Soil analysis by thin-film energy-dispersive x-ray fluorescence

Energy-dispersive x-ray fluorescence is advantageous for trace analysis of soils present as thin films. A target thickness of about 2 mg cm^-2 provides a compromise between optimal sensitivity and minimal absorption effect or optimal accuracy. Sample preparation involves only suspending the finely ground soil in water and drying this suspension on a thin mylar foil glued on a ring that fits into the x.r.f. spectrometer. The “effective sample weight” present in the exciting beam area is computed from the scatter peaks, a method that cancels out target heterogeneity problems. High accuracy is demonstrated for many elements in reference soil and rock materials; a precision around 5% and a detection limit around 10 ppm can be achieved. As an illustration, results for 16 trace elements and preliminary interpretation are given for a series of pedologically important soil samples from Brasil.     

Multi-element analysis of urine by energy-dispersive x-ray fluorescence spectrometry

For multi-element analysis of human urine, 25-ml samples doped with yttrium as internal standard are evaporated gently and then ashed up to 460°C overnight. The residue is pelletized and analysed by energy-dispersive x-ray fluorescence. Acid addition to facilitate the digestion is not mandatory. Recoveries are nearly quantitative for traces of Fe, Ni, Cu, Zn and Sr, to a lesser extent for lead, but not for arsenic or selenium. The standard deviation per measurement is typically around 6%. The detection limits are such that some 10 elements can be determined simultaneously in normal urine, and possibly more in cases of importance to toxicology or industrial hygiene.     

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.     

Software package for quantitative analysis of solid materials by energy-dispersive x-ray fluorescence spectrometry without absolute calibration

A software package for quantifying elements in solids from energy-dispersive x-ray fluorescence data is described. The algorithm is based on the fundamental parameter approach and facilitates the simultaneous determination of several elements at widely varying concentrations. The software comprises three programs. One program, for spectrometer control and data acquisition, resides in a dedicated microcomputer. The two other programs, for spectra deconvulution and data evaluation, reside in a larger central computer. On-line communication between the computers is feasible, and the system facilitates the implementation of new improved programs. The performance of the system was tested on standard reference materials, and satisfactory accuracy was obtained for up to 21 elements.     

Comparison of two different approaches to calibrate an energy-dispersive x-ray fluorescence spectrometer for the analysis of aerosol-loaded filters

The quantitative analysis of aerosol loaded filters by x-ray fluorescence spectroscopy implies the use of calibration curves obtained from synthetic standards. Two preparation methods to obtain these calibration samples are described and compared, showing that matrix and enhancement effects are neglible for membranous filters and that both calibrations lead to acceptable results. Calibration standards produced via an aerosol generator always lead to a greater sensitivity compared to the standard produced with droplets. The filters resist the conditions of replicated measurements.     

Automated energy-dispersive X-ray fluorescence analysis of environmental samples

Summary A procedure is described for the routine automatic analysis of 20 elements in small environmental samples. Up to 50 samples a day can be processed. The instrument uses an energy dispersive X-ray spectrometer for the simultaneous detection of all elements during a 5–20 min measurement. Computer techniques are used for the subsequent data reduction of the X-ray spectra. The technique is applicable to air particulate matter filtered from the air, to suspended material in water which is filtered on a filter paper and to dissolved trace elements which are evaporated on filter paper or are collected on a thin ion-exchange loaded paper.

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Automatisierte energie-dispersive Röntgenfluorescenzanalyse von Umweltmaterial

Zusammenfassung Ein Verfahren zur automatischen Routinebestimmung von 20 Elementen in Umweltmaterial wird beschrieben. Bis zu 50 Proben je Tag können verarbeitet werden. Ein energie-dispersives Röntgenspektrometer wird zur simultanen Erfassung aller Elemente bei einer Messung von 5–20 min benutzt. Die nachfolgende Auswertung der Spektren wird mittels Computer durchgeführt. Das Verfahren findet Anwendung auf Schwebestaub oder in Wasser suspendierte Substanzen, die auf Filterpapier gesammelt wurden sowie auf gelöste Elementspuren, die auf Filterpapier getrocknet oder durch Ionenaustauschpapier angereichert wurden.

     

Comparison of two different approaches to calibrate an energy-dispersive x-ray fluorescence spectrometer for the analysis of aerosol-loaded filters

The quantitative analysis of aerosol loaded filters by x-ray fluorescence spectroscopy implies the use of calibration curves obtained from synthetic standards. Two preparation methods to obtain these calibration samples are described and compared, showing that matrix and enhancement effects are neglible for membranous filters and that both calibrations lead to acceptable results. Calibration standards produced via an aerosol generator always lead to a greater sensitivity compared to the standard produced with droplets. The filters resist the conditions of replicated measurements.     

Non-destructive analysis of archeological samples by energy-dispersive X-ray fluorescence

Summary A non-destructive method is described for the determination of major and minor constituents in archeological specimens by energy-dispersive X-ray fluorescence. Homogeneity tests are made by measuring at various sites of the specimen. In the same way, mean values are obtained for inhomogeneous specimen without taking samples. For calibration, powder standards are used. In case of the determination of elements with numbers up to 14 (Si) a vacuum chamber is used and the dimensions of the specimens are limited by the dimensions of that vacuum chamber, whereas for the determination of elements from K up to U specimens of any size, form or weight are suitable.

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Zerstörungsfreie Analyse von archäologischen Proben mit Hilfe der Energie-dispersiven Röntgenfluorescenzanalyse

Zusammenfassung Eine zerstörungsfreie Methode für die Bestimmung von Haupt- und Nebenbestandteilen in archäologischen Proben mit Hilfe der Energie-dispersiven Röntgenfluorescenzanalyse wird beschrieben. Für Homogenitätstests wird an mehreren Stellen der Probe gemessen. In der gleichen Weise werden für inhomogene Proben Mittelwerte erhalten ohne Probenahme. Für die Eichung werden Pulverstandards verwendet. Im Falle der Bestimmung von Elementen mit Ordnungszahlen bis 14 (Si) wird eine Vakuumkammer eingesetzt, und die Dimensionen der Proben sind durch die Dimensionen dieser Vakuumkammer begrenzt, während für die Bestimmung der Elemente K bis U Proben jeder Größe, jeder Form oder jeden Gewichts verwendbar sind.

     

Evaluation of multi-element analysis of blood serum by energy-dispersive x-ray spectrometry

Conventional energy-dispersive x-ray fluorescence is applied in the analysis of blood serum to give the concentrations of 7–10 elements simultaneously with minimal manipulation of the samples. Simple spotting onto a Mylar carrier of 250 μl of serum, doped with two internal standards, was chosen as the sample preparation step. Some 200 serum samples, analyzed in replicate (n = 2–6), were used to evaluate this procedure. The detection limits are 4 μg ml^-1 for K and Ca, 0.5–0.2 μg ml^-1 for Fe, Cu, Pb and Zn, and less than 0.1 μg ml^-1 for Se, Rb and Sr. Well above these limits, the standard deviation is around 10%. Comparison with the results of other measurements on the same samples indicates an accuracy of that order. The simplicity and high throughput, and the possibility of automating the x.r.f. measurements, make the proposed procedure suitable for screening large numbers of sera.     

Application of a fundamental parameter technique for solving peak-overlap problems in quantitative energy-dispersive x-ray fluorescence spectrometry

The procedure exploits the fundamental parameter technique for monoenergetic excitation. The algorithm describes each peak as a sum of line intensities, thus intensities from unresolved lines are included directly in the equations. The procedure includes the condition that the sum of all weight fractions equals unity, and so is valid only when all elements are measured by x-ray fluorescence spectrometry, e.g., in steel alloys. The procedure is tested with a set of theoretically calculated x-ray fluorescence intensities, and for two NBS standard steel alloys.     

Application of radionuclide sources for excitation in energy-dispersive X-ray fluorescence analysis

Summary X-ray fluorescence (XRF) analysis is in broad application in many fields of science where elemental determinations are necessary. Solid and liquid samples are analyzed by this method. Solids are introduced in thin or thick samples as melted glass, pellets, powders or as original specimen. The excitation of X-ray spectra can be performed by specific and polychromic radiation of X-ray tubes, by protons, deuterons, -particles, heavy ions and synchrotron radiation from accelerators and by -particles, X- and -rays and by bremsstrahlung generated by ^–-particles from radionuclide sources. The radionuclides are devided into groups with respect to their decay mode and the energy of the emitted radiation. The broad application of radionuclides in XRF excitation is shown in examples as semi-quantitative analysis of glasses, as quantitative analysis of coarse ceramics and as quantitative determination of heavy elements (mainly actinides) in solutions. The advantages and disadvantages of radionuclide excitation in XRF analysis are discussed.

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Anwendung von Radionuklidquellen zur Anregung in der Energie-dispersiven Röntgenfluorescenz-Analyse

Zusammenfassung Die Röntgenfluorescenzanalyse (RFA) ist auf all denen Gebieten der Wissenschaften verbreitet, in denen die Bestimmung der Elemente notwendig ist. Mit Hilfe dieser Methode können feste und flüssige Proben analysiert werden. Dünne oder dicke, feste Proben werden als geschmolzene Gläser, Tabletten, Pulver oder in Originalform eingesetzt. Die Anregung der Röntgenspektren erfolgt durch die spezifische und kontinuierliche Strahlung von Röntgenröhren, durch Protonen, Deuteronen, -Teilchen, schwere Ionen und Synchrotronstrahlung aus Beschleunigern und durch -Teilchen, Röntgen- und -Strahlung sowie durch von ^–-Teilchen erzeugte Bremsstrahlung von Radionuklidquellen. Die Radionuklide werden auf Grund ihrer Zerfallsart und auf Grund der Energie der emittierten Strahlung geordnet. Die breite Anwendung von Radionukliden für die Anregung bei der RFA wird an Hand von Beispielen wie der semiquantitativen Analyse von Gläsern, der quantitativen Analyse grober Keramik und der quantitativen Bestimmung schwerer Elemente (hauptsächlich der Aktinide) in Lösungen gezeigt. Die Vor- und Nachteile der RFA mit Radionuklidanregung werden diskutiert.

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Dedicated to Prof. Dr. K. H. Lieser on the occasion of his 65th birthday

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The author wishes to thank the Director of the Institute of Nuclear Chemistry at the Technische Hochschule Darmstadt, Prof. Dr. K. H. Lieser, for having the possibility to work in the field described in this paper.     

A fundamental parameters approach including scattered radiation for mono-energetically excited samples in energy-dispersive x-ray fluorescence spectrometry

A fundamental parameters approach that incorporates data on scattered radiation is shown to be a useful tool for the determination of trace elements in light matrices. For thick, transparent samples, a computer program is developed that uses differetial intensity equations adjusted for decreasing geometric efficiency. Various organic and biological reference materials are analysed to assess the reliability of the procedure. A nested design for analysis of variance shows that major errors can originate from the deconvolution process and sample inhomogeneities in many cases. For loose powders, great care must be exercised to avoid errors caused by scatter from the sample cups. The program is also useful for alloys.     

Use of sensitivity as a function of fluorescent x-ray energy in energy-dispersive x-ray spectrometry

The approximate linear relationship between the logarithm of the sensitivity and the logarithm of the energy of the observed characteristic x-ray emission is used to show the relative retention of elements during fusion with lithium tetraborate to form fused pellets, and the relative recovery of elements by preconcentration methods. Elements with atomic numbers ranging from 20 to 33 were investigated in fused pellets and/or filtered precipitated samples. Linear or nearly linear curves with slopes ranging from near two for infinitely thin samples to near six for infinitely thick samples are predicted if certain conditions of x-ray excitation are met.     

Tube-excited energy-dispersive X-ray fluorescence analysis. II. Energy-dispersive X-ray fluorescence analysis of air particulate material.

The use of monoenergetic exciting radiation of molybdenum obtained with a secondary target set-up, a conventional water-cooled tungsten anode x-ray tube and a Si(Li) semiconductor detector permits many trace and minor constituents from chlorine to strontium to be determined in particulate material collected on cellulose filters. The method is rapid and economical compared to other multielement techniques. The use of one or more single-element thin-film standards to calibrate for the analysis of many elements appears to be possible, but some systematic errors must be prevented. Absorption of the fluorescent radiation is remedied by a simple correction method. The precision and the accuracy of the method were critically examined by independent analysis of a number of samples with instrumental neutron activation analysis and by interlaboratory comparisons on the same samples.     

New possibilities of energy-dispersive X-ray fluorescence technique in the analysis of potable water

The article considers specific features of schemes of X-ray fluorescence analysis of liquid samples in the geometry of thick layers and in thin layers using the X-ray optics scheme with total internal reflection. A scenario is proposed for the analysis of liquid samples in thin layers using a simple X-ray optics scheme lowering the detection limits 1000-fold in comparison with the traditional scheme in thick layers. The internal standard method is implemented to improve the reproducibility of the results. The proposed scenario was tested in the analysis of potable water.     

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.