Fundamental Parameter Approach Research Articles

Data quality in laboratory convergent-beam X-ray total scattering

Measurement of laboratory atomic pair distribution function data has improved with contemporary X-ray sources, optics and detectors, with acquisition times of the order of minutes for ideal samples. This paper examines resolution effects in pair distribution function data obtained using a convergent-beam configuration and an Ag X-ray tube from standard silicon powder and from 10 nm BaTiO3 nanocubes. The elliptical multilayer X-ray mirror reflects a non-trivial X-ray spectrum and introduces resolution effects not commonly treated in ordinary parafocusing divergent-beam laboratory diffraction. These resolution effects are modeled using the fundamental parameters approach, and the influence this has on interpretation and modeling of the resulting reduced atomic pair distribution function data is demonstrated.

X-ray fluorescence spectroscopy (XRF) for metallome analysis of herbarium specimens

Background“Herbarium X-ray Fluorescence (XRF) Ionomics” is a new quantitative approach for extracting the elemental concentrations from herbarium specimens using handheld XRF devices. These instruments are principally designed for dense sample material of infinite thickness (such as rock or soil powder), and their built-in algorithms and factory calibrations perform poorly on the thin dry plant leaves encountered in herbaria. While empirical calibrations have been used for ‘correcting’ measured XRF values post hoc, this approach has major shortcomings. As such, a universal independent data analysis pipeline permitting full control and transparency throughout the quantification process is highly desirable. Here we have developed such a pipeline based on Dynamic Analysis as implemented in the GeoPIXE package, employing a Fundamental Parameters approach requiring only a description of the measurement hardware and derivation of the sample areal density, based on a universal standard.ResultsThe new pipeline was tested on potassium, calcium, manganese, iron, cobalt, nickel, and zinc concentrations in dry plant leaves. The Dynamic Analysis method can correct for complex X-ray interactions and performs better than both the built-in instrument algorithms and the empirical calibration approach. The new pipeline is also able to identify and quantify elements that are not detected and reported by the device built-in algorithms and provides good estimates of elemental concentrations where empirical calibrations are not straightforward.ConclusionsThe new pipeline for processing XRF data of herbarium specimens has a greater accuracy and is more robust than the device built-in algorithms and empirical calibrations. It also gives access to all elements detected in the XRF spectrum. The new analysis pipeline has made Herbarium XRF approach even more powerful to study the metallome of existing plant collections.

Comparative Study of Heavy Metals Analysis in Mongolian Medicines Based on High Sensitivity X-ray Fluorescence Spectroscopy and ICP-MS

The contents of Pb, Hg, As, Cr, Fe, Cu, Ba, and Cd in five traditional Mongolian medicines (Garidi-5, Susi-7, Yihe-12, Zadi- 5, and Alatanaru-5) were determined by X-ray fluorescence (XRF) spectroscopy. The results were compared with those obtained by inductively coupled plasma–mass spectrometry (ICP-MS). According to the fundamental parameter (FP) approach in XRF, the response signal value was converted into the element content value using computer software. The method was stable and fast, not requiring pretreatment processes. When the content of metal elements was below 2.0 mg/kg, the relative standard deviation (RSD) of the precision test was between 5.49–20.0%. When the content was above 2.0 mg/kg, the RSD of the precision test was less than 4.96%. The limits of quantitation (LOQ) of As, Cd, and Pb were all below 0.1 ppm, the limits of quantitation of Cr, Cu, Ba, and Hg were below 1 ppm, and the limit of quantitation of Fe was 1.525 ppm. The standard addition method was used in the accuracy test, and the recoveries of the other seven elements were all within 85–130% except Hg. Because Hg was easy to volatilize, the recoveries were low but above 68.4%.

Determination of physically based pseudo-Voigt powder diffraction profile terms from the fundamental parameters approach

A methodology is developed where a fundamental parameters approach (FPA) description of a laboratory powder diffraction instrument (configured in divergent-beam Bragg–Brentano geometry) is used to determine GSAS-II profile parameters for peak asymmetry and instrumental peak widths. This allows the instrumental contribution to peak shapes to be robustly determined directly from a physical description of the instrument, even though GSAS-II does not directly implement FPA for peak shape computation. The FPA-derived parameters can be used as the starting point for instrument characterization, or to characterize sample broadening without the use of a standard to determine the instrument profile function. This new method can facilitate generation of training sets for machine learning. A plot is generated that shows the differences between the two approaches, demonstrating upper bounds for the accuracy of the GSAS-II profile model for a particular instrumental configuration.

Analysis of human tissues using Energy Dispersive X Ray Fluorescence – Dark matrix determination for the application to cancer research

BackgroundX ray Fluorescence has been essayed as a suitable technique for the elemental quantification of trace element in human tissues, namely comparison of normal and cancerous tissue. However, accurate results depend on a robust quantification approach, namely correct evaluation of the samples’ dark matrix. MethodsIn order to determine the most suitable dark matrix composition for the quantification of such samples using the Fundamental Parameter approach, we have measured several Certified Reference Materials and essayed different dark matrix compositions to achieve the most accurate results. The resulting dark matrix was then applied to normal and tumor ovarian and prostate tissue samples, and the obtained results were compared with the ones obtained with a comparative method using external standard calibration curves. ResultsUsing a dark matrix composed of 10 % - H, 22 % - C, 3 % - N and 60 % - O yielded the best compromise in accuracy for the light and heavy elements. For the reduced sample size and conditions of this study, for both organs, the concentrations of transition metals decrease in tumor tissues, while the concentration of lighter elements, P and Cl, increases. On the other hand, there are elements that showed different behavior between the two types of tissue, namely Zn and S, that increase in prostate tumor tissue and decrease in ovarian tissue. ConclusionAn increase in precision was one of the improvements found with the newly developed method, as the FP-approach contemplates matrix effects and the influence of other elements in the analytes’ quantification. Additionally, the determined dark matrix can be employed in any tissue analysis application by means of EDXRF.

Rapid elemental composition analysis of spinach samples employing wavelength dispersive X-ray fluorescence spectroscopy

The increasing demand to carry out nondestructive analysis with minimal sample preparation for the detection of chlorine element in the spinach samples requires advanced analytical techniques with better energy resolution. The emergence of wavelength dispersive X-ray fluorescence instruments offers new chances for fast and inexpensive plant leaf analysis, both as laboratory and in-situ-based systems. Earlier efforts to use X-ray fluorescence analyses for various plant samples, especially spinach leaves, were limited by the large background caused by scattering of the primary X-ray source which has been overcome by using the commercial wavelength dispersive technique. It is a potential influential research tool for the study of trace elemental composition analysis under different analytical parameters and simple sample preparation protocols. In the present work, the chlorine content ∼0.8% has been measured in the spinach leaf standard reference material (SRM 1570a) from the National Institute of Standards and Technology, USA by using the wavelength dispersive X-ray fluorescence technique employing a fundamental parameter approach. Keeping in view the importance of the knowledge about the chlorine content in plant leaf samples and the reliability of the methodology used in the present work to determine chlorine content, it is recommended that the present measured chlorin.e concentration be included in the datasheet of certified values by the National Institute of Standards and Technology, the USA for effective use of this standard reference material.

X-ray fluorescence analysis of major and trace elements in silicate rocks using 1:5 dilution glass beads

Thisreport describes analytical techniques for major and trace elements in silicate rocks by X-ray fluorescence (XRF) spectrometry. The analyzed elements are SiOz, Ti02, A1203, total Fe203, MnO, MgO, CaO, Na20, K20, P2Os, Sc, V, Cr, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Nd and Pb. All of these elements were determined on a single glass bead made from mixtures of 1 g of sample powder, 5 g of Li2B407 flux and about 50 mg of Lil releasing agent. A series of synthetic standard samples were prepared from pure chemical reagents to calibrate an XRF spectrometer. Matrix and line overlap corrections using a fundamental parameter approach yields reliable calibration lines with wide optimal ranges of composition. Analytical results of GSJ geochemical reference samples are in good agreement with their recommended values and exhibit sufficient precision and sensitivity for both major and trace elements.

Phase Equilibria of the MnTe-Sb2Te3 System and Synthesis of Novel Ternary Layered Compound – MnSb4Te7

By using Differential Thermal Analysis (DTA) and Powder X-ray Diffraction (PXRD) techniques, the phase diagram of the MnTe-Sb2Te3 system has been constructed for the first time in the entire composition range. The system features two ternary layered van der Waals (vdW) compounds. Apart from known MnSb2Te4, novel MnSb4Te7 which a structural analogous of the known MnBi4Te7 was found in the system. Crystal structure parameters of both compounds were determined by Rietveld refinement using the fundamental parameter approach. Both compounds were found to decompose via peritectic reactions and possess significant homogeneity ranges. The title system is also characterized by the existence of the wide solid solution field based on the starting Sb2Te3. The present results would be useful for the bulk single crystal growth of both compounds from the liquid phase via the determination of primary crystallization areas.

Analysis of phosphorous content in cancer tissue by synchrotron micro-XRF

In the present work, an analytical procedure for spatial quantification of phosphorous in cancerous tissues by micro-XRF was developed. This new methodology based on fundamental parameter approach consists of evaluating the incoming microbeam excitation x-ray spectrum on the sample and the matrix effects. The former was determined through a spectral reconstruction technique, based on the scattering pattern of a thin standard plastic material and the latter with the assistance of two transmission monitor ionization chambers. The procedure was applied on fifteen samples of murine gland mammary adenocarcinoma fixed in paraffin. Slices of 30 μm of these samples were scanned at air atmosphere in areas of 5 mm × 5 mm with a spatial resolution of 20 μm. The acquisition time per pixel was 5s allowing a detection limit for phosphorous of 240 ppm w/w. The results showed that the technique is able to detect the elevation of the phosphorous content in tumour tissues, as it was previously reported in the literature using other techniques. In addition, the spatial resolution of the technique allowed associating this increment with areas composed mainly by active tumour cells that were previously identified by Haematoxylin staining. In these areas, phosphorous concentrations showed spatial variations probably associated with tumour metabolism. Thus, micro-XRF offers valuable information of P spatial distribution that could be useful to identify active tumour cells as well as to study of tumour growth and progression.

The Certification of Standard Reference Material 1979: Powder Diffraction Line Profile Standard for Crystallite Size Analysis.

This rather long-standing project has resulted in a National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) for the analysis of crystallite size from a consideration of powder diffraction line profile broadening. It consists of two zinc oxide powders, one with a crystallite size distribution centered at approximately 15 nm, and a second centered at about 60 nm. These materials display the effects of stacking faults that broaden specific hkl reflections and a slight amount of microstrain broadening. Certification data were collected on the high-resolution powder diffractometer located at beamline 11-BM of the Advanced Photon Source, and on a NIST-built laboratory diffractometer equipped with a Johansson incident beam monochromator and position sensitive detector. Fourier transforms were extracted from the raw data using a modified, two-step profile fitting procedure that addressed the issue of accurate background determination. The mean column lengths, 〈L〉area and 〈L〉vol, were then computed from the Fourier transforms of the specimen contribution for each reflection. Data were also analyzed with fundamental parameters approach refinements using broadening models to yield 〈L〉area and 〈L〉vol values. These values were consistent with the model-independent Fourier transform results; however, small discrepancies were noted for the 〈L〉area values from both machines and both crystallite size ranges. The fundamental parameters approach fits to the laboratory data yielded the certified lattice parameters.

Application of fundamental parameter approach using integrated backscattering intensity for X-ray fluorescence analysis

The fundamental parameter (FP) approach, in which the both intensities of coherently (Rayleigh) and incoherently (Compton) scattered primary radiation are added individually to estimate the ‘dark matrix’ of the analyzed specimen, is considered successful, especially for in situ element determination. However, the current energy resolution of the energy-dispersive X-ray fluorescence (EDXRF) spectrometer system is not yet high enough for two scattered peaks to appear without overlapping in general, and separating two peaks with each other yields reduced accuracy of analysis. The FP approach with only the integrated backscattering intensity added in place of both of the individual backscatter intensities is proposed for X-ray fluorescence (XRF) analysis of unknown specimen. The present results show that the weight fraction deviations are below 5%, which is much lower than the maximum error 10.79% of the results for four selected samples by using the previous BFP. Our determination of elements reveals Na, Mg, Al, and Si as hypothetical elements representing compositions SiO2 and Al2O3, namely the main compositions of the gangue for the geological samples as a mineral ore.

Evaluation of X‐Ray Fluorescence Spectroscopy as a Tool for Nutrient Analysis of Pea Seeds

ABSTRACTThis research was conducted to evaluate the utility and reliability of X‐ray fluorescence (XRF) spectroscopy to analyze macro‐ (K and Ca) and micronutrients (Mn, Fe, Cu, Zn, and Se) in pea (Pisum sativum L.) seeds. The pea seed samples were ground into flour and pelleted to collect the XRF spectra. Seventy‐three pea seed samples were selected to cover the expected concentration ranges for each element to develop calibration curves by correlating the XRF results with atomic absorption spectroscopy (AAS). The XRF results were validated by a systematic comparison of data obtained from AAS on a set of 80 additional and independent pea seed samples. Element concentrations were also predicted using the fundamental parameter approach collectively for 153 samples. For all the calibration curves, the R2 value was >0.8, except for K (0.54). For Mn, Fe, Cu, Zn, and Se, the XRF predictions were similar to AAS measurements at a 95% confidence level. Similar results were obtained with the fundamental parameter approach except for Fe for which significant bias of ∼6 mg kg−1 was calculated. Except for K, R value for all the validation curves was >0.85. Thus, the results obtained using XRF and the fundamental parameter approach were statistically not different from the AAS method. This study demonstrated that the XRF technique is a fast and reliable, nondestructive, and noninvasive analytical tool for mineral analysis, particularly for transition metals, does not produce waste, and requires no chemical reagents.

The optics of focusing bent-crystal monochromators on X-ray powder diffractometers with application to lattice parameter determination and microstructure analysis.

The use of an Incident Beam Monochromator (IBM) in an X-ray powder diffractometer modifies both the shape of the spectrum from the X-ray source, and the relation between the apparent diffracted angle and the actual wavelength of the X-ray. For high-accuracy work, the traditional assumption of a narrow line of typically Gaussian shape does not suffice. Both the shape of the tails of peaks, and their width, can be described by a new model which couples the dispersion from the optic to the dispersion from the powder sample, and to its transport to a detector. This work presents such a model, and demonstrates that it produces excellent fits via the Fundamental Parameter Approach, and requires few free parameters to achieve this. Further, the parameters used are directly relatable to physical characteristics of the diffractometer optics. This agreement is critical for the evaluation of high-precision lattice parameters and crystal microstructural parameters by powder diffraction.

Applicability of Low-Cost Binders for the Quantitative Elemental Analysis of Urinary Stones Using EDXRF Based on Fundamental Parameter Approach.

The pressed powder sample is a common method for elemental analysis using X-ray fluorescence analysis whereas suitable light hydrocarbon materials should be added to the sample as a binder. The present study demonstrates the applicability of using different commercial binders for elemental analysis of urinary stone samples. In order to confirm the obtained results, a comparison with pure chemical grade binders was presented. Different commercial and pure binders were tested for quantitative elemental analysis of urinary stones, namely, cellulose, starch, wax, and urea. Energy dispersive X-ray fluorescence (EDXRF) was used for elemental analysis. Differential thermal analysis was used to estimate the loss on ignition (LOI) in the urinary stone samples. The signal to background ratios (I/IB) of the different detected elements in the commercial and pure binders were calculated, compared, and studied at eight different photon energies starting from 2.5 up to 37keV. Standard-less quantitative analysis method based on the fundamental parameter approach was applied for elemental analysis of selected urinary stones. The commercial and low-cost binders could be an excellent alternative binder for urinary stone analysis using energy dispersive X-ray fluorescence. The commercial binders could provide an advantage as pure chemical grade binders or even better especially at photon energy higher than 10keV. The best commercial binder candidate was found to be the wax. The quantitative analysis results using commercial and pure chemical grade binders give good agreement results, which indicate the applicability of commercial binders for quantitative elemental analysis of urinary stones in the form of pressed powder samples.

Analysis of Elemental Composition of Fe1−xNix and Si1−xGex Alloy Thin Films by EPMA and μ-XRF

The present study reports on measurements on thin Fe-Ni films on silicon and first-time results of analysis on Si-Ge thin films deposited on a non-conductive aluminium oxide Substrate by electron probe microanalysis (EPMA). Standard-based and standardless EPMA (with EDS) results were used in combination with the thin film analysis software Stratagem for the quantification. Further, X-ray fluorescence analysis (XRF) can be used for the determination of elemental composition and thickness of such films as well. In this case, XRF with a μ-focus X-ray source (μ-XRF) attached to a SEM was applied. For quantification, a fundamental parameter (FP) approach has been used to calculate standard-based and standardless results. Both thin film systems have been chosen as samples of an international round robin test (RRT) organised in the frame of standardisation technical committee ISO/TC 201 ‘Surface chemical analysis’, under the lead of KRISS. The main objective of the RRT is to compare the results of atomic fractions of Fe1-xNix and Si1-xGex alloy films obtained by different surface Analysis techniques, such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) applied in the depth-profiling operation mode. Five samples of different atomic fractions of each thin film system, i.e., Fe1-xNix and Si1-xGex, have been grown by ion beam sputter deposition on silicon and Al2O3 wafers, respectively. Reference FeNi and SiGe films with well-known elemental composition and thickness have been also supplied for standard-based analysis. An excellent agreement has been obtained between the atomic fractions determined by EPMA and µ-XRF with the KRISS certified values.zeige mehr

A re-examination of the fundamental parameters approach to calibration of the Curiosity rover alpha particle X-ray spectrometer

In terrestrial instruments for X-ray emission analysis (e.g. X-ray fluorescence, electron microprobe) the angle of excitation and the angle of characteristic X-ray emission by samples are typically well-defined. This is not the case for the Mars rovers’ alpha particle X-ray spectrometers, necessitating use of “effective” angles in any fundamental parameters approach to spectrum fitting and derivation of element concentrations. A new Monte Carlo computation of expected characteristic X-ray yields has enabled us to examine the choice of effective angles in detail and to compare with our previous estimates; the mean angles taken over all detected events appear to be the most satisfactory approximation. These were used in our GUAPX code to process APXS spectra from ten mono-mineralic geochemical reference materials. Agreement between our concentration values and those determined by the specialist company ActLabs was excellent.

Spatial distribution of Si in Pinus Insigne (Pinus radiata) Wood using micro XRF by Synchrotron Radiation

Silicon, while not an essential element, is known to have positive roles in certain vegetable species. For instance, it has been recognized to protect them from biotic and abiotic stress. Due to the fact that certain species accumulate the aforementioned element in their tissues, the determination of its concentration is of importance in different disciplines, such as dendrology, plant physiology, forest management, agroecology, and also in the wood industry. Usually, its quantification is preceded by a series of digestion steps that, aside from been time-consuming, and contamination-prone, prevents from conducting a spatial distribution of the element on the sample. In this research, samples of Pinus radiata wood were studied using a synchrotron radiation source that allowed direct scanning of its surface without any treatment, and the determination of silicon as a function of the position and the tree rings, using micro X-ray fluorescence (µXRF). A quantification method based in the fundamental parameters approach was evaluated. It was found that silicon concentration increases near the latewood ring zones, showing a periodical behavior, related to seasonal environmental events.

Chemical effects in K emission spectra of 38Sr compounds

The recent advances in the instrumental operating detection system provide better understanding of the several atomic parameters such as characteristic x-ray emission lines, relative intensity ratio and line-width, transition probabilities, Coster-Kronig transitions and fluorescence yields. At present, the qualitative and quantitative analysis in wavelength dispersive spectrometers are routinely performed by the fundamental parameter approach method, but none of the approach has been implemented in the routine analysis to test the possible influence of chemical effects in the different compounds. The study of chemical effects with high resolution curved crystals offers a great opportunity to enhance the analytical potential of WDXRF instruments. In the present work, high resolution Kα and Kβ emission spectra of 38Sr compounds has been measured with wavelength dispersive spectrometer. First time, spectral structures correlated to the satellite lines and their energy differences are determined. In Kα energy region, two satellite peaks (Kα3 and Kα4) are observed. The possible causes of energy shifts such as effective charge, relative intensity ratio and line-width, screening effect, shake process and electro-negativity and their roles in different 38Sr compounds are also discussed.

Coating Thickness Determination Using X-ray Fluorescence Spectroscopy: Monte Carlo Simulations as an Alternative to the Use of Standards

X-ray fluorescence is often employed in the measurement of the thickness of coatings. Despite its widespread nature, the task is not straightforward because of the complex physics involved, which results in high dependence on matrix effects. Thickness quantification is accomplished using the Fundamental Parameters approach, adjusted with empirical measurements of standards with known composition and thickness. This approach has two major drawbacks: (i) there are no standards for any possible coating and coating architecture and (ii) even relying on standards, the quantification of unknown samples requires the precise knowledge of the matrix nature (e.g., in the case of multilayer coatings the thickness and composition of each underlayer). In this work, we describe a semiquantitative approach to coating thickness measurement based on the construction of calibration curves through simulated XRF spectra built with Monte Carlo simulations. Simulations have been performed with the freeware software XMI-MSIM. We have assessed the accuracy of the methods by comparing the results with those obtained by (i) XRF thickness determination with standards and (ii) FIB-SEM cross-sectioning. Then we evaluated which parameters are critical in this kind of indirect thickness measurement.

Structure of high resolution Lα and Lβ1 x-ray emission spectra of 38Sr compounds

The recent advances in the instrumental operating detection system provide better understanding of the several atomic parameters such as characteristic x-ray emission lines, relative intensity ratio and line-width, transition probabilities, Coster-Kronig transitions and fluorescence yields. At present, the qualitative and quantitative analysis in wavelength dispersive spectrometers are routinely performed by the fundamental parameter approach method, but none of the approaches have been implemented in the routine analysis to test the possible influence of chemical effects in different chemical compounds. The study of chemical effects with high resolution curved crystals offers a great opportunity to enhance the analytical potential of WDXRF instruments. In the present work, high resolution Lα and Lβ1 emission spectra of 38Sr compounds have been measured with wavelength dispersive spectrometer. First time, spectral structures correlated to the satellite lines and their energy shifts are determined. In Lα energy region, three satellite peaks (Lα′, Lα″ and Lα‴) and in Lβ1 region, two satellite peaks (Lβ1′ and Lβ1″) are observed. To confirm the origin of the satellite peaks associated with each of the Lα and Lβ1 diagram lines, we have calculated the theoretical values of energies by using available Hartree-Fock-Slater approximation based on K-LM and L-MN Auger transition energies. The measured and calculated values of the satellite peak energies are found in good agreement with each other. The possible causes of energy shifts such as Coster-Kronig transitions, effective charge, relative intensity ratio and line-width, screening effect, shake process and electro-negativity and their roles in different 38Sr compounds are also discussed.