Measurement of peak areas in energy-dispersive x-ray fluorescence spectrometry

An algorithm is outlined for the measurement of peak areas in spectra obtained by energy-dispersive x-ray fluorescence techniques. Each fluorescence line is assumed to be a pure Gaussian function. Initially, a calibration equation relating the full width at half maximum (FWHM) to the centre of the peak is set up. Then, in an unknown spectrum, the Gauss function parameters are found by a stepwise procedure making a non-linear minimization procedure redundant. First, the background is estimated and subtracted; then the peak centres are found, and the FWHM is given by the calibration equation, which relates FWHM to the position of the peak centre. Finally, the amplitudes are estimated from a set of linear equations. The reliability of the proposed algorithm was proved for a variety of samples. The method was compared with a non-linear x² minimization routine. Quantitative analysis of two standard reference alloys was accurate. Below 20 keV, a suitable FWHM calibration is obtained from a set of K_α lines. Above 20 keV, a set of K_β1,3 lines is recommended.     

The use of the ratios of intensities of spectral lines for X-ray fluorescence analysis of metal alloys and oxide materials

An X-ray fluorescence analysis technique is proposed, which is based on using ratios of intensities of spectral lines. The technique includes performing calculations for evaluation of calibration equations, which allows using few reference samples or carrying out standardless analysis, if necessary. That parameters of the calibration equations depend linearly on concentrations of disturbing elements allows one to simplify taking their influence into account. To apply the developed technique to analysis of samples containing a significant amount of undetectable light elements, a use of a dependence of intensity ratio of the characteristic radiation of the X-ray tube’s anode, coherently and incoherently scattered by a sample, on a total content of undetectable elements is proposed. The technique’s adequacy is demonstrated by analysis of standard steel samples, metal cuttings and iron-ore materials.     

Multivariate data analysis for x-ray fluorescence spectrometry

A multivariate data analysis procedure that uses singular value decomposition and the Ho-Kashyap algorithm is proposed to obtain calibration constants for x-ray fluorescence spectrometry. These calibration constants can be used to obtain results from experimental data by means of a simple dot product calculation. The method was tested on experimental data from the literature. Comparison of results showed that the method performs at least as well or better than the Rasberry-Heinrich method or its modifications. The method can be used to express calibration results obtained with a theoretically based program in such a way that they can be used conveniently in routine applications.     

Analysis of cast iron by x-ray fluorescence spectrometry

It is shown that a wide range of cast irons can be analysed on one calibration if the sample surfaces are prepared to a mirror finish with diamond paste. Polishing the samples with any abrasive material results in preferential removal of the softer constituents from the sample matrix. If coarser abrasives than diamond paste are used, the increased depth of the introduced sample inhomogeneity leads to unacceptable error limits for the determination of light elements.     

K x-ray emission spectra from natural silicates

Chemical shifts of Si Kα_1,2 and Al Kα_1,2 lines in seven natural silicates has been measured comparatively to the lines of the pure elements. An attempt is made to correlate these shifts to the surroundings of Si and Al in the minerals.     

Development of the Method of Calibration Equations for the X-Ray Fluorescence Analysis of Multicomponent Samples in the Presence of Undetectable Elements

New calibration equations are proposed based on the use of intensity ratios of spectral lines and peaks of coherently and incoherently scattered characteristic radiation of an X-ray tube. Prospects for their application to the X-ray fluorescence analysis of samples containing undetectable light elements are shown. The proposed method ensures high precision of determination and performance of analysis in the lack of adequate reference samples. The method was tested on an example of analysis of standard samples of bronze and samples of iron oxide materials.     

Qualitative and semi-quantitative analysis in ICP-AES using multivariate calibration

This paper describes a two step algorithm for qualitative and semiquantitative analysis in inductively coupled plasma—atomic emission spectroscopy (ICP-AES) including the preceding data acquisition. Sample and calibration spectra were recorded in 0.05 nm spectral windows centered about the most prominent lines of the 49 covered elements. In the first step of the analysis of an unknown sample spectrum it is decided which of these elements can be excluded from further operations because of the absence of their most prominent lines applying a multivariate criterion for peak detection. For the remaining elements quantitative analysis is performed via multivariate calibration taking into consideration the most prominent line of each element and possibly interfering lines of those elements which were not found absent during the first step. After the estimation of the element concentrations multivariate detection limits are used as criterion for the presence of an element. Results for six synthetic samples of increasing complexity prepared from standard solutions and three standard reference materials are given.     

Statistical and probabilistic approaches to confidence intervals of linear calibration in liquid chromatography.

The aim of this paper is to compare the reliability of two approaches to estimate the 95% confidence intervals of linear calibration in real situations. One is the statistical approach, which is well known in statistics, and the other is the probabilistic approach, which is based on a theory to predict the precision of instrumental analyses mainly from signal and noise, called FUMI (Function of Mutual Information) theory. The high-performance liquid chromatographic determination of quisalofop and maltose is taken as an example. Calibration lines obtained under the same experimental conditions are superimposed on the 95% confidence intervals to investigate whether the resulting confidence intervals can include all the calibration lines reasonably. A pair of 95% confidence intervals (upper and lower limits) can be calculated from each calibration line, but varies from calibration line to calibration line, although obtained under the same experimental conditions. The variability and reliability of the 95% intervals are also examined.     

A comparative study of laser induced breakdown spectroscopy analysis for element concentrations in aluminum alloy using artificial neural networks and calibration methods

A comparative study of analysis methods (traditional calibration method and artificial neural networks (ANN) prediction method) for laser induced breakdown spectroscopy (LIBS) data of different Al alloy samples was performed. In the calibration method, the intensity of the analyte lines obtained from different samples are plotted against their concentration to form calibration curves for different elements from which the concentrations of unknown elements were deduced by comparing its LIBS signal with the calibration curves. Using ANN, an artificial neural network model is trained with a set of input data of known composition samples. The trained neural network is then used to predict the elemental concentration from the test spectra. The present results reveal that artificial neural networks are capable of predicting values better than traditional method in most cases.     

An expression of uncertainty in calibration using stepwise or separate dilution of a stock solution.

The traditional method for linear calibration can estimate the confidence intervals of calibration lines from a set of experimental data for a single calibration line. However, the following situations, often encountered in laboratories, are out of reach of the method, since the concentrations of the standard solutions are not independent of each other: (A) a standard solution is diluted from a more concentrated one in a stepwise way (stepwise dilution); (B) every standard solution for a calibration experiment is prepared from a stock solution, but the stock solution is newly prepared for each calibration (separate dilution with the variable concentration of the stock solution). This paper puts forward a theory to calculate the confidence intervals of calibration lines in the above situations. Analyses made up of sample weighing, dilution, HPLC measurement and calibration with the linear least-squares fitting are taken as examples. The proposed theory is numerically compared to the traditional method.     

Particle-induced x-ray emission spectrometry: an accurate technique in the analysis of biological environmental and geological samples

The various stages of procedures based on particle-induced x-ray emission spectrometry are discussed. These include standardization (calibration of the equipment), sample and target preparation, contamination (blank) control, target bombardment, spectral data processing, and correction for matrix effects. Aspects requiring particular attention are indicated and optimization of these stages is outlined. Examples are given to demonstrate that optimized procedures can provide precise and accurate concentration data for trace elements in biological, environmental and geological samples.     

Practical implementation of survey analysis in inductively coupled plasma optical emission spectrometry

The combination of an echelle/charge coupled device detector based spectrometer with software for multicomponent analysis (MCA) allows practical implementation of survey analysis in inductively coupled plasma-optical emission spectrometry (ICP-OES). MCA requires models for the pure components. A procedure is described for how to obtain the models for 67 pure elements detectable in ICP-OES. In fact, each element is represented by two model vectors. Measurements at low analyte concentration provide the sensitivities for the prominent lines used in trace analysis, whereas weak lines and continuum emission are modelled with high concentration measurements. This modelling allows proper calibration for trace and major levels, and strongly reduces noise contributions. The model library is prepared once and a monitor solution, containing seven specific elements, is used to achieve a daily link with this once-only calibration (wavelength axis and sensitivity). To control the efficiency of atomization and ionization the Cr ii 267 nm to Cr i 357 nm ratio is used. The MCA calculations are repeated at different intensity levels in order to cover the dynamic range in intensity and, hence, concentration for all the elements present in the sample solution. Matrix-matching of the monitor solution was studied in order to overcome matrix effects owing to high acid or salt contents. Some certified reference materials were analysed. The results for most elements are found within 20% of the certified values.     

Adjustment of numerical models for gamma-ray spectra of samples when subtracting spectra of matrix elements in neutron activation analysis

Approaches to adjustment of numerical models for gamma-ray spectra of matrix elements are considered. These approaches are aimed at (1) the elimination of the substrate effect in the preparation of the initial spectra of individual elements, (2) the energy calibration of spectra, (3) the improvement of agreement between model and actually observed spectra using the comparison test for peak amplitudes of matrix elements, and (4) special processing of the spectra obtained after the subtraction of matrix elements in the test samples. The adjustment allows the contribution of matrix elements to be more precisely subtracted from the spectra of the samples under study. Thus, additional analytical lines are obtained for some elements, and detection limits are lowered for the majority of lines produced by the standard method of spectrum processing. This extends the potential of neutron activation analysis in solving scientific and practical problems.     

Thin film characterization by total reflection x-ray fluorescence

Sensitive and accurate characterization of films thinner than a few nm used in nanoelectronics represents a challenge for many conventional production metrology tools. With capabilities in the 10¹⁰ at/cm², methods usually dedicated to contamination analysis appear promising, especially Total-reflection X-Ray Fluorescence (TXRF). This study shows that under usual configuration for contamination analysis, with incident angle smaller than the critical angle of the substrate, TXRF signal saturation occurs very rapidly for dense films (below 0.5 nm for HfO₂ films on Si wafers using a 9.67 keV excitation at 0.5°). Increasing the incident angle, the range of linear results can be extended, but on the other hand, the TXRF sensitivity is degraded because of a strong increase of the measurement dead time. On HfO₂ films grown on Si wafers, an incident angle of 0.32° corresponding to a dead time of 95% was used to achieve linear analysis up to 2 nm. Composition analysis by TXRF, and especially the detection of minor elements into thin films, requires the use of a specific incident angle to optimize sensitivity. Although quantitative analyses might require specific calibration, this work shows on Co–based films that the ratio between minor elements (W, P, Mo) and Co taking into account their relative sensitivity factors is a good direct reading of the composition.     

Variable alignment of high resolution data by cluster analysis

High resolution time-of-flight secondary ion mass spectrometry (HR TOF-SIMS) is a powerful surface analytical method. For complex samples, this technique may yield intricate spectra that are difficult to interpret visually. Chemometric methods are useful for data analysis. However, these methods require that spectra are represented in a matrix format. Variances in mass measurements caused by calibration or instrumental effects may present difficulties in properly aligning mass spectral peaks into the correct columns of the data matrix. Cluster analysis of resolution elements is proposed as an alternative approach to construct the data matrix. An automated method for optimizing the data alignment is presented and evaluated for standard steel samples.     

Direct determination of boron and zirconium in ceramic materials by flame atomic absorption spectrometry after alkali sintering and fusion

Both boron and zirconium are present in ceramic materials as major silica components and have to be determined for quality control in the ceramic industry. For boron determination, sintering with a mixture of Na2CO3 and ZnO is proposed for decomposition of samples. For zirconium determination, acid digestion using an HF-HClO4 mixture and subsequent fusion with NaKCO3 and H3BO3 is proposed as decomposition step. The AAS absorbance signal of these elements is suppressed by the fusion elements in the samples. Therefore, the calibration solutions for both B and Zr must contain an appropriate concentration of sodium, sodium-potassium, and boron salts. An AIF3 solution was used for signal enhancement and improving the linearity of the Zr calibration curve. The methods proposed are well suited for the determination of higher concentrations of both boron and zirconium in silicate samples.     

Use of tandem calibration for analyzing steels and alloys by inductively coupled plasma atomic emission spectrometry

A method is proposed for plotting calibration graphs by reference analyte solutions (tandem calibration) for the analysis of steels and alloys by inductively coupled plasma atomic emission spectrometry (ICP-AES) with spark ablation. The use of spectral lines of analytes and an internal standard with similar values of sums of ionization and excitation energy ensures an excellent repeatability and accuracy of the results of analysis using tandem calibration. A nebulizer chamber for the simultaneous introduction of solutions and solid sample aerosols into inductively coupled plasma (ICP) is designed. The optimal parameters of the introduction of sample aerosols and a method of plasma observation are chosen; the requirements for the choice of the analytical lines of analytes are proposed.     

Carbon-related matrix effects in inductively coupled plasma atomic emission spectrometry

In Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), it has been observed that the emission intensity of some atomic lines is enhanced or depressed by the presence of carbon in the matrix. The goal of this work was to investigate the origin and magnitude of the carbon-related matrix effects in ICP-AES. To this end, the influence of the carbon concentration and source (i.e. glycerol, citric acid and potassium hydrogen phthalate), the experimental conditions and sample introduction system on the aerosol characteristics and transport, plasma excitation conditions and the emission intensity of several atomic and ionic lines of a total of 15 elements has been studied. Results indicate that carbon related matrix effects do not depend on the carbon source and they become more severe when the amount of carbon loaded into the plasma increases, i.e., when using: (i) carbon concentrations higher than 5 g L^− 1; (ii) high sample uptake rates; and (iii) efficient sample introduction systems. Thus, when introducing carbon into the plasma, the emission intensity of atomic lines with excitation energies below 6 eV is depressed (up to 15%) whereas the emission intensity of atomic lines of higher excitation energies (i.e. As and Se) are enhanced (up to 30%). The emission intensity of the ionic lines is not affected by the presence of carbon. The origin of the carbon-related interferences on the emission intensity of atomic lines is related to changes in the line excitation mechanism since the carbon containing solutions show the same aerosol characteristics and transport efficiencies as the corresponding aqueous solutions. Based on the previous findings, a calibration approach for the accurate determination of Se in a Se-enriched yeast certified material (SELM-1) has been proposed.     

波长色散X射线荧光光谱法快速测定纺织面料中的铬、镍、铜

建立波长色散X射线荧光光谱快速检测纺织面料中铬、镍、铜的方法。利用树脂将标准贴衬织物复合到玻璃熔片上,在制备好的织物样片上滴加铬、镍、铜标准溶液,采用波长色散X射线荧光光谱仪检测。根据元素滴加量的变化建立校准曲线,铬、镍、铜3种元素的含量分别在0~853,0~853,0~1 706μg/g范围内与荧光强度呈良好的线性关系,相关系数r2大于0.99。方法回收率为95.0%~98.8%,测定结果的相对标准偏差为3.2%~4.8%(n=6)。利用该方法检测纺织面料中重金属元素含量,方法简便,结果准确,检测成本低。     

Automated inductively-coupled plasma optical emission spectrometry based on a sequential reading monochromator

An automated computer-controlled sequential reading monochromator system for optical emission spectrometry with an inductively-coupled plasma as source is described. The system selects the set of emission lines which are best suited for each type of sample. Multi-element analysis of major and trace elements is done automatically, including sample changing, calibration, background correction and presentation of results.