF XANES. Cucumber xylem saps, as well as nutrient solutions containing arsenic in the two above‐mentioned species, were analyzed and compared with arsenate and arsenite standard solutions. Arsenic speciation in xylem sap down to 30 ng/ml (30 ppb) was achieved, and no alteration of the oxidation state was observed during the measurements. Analysis of xylem saps showed that As(V) taken up from the nutrient solution was reduced to As(III). As(III) contained in the nutrient solutions was found to be partially oxidized to As(V). These results confirmed the preliminary measurements obtained with flow injection analysis (FIA) and high‐performance liquid chromatography‐high resolution inductively coupled plasma mass spectrometry (HPLC‐HR‐ICP‐MS) and showed the competitive capability of SR‐TXRF XANES analysis for this application. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Chromium speciation by TXRF analysis

Chromium (Cr) is an element which usually occurs in two different forms, Cr(III) and Cr(VI). As Cr(VI) is much more toxic than Cr(III), no complicated analytical methods with low detection limit are needed for chromium speciation. In the present work, a new method is presented for chromium speciation at low concentrations by selective membrane collection and total Reflection x‐ray fluorescence (TXRF) analysis. Various membranes were produced on the surface of quartz reflectors containing different complexing ligands in Nafion and poly vinyl chloride (PVC) matrices. The membranes were produced on the surface of quartz glass, while the reflectors were immersed in water solutions with low concentrations of chromium salts for many hours. When the equilibration stage was achieved, the reflectors were analyzed by TXRF. Completely selective membranes for Cr(III) and Cr(VI) were prepared with minimum detection limits lower than 0.6 ng.ml^?1 (ppb) in drinking water. Copyright © 2009 John Wiley & Sons, Ltd.     

微波消解ICP-MS测定尿样中硒及其他重金属元素

建立微波消解电感耦合等离子体-质谱法(ICP-MS)同时测定尿样中硒及铬、镉、砷、铅、锰、钴、镍、铜、锌10种重金属元素的方法。采用硝酸-过氧化氢消解体系,微波消解法制备样品.以铟、铋为内标物质,直接用ICP-MS测定上述10种元素。所测10种元素的检出限为0.006-0.073μg/L,校准曲线线性关系好(r>0.9999),相对标准偏差(RSD)均小于3%,对尿样标准物质的测定值均在标准参考值范围内。应用微波消解ICP-MS分析尿样,方便快捷,灵敏度高,检出限低,重现性好,是理想的生物样本检删分析方法。     

Investigating the impact of internal standard heterogeneity on gold quantification with total reflection X-ray fluorescence: A simulation study

Total reflection X-ray Fluorescence (TXRF) is a powerful analytical tool with high detection sensitivity that has been applied to a variety of biological samples. While its ability to quantify gold nanoparticles (AuNPs) in cancer cells has been demonstrated, the extension to tissue slices would be of interest. To that end, the preservation of the underlying tissue microstructure requires samples to be measured as microtome slices. In this form, internal standard spiking is warranted. Thus, it is important to examine the impact of sample heterogeneity on the TXRF's quantification accuracy. To address these questions, a TXRF spectrometer along with 5 μm thin heterogeneous and homogeneous samples were modeled using TOPAS. The simulation model generated TXRF spectra which were then analyzed to obtain recovery rates of Au in both sample types. The results showed near 100% recovery regardless of the elemental spatial distribution in the samples. This provides insights into the quantification potential for AuNPs inside tumors that are histologically processed into thin tissue slices. In addition, this simulation toolkit provides the first practical means of modeling TXRF spectroscopy which will hopefully be of use to the TXRF community.     

Carbon Nanotube/P(VDF-TrFE) Nano-Composite Characterization by Total Reflection X-Ray Fluorescence

In continuation of our research on carbon nanotube/P(VDF-TrFE) nano-composites [1], total x-ray fluorescence (TXRF) is engaged in a novel characterization of these materials regarding their compositions, purities, and structural analysis. Samples such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), P(VDF-TrFE) copolymer, SWCNT/P(VDF-TrFE), and MWCNT/P(VDF-TrFE) were analyzed by TXRF. The synthetic quartz used as a substrate was analyzed as reference material for the TXRF measurements. The ethanol and the dimethylformamide (DMF) used as solvents for carbon nanotubes and copolymers respectively were also analyzed by TXRF to determine whether they have an influence or not on the TXRF of the previous material. The preliminary results showed that single-walled and multi-walled carbon nanotubes prepared by the arc-discharge method contain catalytic particles such as Fe, Co, and Ni used to obtain SWCNT while there were no metal or impurities in MWCNT. The TXRF spectrum of CNT/P(VDFTrFE) showed the same results as we found previously with background due to the P(VDF-TrFE) copolymer scattered signal. __________ Published in Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 700–702, September–October, 2005.     

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.     

Lead Fractionation Analysis in Lipstick Samples by Inductively Coupled Plasma-Mass Spectrometry

A new analytical approach based on fractionation was introduced for lead in lipstick samples. Different separation techniques including n-hexane, glycerol extraction, and activated carbon adsorption were used to characterize the lipid fraction, polar and aromatic components of the samples. Additionally, artificial saliva and food stimulant extractions were used for the risk assessment studies. Trace metal levels in fractions were determined by inductively coupled plasma-mass spectrometry. Method validation parameters in the total element determinations were defined in terms of detection limits, accuracy, and precision. The limits of detection and quantification were 0.02 and 0.07 mg kg^?1 for Pb; whereas the repeatability and reproducibility of the results based on percent relative standard deviation were 3.0% and 7.2% for lead, respectively.     

Patterns of inter‐elemental effects in EDXRF and a new correction method

A new method is suggested for improving the accuracy of energy‐dispersive x‐ray fluorescence analysis (EDXRF) and its implementation is described. This method is a result of studying changes in coefficients of the inter‐elemental effect, A = f(Z). We created a data bank for elements from K to Br, which accounts for the effect of three lighter and five heavier neighboring elements upon the sought element. This study offers a physical explanation of sharp bends in coefficient curves. We suggest principles for optimizing the analytical region parameters so as to reduce the effect of neighboring elements. Finally, we describe the principles of building a data bank A = f(Z, R) to account for the effect of energy resolution (R) change. Application of the suggested method to the exploration of oceanic nodules reduced the cobalt detection threshold by 50–75% (C_lim?0.95 = 0.032%) and decreased the standard deviation of spectrum analysis, thus enhancing confidence in EDXRF as an effective tool for research on complex objects. The approach suggested in this study can be used with newer energy‐dispersive analyzers, including TXRF models. Copyright © 2003 John Wiley & Sons, Ltd.     

高压消解-紫外分光光度法测定红花中的重金属

采用高压消解-紫外分光光度法,建立了测定淮红花中的重金属含量的方法。结果表明:此法铅含量在0—40μg范围内,与吸光度线性关系良好,r=0.9989。淮红花中重金属含量为18.71μg/g,符合国家标准,平均加标回收率为97.82%,RSD=2.93%(n=5)。高压消解法的使用,进一步提高了测定方法的准确性和便捷性,此法可用于中药中重金属含量的检测。