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.     

Application of high‐energy polarized energy‐dispersive x‐ray fluorescence spectrometry to the determination of trace levels of As,Hg, and Pb in certifiable color additives

Advances in x‐ray fluorescence (XRF) using high‐energy polarized energy‐dispersive (ED)XRF spectrometry (PEDXRF) were applied to the determination of trace As, Hg, and Pb in various color additives subject to batch certification by the U.S. Food and Drug Administration (FDA). The objectives of this study were to simplify sample preparation for quantitative determination of these elements and, if possible, to achieve improved sensitivity and detection limits compared to techniques currently used for certification. PEDXRF was compared with wavelength‐dispersive x‐ray fluorescence spectrometry (WDXRF) and inductively coupled plasma – mass spectrometry (ICP‐MS) for the analysis of trace levels of As, Hg, and Pb in certifiable color additives. For these light matrices, PEDXRF provided better signal‐to‐noise and allowed quantitation in smaller amounts of color additive relative to WDXRF and equal or better precision to ICP‐MS. Determination of these trace elements in a variety of color additives was possible relative to calibrations generated from one color additive using specimens prepared simply by pouring the color additive powder into an XRF sample cup. Published 2016. This article is a U.S. Government work and is in the public domain in the USA     

Improvement of a TXRF setup to obtain detection limit in the low ppb range

To achieve the low ppb detection level a major experimental effort and optimization of the TXRF setup are required. The new solution described in this paper leads to enhancement of the TXRF intensity and to improved signal/noise ratio. The adjusted quartz reflector allows control of a reflection angle of a photon beam with respect to the crystal surface with high precision up to 0.006°. The installed adjusted diaphragm (followed by the quartz reflector) substantially reduces the level of registered background in the studied range of x‐ray energy. The dependence of the x‐ray spectra shape, x‐ray intensity and detection limit on the diaphragm width and its position on the photon beam as well as on the value of the glancing angle of x‐rays from the sample carrier have been studied. The new optimal parameters found result in essential improvement in detection limit equal to ～1.0 ppb for elements detected in a liquid sample without any special pre‐concentration preparation. Also a very good repeatability of measurements has been reached. Copyright © 2006 John Wiley & Sons, Ltd.     

A sample carrier for measuring discrete powdered samples with an ITRAX XRF core scanner

The elemental composition of discrete powdered sediment samples can be measured by the energy‐dispersive X‐ray fluorescence (XRF) system that is installed in XRF core scanners. Because an appropriate sample carrier for powdered samples is currently not available, for example, for the ITRAX XRF core scanner, such a carrier is presented in this technical note. The designed sample carrier can hold 30 sample cups with a volume of 0.88 cm³ each. A maximum of 5 sample carriers, that is, 150 samples, can be measured in one run. The sample cups and carriers are optimized for a measurement procedure with a step size of 5 mm and variable count times up to 100 s per sample. With this setting, data are collected from an area of 100 mm² in the center of the sample thereby ensuring a good representativeness of the signal because potential sample inhomogeneity is accounted for. Because the described sample carrier system allows rapid element analyses of discrete powdered environmental samples with an XRF core scanner, it may in some cases represent a time‐ and cost‐efficient alternative to conventional XRF analyses.     

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.     

Analytical performance of Compton/Rayleigh signal ratio by total reflection X-ray fluorescence (TXRF): A potential methodological tool for sample differentiation

The high sensitivity Compton and Rayleigh X-ray scattering signals can be used to gain valuable information on the chemical composition of various matrices, by exploiting the ratio of those signals as a function of the effective atomic number (Z_eff). Neither total reflection X-ray fluorescence (TXRF) nor the effect of the experimental setup, including sample preparation, X-ray excitation source selection, and band deconvolution procedure, has been assessed in this kind of approach. Here, a Compton/Rayleigh ratio and Z_eff-based TXRF method was set up and tested as an analytical tool for milk samples differentiation. The method was developed using a 90° scattering angle and assessed using different X-ray excitation sources: a molybdenum tube (Mo Kα 17.5 KeV) and a tungsten tube (W Lα 8.5 KeV and W-Brems 35 KeV). The evaluation of independent Compton and Rayleigh signals was performed by non-Gaussian and Gaussian curve resolution methods, and both height and area-based calculations were evaluated. Different sample preparation conditions were assessed. By using 11 standard materials, a calibration curve for Compton/Rayleigh ratio versus Z_eff was established. The method was tested to determine the Z_eff of milk samples, which enabled its use as a parameter to differentiate them. Good precisions were obtained with the Mo excitation source and the area-based calculations, which allowed to differentiate undiluted milk samples by species, treatment, and fat content according to their Compton/Rayleigh ratio. This simple and rapid method has the potential to be used for the differentiation of various types of samples, including liquids, solids, and aerosols.     

Characterization of x‐rays emerging from between reflector and sample carrier in reflector‐assisted TXRF analysis

The possible application of an Si reflector, which is placed just above the sample carrier in total reflection x‐ray fluorescence (TXRF) analysis, was investigated. The x‐rays that were emitted from an Mo tube and passed between the Si reflector and the Si sample carrier were analyzed with an Si drift detector. In our experimental setup, the angle between the reflector and the sample carrier can be changed by adjusting the inclination of the reflector. The intensity of the x‐rays that emerged from between the two Si surfaces drastically changed depending on the reflector angle. At a proper reflector angle, this intensity showed a maximum and, in addition, the Compton peak in the x‐ray spectrum was suppressed. When this x‐ray beam was used for excitation of TXRF signals, the highest intensity of x‐ray fluorescence emitted from the sample was detected, indicating that these experimental conditions are useful for the enhancement of TXRF intensities. Copyright © 2004 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.     

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.     

Total reflection x‐ray fluorescence analysis—a review

Total reflection x‐ray fluorescence analysis (TXRF) is a special energy‐dispersive x‐ray analytical technique extending XRF down to the ultra trace element range. Detection limits of picograms or nanograms per gram levels are reached with x‐ray tube excitation. Using synchrotron radiation as excitation source, femtogram levels are detectable, particularly important for Si wafer surface analysis. TXRF is specially suited for applications in which only a very small amount of sample is available, as only a few micrograms are required for the analysis. In this review, an overview of theoretical principles, advantages, instrumentation, quantification and application is given. Chemical analysis as well as surface analysis including depth profiling and thin‐film characterization is described. Special research results on extension to low‐Z elements, excitation with synchrotron radiation and x‐ray absorption spectroscopy (XAS) for chemical speciation at trace levels are reviewed. Copyright © 2007 John Wiley & Sons, Ltd.     

Direct chemical characterisation of clay suspensions by WD‐XRF

This study was performed to develop a method for directly controlling the chemical composition of clay slurries used in preparing ceramic floor and wall tile bodies by wavelength‐dispersive X‐ray fluorescence (WD‐XRF) spectrometry, without the prior need to dry and prepare the samples as fused beads or pellets for WD‐XRF measurement, owing to the importance of knowing the suspension chemical composition in real time for appropriate control of the industrial process. The study was conducted on a wide range of ceramic floor and wall tile bodies, which are used to prepare different suspensions. The influence of suspension viscosity (from 300 to 7000 cp), of suspension solids content (between 66 and 69%), and of the type of body composition (floor or wall tile) on the WD‐XRF measurement was determined. In these viscosity and solid content ranges, no appreciable differences were observed in the WD‐XRF measurement results, indicating that the possibly arising variations in viscosity and solids content in such clay suspensions in industrial practice do not influence the WD‐XRF measurement. In contrast, the type of body composition did influence the WD‐XRF measurement. The developed method is rapid, reproducible, and accurate, which was verified by analysis of the materials using the customary method of WD‐XRF measurement on fused beads. In addition, this method is cheaper and more harmless to the environment; it minimises waste generation, since no sample preparation is required and the plastic sample holders can be reused, thanks to the reusable sample holder system designed at the Instituto de Tecnología Cerámica laboratories. Copyright © 2011 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.     

XRF spectrometer calibration for copper determination in wood

Method of X‐ray fluorescence (XRF) spectrometer calibration for copper analysis in wood was elaborated. Copper salt standard solutions for XRF measurements of liquid samples were prepared, and calibration curve of copper content dependence on impulse counts was determined. Specimens of pine wood (Pinus sylvestris L.) were treated with different solutions of copper‐based preservative (alkaline copper quarternary ammonium compound type) applying model low‐pressure preservation process. After treatment, wood specimens were sliced into six pieces, and exposed surfaces were analyzed using mapping option of XRF spectrometer. Then, wood from each analyzed surface was peeled with abrasive paper and dissolved in 65% nitric (V) acid. Copper content in solutions was determined using obtained calibration curve, and calibration dependence of copper content in wood on the average impulse counts on particular surfaces was calculated. Obtained results of copper content were consistent with values calculated on the basis of differences of samples weight before and after treatment. It confirms that proposed procedure is correct, and obtained equation may be used for unknown samples examination. Copyright © 2012 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.     

Analytical Study of Raw Materials of Zinc Oxide Used for Enamels on Industrial Ceramics: Quantitative Analysis of Zinc,Lead, and Sulfur in These Samples by X‐ray Fluorescence and Flame Atomic Absorption Spectrometry

An analytical study is carried out to optimize X‐ray fluorescence (XRF) and flame atomic absorption spectrometry (FAAS) quantitative analysis of Zn, Pb, and S in ZnO samples commonly used to obtain industrial ceramic enamels. Pb and S in the raw materials often contaminate ZnO and are very detrimental in industrial applications. Thus, very accurate analytical determination of these elements in ceramic samples is extremely important. First of all, a mineralogical study by X‐ray diffraction (XRD) on the different components in these raw materials and the materials produced during the firing process is performed in order to establish the mineral forms in a reference sample for analysis by XRF spectrometry. The working conditions are optimized for XRF multielemental analysis, using the sample in the form of pellets, due to high loss on ignition (LOI) values. The preparation of suitable standards and working conditions for FAAS analysis have also been optimized. The content of these elements was determined by FAAS for the reference sample and several samples for industrial use, and the results were compared with those obtained by XRF. Comparison of the results obtained from XRF and FAAS analysis of Pb and Zn show more accurate values for FAAS. For ZnO, an accuracy of 0.11% with ±0.1% precision by FAAS and 0.46% accuracy with ±0.2% precision by XRF are found. For PbO, 1.06% accuracy and ±0.06% precision using FAAS and 5.6% accuracy and ±0.35% precision by XRF were found. For SO₃ determined only by XRF, accuracy was 4.76% with ±0.25% precision. These values are highly satisfactory given that these two elements are only found in small proportions.     

Fourier‐transform Raman analysis of milk powder: a potential method for rapid quality screening

In this work, FT‐Raman spectroscopy was explored as a fast and reliable screening method for the assessment of milk powder quality and the identification of samples adulterated with whey (1–40% w/w). Raman measurements can easily differentiate milk powders without the need of sample preparation, whereas the traditional methods of quality control, including high‐performance liquid chromatography, are laborious and slow. The FT‐Raman spectra of whole, low‐fat, and skimmed milk powder samples were obtained and distinguished from commercial milk powder samples. In addition, the exploratory analysis employing data from Raman spectroscopy and principal component analysis (PCA)allowed the separation of milk powder samples according to type,identifying differences between samples in the same group. Multivariate analysis was also developed to classify the adulterated milk powder samples using PCA and partial least squares discriminate analysis (PLS‐DA). The resulting PLS‐DA model correctly classified 100% of the adulterated samples. These results clearly demonstrate the utility of FT‐Raman spectroscopy combined with chemometrics as a rapid method for screening milk powder. Copyright © 2011 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.     

全反射X射线荧光分析植物粉末样品的制样方法研究

全反射X射线荧光光谱(TXRF)分析是一种应用广泛、经济快捷的多元素显微与痕量分析方法。随着现代科技机器自动化的快速发展,样品制备成为TXRF分析定量的关键问题。本实验以茶叶粉末为分析对象,探讨了在TXRF分析过程中分散剂、样品量及粒径对粉末悬浮样品的制样效果、制样过程重复性及测量准确性的影响。结果表明：（1）通过分析粒径范围大于180目的茶叶粉末样品的五个独立重复试样,测试了TXRF法的整体精密度,分析了仪器的稳定性与样品制备过程中的不确定度,结果表明不论在何种元素与浓度范围下,与样品制备步骤相关的不确定度对获得的结果的全局精度都有显著贡献（>60%）,样品的制备是分析误差的主要来源;（2）通过将粒径范围大于180目的茶叶粉末样品分散于1% Triton X-100与去离子水两种分散剂中,对分散剂的影响进行了研究,相较于非离子型表面活性剂,去离子水重复性更好,RSD在2.45%～11.64%之间,更适合作为粒径大于180目的茶叶粉末样品的分散剂,使得中、高Z元素的定量更为准确;（3）通过添加不同质量的粉末样品于5 mL去离子水中对样品量进行分析。样品量过低会导致制样重复性较差,而过高的进样量会导致样品薄膜厚度超过射线的测量厚度,有可能不再处于全反射条件下。对于植物粉末样品20 mg/5 mL是一个较为合适的样品量;（4）通过对7种粒径范围的粉末样品进行测量分析,研究了粒径对测量结果的影响。在粒径小于180目的范围内净计数随粒径的减小而增大;在粒径小于200目的范围内精密度随粒径的减小而提升;除Mn之外的元素粒径对准确性未有显著影响;在80～200目的范围内,不确定度迅速降低,大于200目后不确定度低于10%。综合考虑净计数、精密性与准确性,在制样过程中粒径范围建议研磨至200～300目之间,该研究结果可为植物粉末样品制样方法提供有效借鉴。     

Random left‐censoring: a statistical approach accounting for detection limits in x‐ray fluorescence analysis

The use of x‐ray fluorescence techniques (XRF, TXRF, µXRF) in studies of trace element concentrations is limited by the detection limits (DL) of these methods. In this work we demonstrate that concentration measurements below the DL level, the so‐called ‘non‐detects’, can be included in data analysis by using the statistical concept of ‘censoring’, which is widely used, for instance, in survival analysis. This paper describes the non‐parametric methods of analysis of censored data using the random left‐censoring formalism, which can be used to account for the detection limits in XRF analysis. In particular, the application of the Kaplan–Meier and Nelson–Aalen estimators for the estimation of concentration distributions under censoring is discussed. These approaches are compared with the ‘reconstruction method’ developed earlier in our group to correct XRF data for the effect of detection limits. By using Monte Carlo simulations, the accuracy of the Kaplan–Meier and Nelson–Aalen estimators for censored data is discussed, in particular in the context of the estimation of the mean value and median of a concentration distribution. We demonstrate that for the ‘two‐group’ comparison of left‐censored concentrations, which is a problem of great practical importance, the log‐rank test can be used. The idea of random left censoring is applied to analyse the TXRF detection limit‐censored measurements of the concentrations of trace elements in biomedical samples. Copyright © 2004 John Wiley & Sons, Ltd.     

Recent Advances in TXRF

Abstract

Total reflection X‐ray fluorescence analysis (TXRF) is a special method of energy‐dispersive X‐ray fluorescence analysis extending EDXRF to the ultra trace element level. The achievable detection limits depend on the excitation source and are in the range of picograms to femtograms. Only small amounts of sample are required and the quantification by adding one element as an internal standard is easy as thin film approximation is valid. In this article, the recent advances in TXRF are reviewed with over 80 references. The principles, advantages, instrumentation, improvements with X‐ray optics, synchrotron radiation as excitation sources as well as various fields of application, wafer surface analysis, depth profiling, absorption spectroscopy, medical samples, biological samples, environmental monitoring, archeological and polymer samples are described. Related techniques are also mentioned and discussed.