Interelement Effects Research Articles

Computer-guided alignment II :Optical system alignment using differential wavefront sampling

We present a differential wavefront sampling method for the efficient alignment of centred optical systems. Using the inter-element effects reported in our previous study, this method generates a linear symmetric matrix that relates the optical wavefront to misalignments within the system. The solution vector of this matrix equation provides a unique description of decentre and tilt misalignments of the system. We give a comparison of this approach to the existing method in the first case study and then illustrate characteristics of the new approach using the subsequent four case studies and Monte-Carlo alignment simulations. The results reveal superiority of the method over the existing one in misalignment estimation accuracy and demonstrate the practical feasibility and robustness.

Quantitative analysis of chromite ores using glass discs in moderate dilutions of lithium tetraborate by x‐ray fluorescence spectrometry

AbstractA method for the quantitative analysis of chromite ores by x‐ray fluorescence spectrometry using beads is proposed. The work concerned the serious problems caused by the refractory nature of these materials which prevents the use of glass discs in x‐ray fluorescence. An in‐depth study was done to optimise the variables which influence the glass disc formation process. Sufficiently homogeneous glass discs were obtained under the following experimental conditions: lithium tetraborate as flux with moderate sample dilution (1:40), with the addition of one or two drops of LiBr solution(250 g l−1), at a temperature of 1200 °C for 30 min. The qualitative and semiquantitative results for the chromite ores provided synthetic standards based on combinations of similar reference materials and different pure ignited oxides. These standards were used to obtain the calibration curves for Cr, Si, Al, Fe, Ti, Ca, Mn, Mg, Na and K oxides, with root mean square error always below 0.357. The calibration curves were used in the quantitative analysis of chromite ores with satisfactory accuracy, justifying compensation of the interelemental effects. The suggested method is an efficient solution to the problems with the quantitative analysis of this type of material by XRF. Copyright © 2006 John Wiley & Sons, Ltd.

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

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

X-ray Fluorescence Analysis of Flux-Cored Wire Burden

Interelement effects were estimated for the burden components of the PP-AN4 flux-cored wire, and the predominance of absorption effects was demonstrated. Reasons for the variation of the effective wavelengths in the primary excitation spectrum were revealed for some analytes. An iteration Δμ-correction method was proposed for calculating the weight portions of elements. This method is based on the regression analysis of the absorption parameters of test samples; it takes into account the variation of the effective wavelength of the primary radiation. The convergence of the iteration procedure was shown in the calculations of the weight portions of burden elements under real conditions. A method was proposed for the preparation of burden samples for analysis taking into account the peculiar features of the technological process. Metrological certification was performed in accordance with the industry-specific regulations. The results of X-ray fluorescence analysis of the burden were used for the quality control of the produced flux-cored wire.

Métodos matemáticos para correção de interferências espectrais e efeitos interelementos na análise quantitativa por fluorescência de raios-X

One of the main problems in quantitative analysis of complex samples by x-ray fluorescence is related to interelemental (or matrix) effects. These effects appear as a result of interactions among sample elements, affecting the x-ray emission intensity in a non-linear manner. Basically, two main effects occur; intensity absorption and enhancement. The combination of these effects can lead to serious problems. Many studies have been carried out proposing mathematical methods to correct for these effects. Basic concepts and the main correction methods are discussed here.

Determination of metals in lubricating oils by X-ray fluorescence spectrometry

The determination of common wear metals, namely iron, chromium, copper, zinc and lead, in a wide range of lubricating oil samples was investigated for the use of a low-cost, wavelength-dispersive X-ray fluorescence spectrometer. The procedure provided results in satisfactory agreement with inductively coupled plasma spectrometry used as reference method after microwave digestion of the samples in concentrated nitric acid. Statistical tests following extensive regression analyses of the data indicated that interelement effects were not statistically significant and that a simple linear regression was adequate for the calibration of individual metals.

Preconcentration and elimination of matrix effects in XRF determinations of rare earth elements by preparing a thin film through chemofiltration

Trace rare earth elements (REE) can be enriched by collecting them on a filter after they have formed their complexes with 2,2′-(1,8-dihydroxy-3,6-disulfonaphthylene-2,7-bisazo)bisbenzenearsonic acid (Arsenazo III) through a process called chemofiltration. The filter, which constitutes a thin film, is passed directly to the X-ray fluorescence (XRF) spectrometer, eliminating, in this manner, the interelemental effects produced in XRF determinations. High preconcentration factors and low detection limits are obtained: 18.3 ng mL−1 for Sm, 17.5 ng mL−1 for Eu and 34 ng mL−1 for Gd. The method was applied to the determination of these elements in NIST standard reference glasses with very good precision.

Enrichment method for trace amounts of rare earth elements using chemofiltration and XRF determination

A preconcentration method for subsequent determination of rare earth elements (REE) by X-ray fluorescence (XRF) spectrometry was developed. The method is based on using (o-[3,6-disulfo-2-hydroxy-1-naphthylazo]-benzenearsonic acid) (Thorin) as a complexing agent which is retained on a polyamide membrane by a chemofiltration process. The pH dependence of the chemofiltration of these metal ions on the membrane and other variables, such as flow-rate, contact time, kinetic of complex formation, etc. were determined. The membrane containing the chemofiltrate formed a thin film, which eliminated the interelemental effects when measured by XRF. The detection limits were 23, 23 and 49 ng/mL for Sm(III), Eu(III) and Gd(III), respectively. High enrichment factors were obtained. The method was successfully applied to the preconcentration of Sm(III), Eu(III) and Gd(III) from different samples.

Matrix effects during trace element analysis in plant samples by inductively coupled plasma atomic emission spectrometry with axial view configuration and pneumatic nebulizer

Plant sample matrix effects have been investigated during trace element analysis by inductively coupled plasma atomic emission spectrometry with axial view and pneumatic nebulizer. Eight elements often analyzed in environmental samples were studied: As, Cd, Co, Cr, Cu, Ni, Pb and Se. To simulate the effects caused by digested plant samples, the spectral line profiles of analytes were measured on solutions containing various concentrations of elements encountered in plant matrix such as K, Ca and Mg. Depressions in the emission intensities occurred and were more dramatic with high concentrations of the concomitant species. The inter-element effects were found to be caused by the matrix amount entering into the central channel of the plasma. In fact, energy consumed for droplets desolvation and particles of salts vaporization leads to lower plasma temperatures and produce changes in excitation mechanisms. Ion emissions were especially affected. The matrix effects can be removed using a high generator power (1.4 kW) and a moderate uptake flow rate of solution into the plasma (pump speed: 15 rev./min). The use of the natural plant sample led to the same conclusions. These operating conditions decreased the sensitivity but routine analyses of the plant material could be carried out.

Nonsolvent quantitation of anionic surfactants and other inorganic ingredients in laundry detergent products by X‐ray fluorescence spectrometry

AbstractThis paper reports the development of a method for measuring alkyl‐benzene sulfonates, alkyl sulfates, and other inorganic ingredients in laundry detergent products without requiring the use of chlorinated organic solvents such as chloroform. Zeolite is first filtered as a residue on filter paper from an aqueous detergent solution. A calcium solution is then added to the filtrate. Alkyl‐benzene sulfonates, alkyl sulfates, and phosphate are precipitated as calcium salts and recovered as residues via filtration. The filters are then subjected to X‐ray fluorescence spectrometry (XRF) for measuring the levels of zeolite, phosphate, and total anionic surfactant. The remaining filtrate is also subjected to XRF by using the microdroplet preparation for measuring levels of sulfate and silicate. Separately, the level of alkyl‐benzene sulfonates is measured following the same XRF procedure after alkyl sulfates are hydrolyzed using an autoclave. This sample preparation procedure was investigated using XRF and was confirmed to be applicable for simultaneous measurements of alkyl‐benzene sulfonates, alkyl sulfates, zeolite, phosphate, silicate, and sulfate without using any organic solvents. In the method described in this paper, interelement effects between anionic surfactants and phosphate are not negligible. Fluorescent X‐rays of sulfur or phosphorus are absorbed by calcium complexes of phosphate or anionic surfactants. The slope of calibration curves varies with the levels of coexistent elements; external calibration methods cannot be employed for unknown sample matrices. However, for quality assurance purposes, this method is ideal in terms of turnaround time and laboratory hygiene.

An attempt at improving the accuracy of calculated relative intensities from theory in x-ray fluorescence spectrometry

The effects of different spectrometer geometries, x-ray tube spectral distributions and mass absorption coefficients (MACs) on relative intensities calculated from the theory have been investigated. In the comparison of calculated relative intensities with experimental data for eight analyte components and nine characteristic x-ray lines in a fusion sample system, four different published mass absorption coefficient compilations were employed and three different intensity calculation modes were used. It was observed that the most significant MAC differences (up to 46% relative) appeared between these MAC compilations, or between calculated and experimental MAC values when the lines under examination were located between the energy ranges of L II and L III , or M IV and M V absorption edges of an absorber. This leads to large differences (up to 23%) between calculated relative intensities when using the four different MAC compilations. A mixed MAC compilation and a (μ+τ) calculation mode were proposed which led to better agreements between calculated and measured relative intensities on a series of synthetic standards. More accurate theoretical α-coefficients calculated from the theory and analytical results of the direct fundamental parameter method for the correction of inter-element effects would be expected when the accuracy of calculated relative intensities was improved.

Use of Laser-Ablation ICP-MS for U-Pb Zircon Geochronology

Zircon is the most frequently used mineral for age determination with the U-Pb dating technique, despite its disadvantage of highly complex growth structures, inheritance of older pre-crystallization lead and its tendency to lose some of the radiogenic lead through the further P-T-evolution. Geological processes in deep crustal rocks are known to be very complex and polyphased and in part can be of short duration. The unravelling of such complex evolutionary histories demands for both high precision dating and high spatial resolution of different growth stages that have been visualized by imaging methods such as cathodoluminescence or backscatter electron imaging proir to isotopic dating. Isotope dilution thermal mass-spectrometry (IDTIMS) allows the assessment of highly precise U-Pb ages within a few permil uncertainty. Complex growth structures and/or system behaviour are, however, only resolved by in-situ analyses, e.g. using an ionprobe. Laserablation ICP-mass spectrometry now offers a third possibility for accurate, fast and cheap determination of U-Pb ages. The introduction of UV lasers lead to improved ablation behaviour (Gtinther et al., 1997), reduced inter-elemental fractionation effects and improved accuracy when compared to Nd:YAG lasers (e.g. Hirata and Nesbitt, 1995).

A new approach to quantitative x‐ray microfluorescence analysis of individual particles

In the x-ray microfluorescence analysis of particles, the characteristic line intensity depends not only on the chemical composition of the sample, but also on the x-ray beam profile, particle size, shape and orientation. In previous work, optical measurements of particle dimensions were required to develop parametric equations for correction of both particle size and interelement effects. In that work the measurement of particle dimensions was limited in accuracy by the optical system used. A different approach here is described in which an estimate of the size of an irregularly shaped particle is obtained indirectly. This technique is particularly useful for the analysis of particles in which the concentrations of low atomic number elements are known or can be obtained from stoichiometry. This procedure has been tested with irregularly shaped, homogeneous glass particles of known composition and size ranging from 50–150 μm using an x-ray microbeam 177 μm in diameter. © 1997 John Wiley & Sons, Ltd.

A new approach to quantitative x-ray microfluorescence analysis of individual particles

In the x-ray microfluorescence analysis of particles, the characteristic line intensity depends not only on the chemical composition of the sample, but also on the x-ray beam profile, particle size, shape and orientation. In previous work, optical measurements of particle dimensions were required to develop parametric equations for correction of both particle size and interelement effects. In that work the measurement of particle dimensions was limited in accuracy by the optical system used. A different approach here is described in which an estimate of the size of an irregularly shaped particle is obtained indirectly. This technique is particularly useful for the analysis of particles in which the concentrations of low atomic number elements are known or can be obtained from stoichiometry. This procedure has been tested with irregularly shaped, homogeneous glass particles of known composition and size ranging from 50–150 μm using an x-ray microbeam 177 μm in diameter. © 1997 John Wiley & Sons, Ltd.

New findings in the spectrometric determination of steel nitrogen levels

The efficiency of analyzing nitrogen by optical emission spectroscopy was put to test in a first publication by six German laboratories of the iron and steel industry. Further experiences with this new method accumulated in the meantime will be reported here. By taking into account interelement effects both the residual scatter and BEC (background equivalent concentration) values for alloy steels have clearly been improved. The detection limit was determined at 6 μg/g by using the repeatability standard deviation in the range of the spectral background. Precipitates of titanium nitrides or carbon nitrides lead to high scatter of measured values. The long-term stability of the spectrometric measuring system is largely dependent on the purity of the argon gas, transmission conditions in the spectral apparatus, the properties of the excitation unit, and the quality of the specimen surface. To all these items recommendations for practice are given.

Determination of Calcium in Certain Fertilizers by Inductively Coupled Plasma Atomic Emission Spectrometry: Studies of Some Spectral and Interelement Effects at Different Wavelengths

Abstract Four analytical wavelengths (393.366, 396.847, 317.933, and 422.673 nm) were used to determine Ca in 2 fertilizers by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Matrix effects were studied by adding to real fertilizer solutions fertilizer elements that are known or believed to interfere with Ca determination. Matrix effects were calculated by multiple linear regression. Interference was caused by S, K, or B. At 422.673 nm, the interference of B and K is a spectral effect, and at 396.847 and 317.933 nm, the interference of S and K is an interelement effect. At 393.366 nm, no linear interference was found. The best wavelength for determining Ca in fertilizers by ICP-AES is 396.847 nm.

Determination of Sulfur in Fertilizers by Inductively Coupled Plasma-Atomic Emission Spectrometry: Spectral and Interelement Effects at Various Wavelengths

Abstract Three analytical wavelengths (180.731,182.037, and 182.625 nm) were tested for determination of sulfur in 2 fertilizers by inductively coupled plasmaatomic emission spectrometry (ICP-AES). Variable S results at 182.037 nm were caused by a downward sloping background shift (Fe line at 181.851 nm) during measurement of the sample solutions. At 182.625 nm an emission peak doublet, 182.619/182.635 nm, was observed from which the instrument selected the measurement peak. A shift from calibrated peak 182.619 nm to noncalibrated peak 182.635 nm occurred when the S/B ratios were ≤22-31 in the fertilizer samples examined. For the 3 wavelengths of S investigated, the pattern of spectral and interelement interference changed at the same wavelength according to the composition of the fertilizer. K, P, and Mg typically caused interelement effects and Ca and B caused spectral effects during S determination. In the interference studies, 180.731 nm proved the best wavelength for the ICP-AES determination of S in fertilizers. Interlaboratory studies showed the accuracy of the method to be ± 6.2% for both water- and acid-soluble S, independent of the measurement wavelength, instrument, and operator.

Determination of antimony, arsenic, bismuth and copper by inductively coupled plasma atomic emission spectrometry in the electrorefining of copper.

Inductively coupled plasma atomic emissionspectrometry (ICP-AES) has been applied as a rapid and routine method for the analysis of process electrolytes in the electrorefining of copper. Antimony, arsenic, bismuth and copper have been selected as major electrolyte constituents. For these elements profound statistical studies of spectral and interelement effects have been carried out. For As, Bi and Sb two analyte wavelengths have been selected, and for Cu one relatively insensitive analyte line has been chosen due to the high Cu concentration in samples. Best analytical lines were: As at 193.759 nm, Bi at 306.772 nm, Sb at 206.833 nm and Cu at 216.953 nm. Multiple linear regression proved to be very capable in the search of the best analytical wavelength and identifying interfering elements. Using simple acid based standards all elements investigated can be determined separately in complicated matrices with satisfactory results. Differences between true values and measured values can be partly eliminated by appropriate calculational methods.

Stability of bacterium-mercury complexes and speciation of soluble inorganic mercury species

Soluble inorganic mercury ions from aqueous solutions were retained on the external membrane of both lyophilized bacterial cells and living cells. Desorption studies were performed using both types of cells. Distribution coefficients of mercury between the aqueous and solid phases, as well as the conditional stability constants of mercury ions for the external membranes of bacteria were calculated. Loaded membranes and the amount of the unadsorbed ions were measured by electrothermal atomic absorption spectrometry (ETAAS) and/or gamma spectrometry. The 203Hg radiotracer ( t 1 2 = 46.6 days ) was used to monitor recoveries using gamma spectrometry in combination with an optimized extraction procedure. Depending on the pH of the solution mercury ions can be selectively retained by the bacterial external membrane and the speciation of the mercury(II) and mercury(I) ions is possible. Best retention pHs for both mercury ions and bacteria were the following: mercury(II): 1 ( E. coli) and 3 ( P. putida), and mercury(I): 4 ( E. coli) and 8 ( P. putida). Interelement effects from other ions in the retention process of mercury were also investigated. A technique involving a solid extraction stage of mercury from aqueous samples at ng ml −1 level was developed and applied to the determination of mercury by ETAAS. The mercury-biomass pellet is separated by centrifugation and treated with a nitric acid solution determining the content of mercury in the supernatant solution. The best detection limit (3 times stand. dev. of the blank) and the best sensitivity (Hg concentration for an absorbance peak of 0.0044s) of the method for the applied concentration procedure were, respectively, of 15.0 ng ml −1 and 3.0 ng ml −1 for mercury(I) and 22.0 ng ml −1 and 5.5 ng ml −1 for mercury(II).

Hyperbolic model of the addition-dilution method in quantitative X-ray fluorescence analysis

A mathematical model based on a combination of the total addition method (TAM) and limit dilution method (LDM) is proposed. The model shows the hyperbolic behaviour of the experimental data when the X-ray fluorescence intensities are represented versus the addition-dilution factor [ (1 − ƒ n) ƒ n ]. The equation obtained for the chemical system can be split into two terms, which relate directly to the processes of addition of the standard and dilution of the unknown. This equation fits mathematically to a hyperbolic function from which physical parameters and data of analytical interest are obtained for the samples studied. In the proposed model, some parameters are defined which are equivalent to the fluorescence intensity of the analyte in the normalised sample ( I i s), in the standard ( I i p) and the corrected intensity ( I i sc) respectively. These parameters allow determination of the analyte concentration in an unknown and a suitable algorithm is proposed for their calculation. The proposed model is applied to the determination of Zn, Ti and Zr in a synthetic sample, prepared by homogenising the respective metal oxides. The results are in complete agreement with the contents which suggests a good correction of the strong interelement effects typical at these levels of concentration as is demonstrated by a low error in an interval of 0.7–1.2%.