Quantitative X-ray Fluorescence Analysis Research Articles

The Copper CHARM Set: A New Set of Certified Reference Materials for the Standardization of Quantitative X-Ray Fluorescence Analysis of Heritage Copper Alloys*

This paper introduces a new set of certified reference materials designed to aid scientists and conservators working in cultural heritage fields with quantitative X-ray fluorescence analysis of historical and prehistoric copper alloys. This set has been designated as the Copper CHARM Set (Cultural Heritage Alloy Reference Material Set). The Copper CHARM Set is designed to be used by a wide range of museum-, art- and archaeology-oriented scientists and conservators to help improve the accuracy and range of their calibrations for quantitative ED–XRF spectrometry of copper alloys, and also increase the number of elements that can routinely be quantified. In addition, the common use of a single core set of the reference materials is designed to significantly improve inter-laboratory reproducibility, allowing greater data sharing between researchers and thus furthering possibilities for collaborative study.

A new Monte Carlo code for simulation of the effect of irregular surfaces on X-ray spectra

Generally, quantitative X-ray fluorescence (XRF) analysis estimates the content of chemical elements in a sample based on the areas of the fluorescence peaks in the energy spectrum. Besides the concentration of the elements, the peak areas depend also on the geometrical conditions. In fact, the estimate of the peak areas is simple if the sample surface is smooth and if the spectrum shows a good statistic (large-area peaks). For this reason often the sample is prepared as a pellet. However, this approach is not always feasible, for instance when cultural heritage or valuable samples must be analyzed. In this case, the sample surface cannot be smoothed. In order to address this problem, several works have been reported in the literature, based on experimental measurements on a few sets of specific samples or on Monte Carlo simulations. The results obtained with the first approach are limited by the specific class of samples analyzed, while the second approach cannot be applied to arbitrarily irregular surfaces. The present work describes a more general analysis tool based on a new fast Monte Carlo algorithm, which is virtually able to simulate any kind of surface. At the best of our knowledge, it is the first Monte Carlo code with this option. A study of the influence of surface irregularities on the measured spectrum is performed and some results reported.

Quantitative X-ray fluorescence analysis of multielemental subjects of complex shape without implementation of reference standards

A theoretical dependence of the ratio of intensities of X-ray fluorescence lines of chemical elements on the ratio of their concentration in a sample is suggested. The effect of various experimental factors on parameters of the obtained model is considered. A method of quantitative X-ray fluorescence analysis of multielemental subjects using the suggested calibration dependence without the implementation of reference standards is described. The adequacy and analytical advantages of the developed approach are demonstrated for the determination of the elemental composition of a sample of a metal alloy of complex shape.

Quantitative X-ray Fluorescence Analysis of Biomass: Objective Evaluation of a Typical Commercial Multi-Element Method on a WD-XRF Spectrometer

With the increasing utilization and trade of biomass, there is a growing need for quick and reliable quantitative chemical analysis of the inorganic elemental composition of biomass. X-ray fluoresc...

Analytical capabilities of a monochromatic model of X-ray fluorescence excitation by inhomogeneous radiation for multi-element subjects

New aspects of a monochromatic model of X-ray fluorescence excitation by bremsstrahlung and mixed X-ray tube radiation were examined in this paper. Analytic algorithms for calculation of the parameters of a virtual monochromatic source for complicated multicomponent subjects with different compositions and thicknesses were developed. Algorithm adequacy was tested during quantitative X-ray fluorescence analysis of metal alloys, slag, and ore concentrates.

Size-resolved source apportionment of aerosol particles using polycapillary X-ray lens with a plateau in its focal spot

A laboratory micro X-ray fluorescence spectrometer based on a special polycapillary X-ray lens (PXRL) was used to carry out the source apportionment of aerosol particles. In the curve of the distribution of the X-ray intensity in the focal spot of the special PXRL, there was a plateau with a diameter of 21.3 μm in which the distribution of the X-ray intensity was homogeneous. The gain in flux density in the plateau of the PXRL is 1490. The uniformity of this plateau was 2.9%. This was helpful for the quantitative X-ray fluorescence analysis of a single aerosol particle with smaller size than that of the plateau of the PXRL. The fingerprint database of aerosol particles with given sizes from various air pollution sources was established with the single particle analysis method. The size-resolved source apportionment of aerosol particles in haze in Beijing city was performed with this fingerprint database.

XRF analysis without sampling of Etruscan depurata pottery for provenance classification

In order to settle the provenance of a set of ancient ceramic shards, the elemental composition data acquired are usually treated by multivariate analysis techniques. The quantitative X-ray fluorescence (XRF) analysis is an appropriate tool if it is possible to grind ceramics and analyze a sample that is representative of the object. If we deal particularly with well-preserved objects, we are often not allowed to sample them. Moreover, moving these objects from museum could be unfeasible as well. The aim of this work is to evaluate if spot XRF analysis on integral objects is adequate to classify row clay provenance even if ceramics is not an intrinsically homogeneous material. So, we performed measurements on a set of Etruscan fine ware already classified according to the archaeological, chemical and mineralogical examination. For each sample, several measurement points in polished areas were considered for XRF analyses, allowing a correct provenance classification. Copyright © 2010 John Wiley & Sons, Ltd.

Optimization of the quantitative direct solid total-reflection X-ray fluorescence analysis of glass microspheres functionalized with Zr organometallic compounds

Quantitative determination of Zr in the system constituted by quartz microspheres functionalized with two kinds of organometallic compounds has been studied due to the importance of the correct quantization of the Zr from a catalytic point of view. Two parallel approximations were done, i.e. acid leaching and direct solid quantization. To validate the acid leaching TXRF measures, ICP-MS analysis were carried out. The results obtained by means of the optimization of the quantitative direct solid procedure show that, with a previous particle size distribution modification, TXRF obtain the same analytical results as ICP-MS and TXRF by acid leaching way but without previous chemical acid manipulation. This fact implies an important improvement for the analysis time, reagents costs and analysis facility and it proves again the versatility of TXRF to solve analytical problems in an easy, quick and accurate way. Additionally and for the direct solid TXRF measurements, a deeper study was done to evaluate the intrinsic analytical parameters of the Zr TXRF analysis of this material. So, the influence of the particle size distributions (modified by means of a high power ultrasound probe) with respect to uncertainty and detection limits for Zr were developed. The main analytical conclusion was the strong correlation between the average particle sizes and the TXRF analytical parameters of Zr measurements, i.e. concentration, accuracy, uncertainty and detection limits.

Quantitative X-ray fluorescence analysis of As-Se glasses and films

The concentrations of arsenic and selenium in As100 − x Se x glassy alloys and related films have been determined by the X-ray fluorescence spectroscopy using the external standard technique. It is demonstrated that the proposed approach allows the compositions of As100 − x Se x glasses and films to be quantitatively determined with an accuracy of Δx = ±0.02.

Quantitative analysis of single aerosol particles using polycapillary X-ray optics

A laboratory micro X-ray fluorescence spectrometer based on polycapillary X-ray optics (PXRO) was used to carry out the quantitative X-ray fluorescence analysis of single aerosol particles with smaller size than that of focal spot of PXRO. The minimum detection limits measured with the thin-film reference standards were in the range from 13.3 to 0.7 ng cm − 2 when the operating current and voltage were 70 mA and 35 kV, respectively. In order to reduce the effects of the inhomogeneous distributions of the X-ray intensity in the focal spot of the PXRO on the analysis results, the sensitivities were corrected by using a Gaussian function for the quantitative analysis of single aerosol particles. The accuracy of the analysis of single standard solution drops was on average 25% depending on the element and concentration. The precision of the analysis was better than 5%.

Multilayers quantitative X-ray fluorescence analysis applied to easel paintings

X-ray fluorescence spectrometry (XRF) allows a rapid and simple determination of the elemental composition of a material. As a non-destructive tool, it has been extensively used for analysis in art and archaeology since the early 1970s. Whereas it is commonly used for qualitative analysis, recent efforts have been made to develop quantitative treatment even with portable systems. However, the interpretation of the results obtained with this technique can turn out to be problematic in the case of layered structures such as easel paintings. The use of differential X-ray attenuation enables modelling of the various layers: indeed, the absorption of X-rays through different layers will result in modification of intensity ratio between the different characteristic lines. This work focuses on the possibility to use XRF with the fundamental parameters method to reconstruct the composition and thickness of the layers. This method was tested on several multilayers standards and gives a maximum error of 15% for thicknesses and errors of 10% for concentrations. On a painting test sample that was rather inhomogeneous, the XRF analysis provides an average value. This method was applied in situ to estimate the thickness of the layers a painting from Marco d'Oggiono, pupil of Leonardo da Vinci.

Quantitative X-ray fluorescence analysis of an Egyptian faience pendant and comparison with PIXE

The X-ray fluorescence (XRF) technique is a common choice in the archaeometric field for in situ investigations with portable instruments. This work shows that XRF portable systems can be used for quantitative analyses using appropriate software, obtaining a similar accuracy to that provided with other techniques such as particle-induced X-ray emission (PIXE), as shown for an Egyptian faience pendant and for two glass standards.

F-57 Invited—Considerations on Calibration and Prediction in Quantitative X-ray Fluorescence Analysis

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Monochromatic model of X-ray fluorescence excitation by polychromatic radiation: New algorithms and analytical applications

An alternative approach was proposed to calculate the parameters of a virtual monochromatic source in the excitation of X-ray fluorescence of multicomponent samples with polychromatic radiation. Analytic expressions were obtained for the calculation of the equivalent wavelength of bremsstrahlung and mixed excitation spectrum for samples of arbitrary composition and thickness. The efficiency of the developed approach in quantitative X-ray fluorescence analysis with consideration for matrix effects was demonstrated.

The effects of absorption edge structure of atoms in x‐ray fluorescence analysis

AbstractThe effects of the absorption edge structure in x‐ray fluorescence (XRF) manifest themselves as a very strong attenuation of the analytical line radiation when it is in the x‐ray absorption near edge structure (XANES) range. In this paper, this effect is exemplified by an ultra‐strong Ba‐caused attenuation of the Ce Lβ1 line. This case was experimentally studied. Comparison of measured and calculated relative intensities has shown that the actual mass attenuation coefficient of the Ce Lβ1 line in Ba is 1.6 times greater than known values. This is due to that the Ce Lβ1 line is within the initial range of L3 Ba absorption edge, i. e. the XANES range. Such an effect of the absorption edge structure of atoms must be considered using the fundamental parameters method in quantitative XRF analysis. This paper also presents some other possible cases of this effect. Copyright © 2009 John Wiley & Sons, Ltd.

Excitation of X-ray fluorescence of massive samples by bremsstrahlung: Analytical possibilities of the monochromatic model

An algorithm was proposed for calculation of the equivalent analytical wavelength of the bremsstrahlung spectrum during X-ray fluorescence excitation in multicomponent objects of arbitrary thickness. A correlation is found between the analytically obtained approximate values of a given parameter and its exact values found numerically taking into account the design features of an X-ray tube. The approach makes it possible to minimize the error of the results of quantitative X-ray fluorescence analysis of samples of various thicknesses taking into account the matrix effects.

Excitation of X-ray fluorescence of thin-film samples by bremsstrahlung: Extension and analytical possibilities of the monochromatic model

Different approaches to the description of X-ray fluorescence excitation in thin films by bremsstrahlung within the monochromatic model are systematically expounded and compared. New analytical expressions are proposed for calculation of the wavelength of a virtual monochromatic excitation source. It is shown that some of them can be successfully used in quantitative X-ray fluorescence analysis of semiinfinite samples, including matrix effects, without a priori information on an analyte.

About the dependence of the intensity of X-ray spectra of elements on their concentrations expressed in atomic and mass percents

The consideration of the classical physical fundamentals of X-ray spectrometry suggests that the properties of X-ray spectra of elements are determined by their atomic number rather than atomic weight. The intensity of X-ray spectra is determined by the number of excited atoms rather by their mass. However, in the middle of the 20th century, the dependence of intensity on the mass concentration of elements was introduced without any physical grounds. The paper presents physical, analytical, and metrological evidences for the idea that this dependence does not correspond to a real physical process. It results in distorted calibration characteristics and extra errors and hinders the development of a method of universal (for all element systems) quantitative X-ray fluorescence analysis instead of specific procedures with empirical parameters for each particular system. The dependence on atomic concentrations eliminates these difficulties.

Effect of the sample matrix on measurement uncertainty in X-ray fluorescence analysis

The estimation of measurement uncertainty, with reference to univariate calibration functions, is discussed in detail in the Eurachem Guide “Quantifying Uncertainty in Analytical Measurement”. The adoption of these recommendations to quantitative X-ray fluorescence analysis (XRF) involves basic problems which are above all due to the strong influence of the sample matrix on the analytical response. In XRF-analysis, the proposed recommendations are consequently applicable only to the matrix corrected response. The application is also restricted with regard to both the matrices and analyte concentrations. In this context the present studies are aimed at the problems to predict measurement uncertainty also with reference to more variable sample compositions. The corresponding investigations are focused on the use of the intensity of the Compton scattered tube line as an internal standard to assess the effect of the individual sample matrix on the analytical response relatively to a reference matrix. Based on this concept the estimation of the measurement uncertainty of an analyte presented in an unknown specimen can be predicted in consideration of the data obtained under defined matrix conditions.

The influence of scattering processes in quantitative X-ray fluorescence analysis

Existing theory was used to develop a fundamental parameter (FP) computer program for quantitative X-ray fluorescence (XRF) spectrometry in which scattering interactions are taken into account. The program is suited for polychromatic radiation and composite samples and is used to estimate the errors that result from neglecting the scattering contributions in the analysis of samples in a low Z matrix when the spectrometer is calibrated either on pure elements or on standards similar to the samples.