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.     

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.     

High-precision energy-dispersive x-ray fluorescence analysis of manganese in ferromanganese

A high-precision x-ray fluorescence method for the determination of manganese in ferromanganese is described. The method involves excitation of the sample with a ¹⁰⁹Cd isotopic source and measurement with a high-resolution Si(Li) detector. To preserve the optimal energy resolution even at high count rates, the system incorporates a pulsed optical feedback preamplifier and a pulse pile-up rejector. The rejected pulses are corrected for by means of an adequate live-time correction circuit. Processing of the spectra is accomplished with the aid of a digital computer. The relative precision of the method is approximately 0.2%.     

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.     

Multi-element determination of dissolved heavy metal traces in sea water by total-reflection x-ray fluorescence spectrometry

Dissolved heavy metal traces in sea water are determined by a procedure based on total-reflection x-ray fluorescence spectrometry (t.x.r.f.). The trace elements are separated from the salt matrix by chelation with sodium dibenzyldithiocarbamate, selective chromatographic adsorption of the metal complexes onto a lipophilized silica-gel carrier, and subsequent elution of the metal chelates by a chloroform/methanol mixture. Aliquots of the eluate are then dispensed onto highly polished quartz sample carriers and evaporated to thin films for the t.x.r.f. measurements. The following elements can be determined: V, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, Cd, (Hg), Pb, and U. For 200-ml samples and a measuring time of 1000 s, detection limits of 5–20 ng kg^?1 are achieved for most of these elements. The limits are slightly higher for iron, zinc and mercury because of fluctuations in the blank values. Systematic investigations of the yield in the separation and enrichment step are described, and the procedure is characterized with regard to blanks, detection limits, precision and accuracy. The accuracy was checked with the aid of the sea-water reference material NASS-1. Some applications to Baltic sea water and open ocean waters are reported and discussed in terms of their information content.     

Multi-element analysis of urine by inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry

This work shows the analytical potential of inductively coupled plasma orthogonal-acceleration time-of-flight mass spectrometry (ICP-OA-TOF-MS) for rapid, simultaneous, and reliable determination of more than 50 elements at ultra-trace levels in urine. Under optimum instrumental conditions, after a 10-fold sample dilution step, and by using Rh as an internal standard, ICP-OA-TOF-MS also enables the determination of elements whose assay is more diffcult when using conventional quadrupole instruments. This is confirmed by the analysis of commercially available reference urine samples and/or by analytical recoveries study and isotope ratio based determination of accuracies. On the other side, the interference resulting from polyatomic carbon, chlorine, or various sulfur species does not allow the determination of elements such as Cr, Fe, V, Se and As without a mathematical correction.

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.     

Multi-element analysis by energy-dispersive X-ray fluorescence using a simple calibration procedure, requiring only one or two standards

Summary A reliable method for the determination of the slopes of calibration curves by interpolation is described for multi-element analysis by energy-dispersive X-ray fluorescence. The method is based on normalizing theoretically calculated curves of slope vs. atomic number, with the aid of one or two standards. It is applied to the analysis of powdered samples, using correction via the Comptonscattering peak to compensate for small matrix effects.

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Multielementanalyse durch energiedispersive Röntgenfluorescenz mit einem einfachen Eichverfahren, das nur ein oder zwei Standards erfordert

Zusammenfassung Eine zuverlässige Methode für die Bestimmung der Steigungen der Eichkurven für die Multielementanalyse durch energiedispersive Röntgenfluorescenz wird beschrieben. Die Methode basiert auf der Normierung theoretisch berechneter Kurven für die Abhängigkeit der Steigung von der Ordnungszahl mit Hilfe von ein oder zwei Standards. Sie wird angewendet auf die Analyse von Pulverproben unter Benutzung der Compton-Streupeak-Korrektur zum Ausgleich kleinerer Matrixeffekte.

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On leave from Rand Afrikaans University, Johannesburg, Republic of South Africa     

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.     

Analysis of Jamaican soils and sediments by energy-dispersive X-ray fluorescence spectrometry

The calibration of a tube excited Energy-Dispersive X-Ray Fluorescence spectrometer for routine geochemical analyses of Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Rb, Sr and Pb in Jamaican soils and sediments is described. Simple linear and parabolic regression models using scattered radiation and an element as internal standards were applied. The analysis of over 200 samples from a regional soil survey has been used to contribute to a database on the geochemistry of Jamaican soils and sediments. An application example of the Zn distribution map in Jamaican soils is presented.     

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.     

Determination of dissolved arsenic in waters at μg l−1 levels by precipitation and energy-dispersive x-ray fluorescence spectrometry

Arsenic is precipitated as magnesium ammonium arsenate with magnesium ammonium phosphate as carrier. The precipitate is collected on a glass-fibre filter and arsenic is measured by energy-dispersive x-ray fluorescence spectrometry with a silver secondary target. With 200-ml water samples and 100-s counting times, the limit of detection is 0.7 μg As l^?1. The method is applicable to all types of natural water including sea waters.     

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.     

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.     

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.

     

Simultaneous determination of sixteen major and minor elements in river sediments by energy-dispersive x-ray fluorescence spectrometry after fusion in lithium tetraborate glass

Fluvial sediments, including the NBS SRM-1645 Standard River Sediment, were fused in lithium tetraborate to form glass discs on which determinations of 16 elements (K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr and Pb) were obtained simultaneously at a single set of x-ray conditions by energy-dispersive x-ray fluorescence spectrometry (e.d.x.r.f.). Relatively high sample-to-flux ratios of 1:3 were employed to obtained determinations of several minor as well as major elements on a single disc. Lower sample concentrations 1:6 and 1:10 were also used with the NBS SRM-1645. Inter-element corrections for absorption by iron were significant for detectable elements heavier than iron. In the NBS SRM-1645 samples, corrections were made for the fluorescence of chromium by the Fe K lines as well as the absorption of the Fe K lines by chromium. A background correction was also necessary for manganese in NBS SRM-1645. At the lowest sample-to-flux ratio (1:10) good agreement was obtained between the e.d.x.r.f. determinations and the NBS values for all quantifiable elements except zinc. At higher sample-to-flux ratios, agreement with the NBS values was generally poorer with increasing sample concentration. The relative standard deviation (RSD) of the eight quantifiable major and minor elements (K, Ca, Ti, Mn, Fe, Zn, Sr and Zr) determined under a single set of x-ray conditions ranged from 2 to 9% (RSD) with a mean RSD of 4.4% for a set of replica discs fused with Lake Pueblo/Arkansas River sediment samples.     

Dilution method in x-ray fluorescence spectrometry

The Lachance-Traill method was modified to a dilution method that retains all the advantages of the original method plus it enables the determination of as many elements as one pleases and is far simpler mathematically. The method had been tested with determination of copper, molybdenum, zinc, and arsenic in copper intermediates.     

Determination of total sulphur in coal by x-ray fluorescence spectrometry

A precise x-ray fluorescence method for the determination of sulphur in coat. The sample is mixed with calcium oxide and active carbon and is gradually heated to 900°C. After coding, lithium tetraborate and lead oxide are added and a prepared. The Pb M_α line is used as an internal standard for the KK_α line. The results for coal have a relative standard deviation of approximately 1% and exhibit.