Optimization of the signal-to-background ratio in energy-dispersive X-ray fluorescence analysis using a Si(Li) detector

A mathematical model of an energy dispersive X-ray fluorescence spectrometer is discussed based on the analysis of the processes of radiation transport in the sample and in the detector and electron transport in the detector. The results of calculations performed according to the proposed model were compared with the available experimental data. The effect of the parameters of primary X-radiation and the detector’s thickness on the signal-to-background ratio was calculated. It was shown that with a change of the primary radiation source and the detector’s thickness, the signal-to-background ratio of the analytical signal varied by several orders of magnitude.     

A miniaturized fluorescence detector with a windowless flow cell using a light-emitting diode.

A miniaturized fluorescence detector using a high-brightness light-emitting diode as an excitation source was constructed and evaluated. A windowless flow cell based on a commercial four-port cross fitting was designed to reduce the stray-light level and to eliminate the optical alignment. The observed detection limit for fluorescein was 26 nM in the continuous-flow mode. The error in the reproducibility of the responses was evaluated by the FIA method, and was found to be within 2% RSD.     

Microanalysis of methotrexate by high-performance liquid chromatography using a fluorescence detector

Methotrexate (N¹⁰-methyl-4-aminofolic acid) has been determined by HPLC after oxidizing it with permanganate to a fluorogenic derivative. The detection limit has been 0.01 g/ml. The method has been applied for the determination of methotrexate in blood serum of rats.     

Estimation of the properties of an energy-dispersive X-ray fluorescence spectrometer based on a composite double-layer detector

A mathematical model of double-layer Si-Ge and Si-AsGa energy-dispersive detectors of X-rays based on the analysis of processes of radiation and electron transfer in the detector is proposed along with a model of an energy-dispersive X-ray fluorescence spectrometer on the basis of this detector. The probabilities of recording of photons in different sections of the detector response function are calculated using the Monte-Carlo technique. It is shown that, in using an anticoincidence circuit and a Si detector as the first layer and Ge or AsGa detectors as the second layer, a detector with improved characteristics can be obtained, namely, the suppressed loss peaks of Ge or As and Ga and the efficiency of detection at the high radiation energy close to that of the Ge or AsGa detector. This detector in the energy-dispersive X-ray fluorescence spectrometer in some cases allows the reduction of the background level.     

Characterization of the flow of anisotropic colloidal particles using energy-dispersive X-ray diffraction

The technique of energy-dispersive X-ray diffraction to study the orientation of microscopic crystalline particles dispersed in a liquid has been described recently. This complements previous neutron diffraction studies by permitting measurements at higher spatial resolution. Work with synchrotron radiation and high-energy X-rays has allowed studies on liquid dispersions flowing in pipes with a thickness of about 1 cm and a spatial resolution of 100 mum. Kaolinite is often found as a dispersion of monocrystalline, microscopic plates. The crystallographic layer structure is commensurate with the particle shape: the 00l direction is normal to the plane of the plates. Measurements of diffraction of the flowing liquid dispersion in a pipe oriented in various directions to the incident beam can be used to deduce the average orientation and order parameters of the particles. The competing effects of alignment with walls and in flow fields were observed. Further work has measured the orientation near a bend in a pipe.     

X-ray spectrometry using polycapillary X-ray optics and position sensitive detector

Polycapillary X-ray optics (capillary X-ray lens) are now popular in X-ray fluorescence (XRF) analysis. Such an X-ray lens can collect X-rays emitted from an X-ray source in a large solid angle and form a very intense X-ray microbeam which is very convenient for microbeam X-ray fluorescence (MXRF) analysis giving low minimum detection limits (MDLs) in energy dispersive X-ray fluorescence (EDXRF). A new method called position sensitive X-ray spectrometry (PSXS) which combines an X-ray lens used to form an intense XRF source and a position sensitive detector (PSD) used for wavelength dispersive spectrometry (WDS) measurement was developed recently in the X-ray Optics Laboratory of Institute of Low Energy Nuclear Physics (ILENP) at Beijing Normal University. Such a method can give high energy and spacial resolution and high detection efficiency simultaneously. A short view of development of both the EDXRF using a capillary X-ray lens and the new PSXS is given in this paper.     

A windowless flow cell-based miniaturized fluorescence detector for capillary flow systems

A miniaturized fluorescence detector utilizing a three-dimensional windowless flow cell has been constructed and evaluated. The inlet and outlet liquid channels are collinear and are located in the same plane as the excitation paths, while the optical fiber used to collect the emission light is perpendicular to this plane. The straightforward arrangement of the flow path minimizes band dispersion and eliminates bubble formation or accumulation inside the cell. The use of high-brightness light-emitting diodes (LEDs) as the excitation source and a miniaturized metal package photomultiplier tube (PMT) results in a compact and sensitive fluorescence detector. The detection limit obtained from the system for fluorescein isothiocyanate (FITC) in flow injection mode is 2.6 nmol/L. The analysis of riboflavin and FITC by packed capillary liquid chromatography is demonstrated.      

Qualitative identification of alloys by energy-dispersive X-ray spectroscopy

Energy dispersive X-ray spectroscopy can be used to identify alloy types quickly and, in many cases, to distinguish between alloy systems within a certain alloy type. Characteristic X-rays of major components in an alloy are produced through excitation by an isotopic source. Ratios of the X-ray intensities of a pair of elements are plotted vs. ratios of the theoretical weight fractions of these elements. This provides a unique data point which is a function of the composition of the particular alloy system. In some cases, characteristic X-rays of minor constituents are used for total identification.     

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.

     

Development of an X-ray detector using surface plasmon resonance

A new X-ray detector using surface plasmon resonance (SPR) is proposed. The detector consists of a prism coated with a thin metal film and semiconductor film. Optical laser pulse induces SPR condition on the metal surface, and synchronized X-ray pulse which is absorbed into the semiconductor film can be detected by measuring the change of the resonance condition of the surface plasmon. The expected time and spatial resolution of this detector is better than that of conventional X-ray detectors by combining this SPR measurement with ultra-short laser pulse as the probe beam. Our preliminary investigation using Au and ZnSe coated prism implies this scheme works well as the detector for the ultra-short X-ray pulse.     

Thermal analysis of ammonium nitrate by energy-dispersive X-ray diffraction

Ammonium nitrate was heated and cooled in consecutive steps in a high temperature device mounted on a X-ray goniometer. Diffraction patterns were measured at each temperature, using a Si-Li detector together with a multichannel analyzer. The results strongly support the existence of a phase II'. They show that the phase change IV/III goes via a transition state similar to or consistent with phase II'.

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Zusammenfassung Ammoniumnitrat wurde in einer Hochtemperaturkammer auf einem Röntgengoniometer schrittweise aufgeheizt und abgekühlt. Bei jeder Temperatur wurde ein Beugungsdiagramm aufgenommen mit einem Si-Li-Detektor und angeschlossenem Vielkanalanalysator. Die Ergebnisse unterstützen die Annahme einer Phase II'. Sie zeigen, daß die Phasenumwandlung IV/III über einen Übergangszustand verläuft ähnlich oder identisch mit der Phase II'.

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Résumé Le nitrate d'ammonium était chauffé et refroidi pas à pas dans un four fixé sur un goniomètre de rayons X. A chaque température, des diagrammes de diffraction étaient mesurés par un détecteur semiconducteur, combiné avec un sélecteur multicanaux. Les résultats supportent l'existence d'une phase IF. Ils montrent, que la transition des modifications IV/III procède par une phase de transition, qui ressemble à la phase II'.

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, . , Si-Li . II. , IV/III , II.

     

Simultaneous acquisition of X-ray spectra using a multi-wire, position-sensitive gas flow detector

A multi-wire, gas-filled position-sensitive detector has been developed for the simultaneous recording of wavelength-dispersed X-ray signals that enables X-ray fluorescence spectrometry with a limited multi-element capability in the low Z element range. Details of the modular construction of the detector are given. The detector performance was characterized using Al–K radiation and a variable slit system. The detector has been applied in a laboratory spectrometer equipped with an electron source and a double multilayer mirror device as the wavelength-dispersing element. Spectra from Al and Si obtained in the simultaneous acquisition mode show good agreement with calculations performed using a ray-tracing model.     

Determination of metal components in marine sediments using energy-dispersive X-ray fluorescence (ED-XRF) spectrometry

A rapid energy-dispersive X-ray fluorescence (ED-XRF) spectrometric method for the analysis of metal components of marine sediments has been presented. Calibrations were made using synthetic matrix. The agreement of the results for sediment standard reference materials with reference values is satisfactory. Major advantages of the non-destructive ED-XRF technique over conventional chemical digestion methods include the applicability to analyzing the major oxide components, as well as to trace metals, and the avoidance of hazardous chemicals. The method has been applied to the routine analysis of Hong Kong marine sediment.     

Online monitoring of aerosols with an energy-dispersive X-ray spectrometer

A continuously working sampling and analyzing device was developed and tested. It is suitable for monitoring of metals bound to particulate matter in emissions of stack gases. The samples were precipitated on a pure quartz fiber filter tape and analyzed shortly afterwards non-destructively by an energy dispersive X-ray spectrometer (EDXRS). By using this method a wide range of elements with atomic numbers from 19 (K) ¶to 82 (Pb) can be analyzed. New experiments have shown that the novel combined particle sampling and analysis system ¶(X-DUST) could also successfully be used for the monitoring of toxic elements in ambient air.     

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.

     

Online monitoring of aerosols with an energy-dispersive X-ray spectrometer

A continuously working sampling and analyzing device was developed and tested. It is suitable for monitoring of metals bound to particulate matter in emissions of stack gases. The samples were precipitated on a pure quartz fiber filter tape and analyzed shortly afterwards non-destructively by an energy dispersive X-ray spectrometer (EDXRS). By using this method a wide range of elements with atomic numbers from 19 (K) to 82 (Pb) can be analyzed. New experiments have shown that the novel combined particle sampling and analysis system (X-DUST) could also successfully be used for the monitoring of toxic elements in ambient air.     

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     

固定化脂肪酶活性的X射线微区分析

利用X射线微区分析的方法，对吸附交联法得到的固定化脂肪酶的微观活性进行了分析。结果表明：以合成出的大孔吸附树脂为固定化酶栽体，酶活较高，活性脂肪酶分布较均匀。并得到了固定化脂肪酶的活性定位的最佳条件。     

Standardless energy-dispersive X-ray fluorescence analysis using primary radiation monochromatized with LiF(200) crystal

Energy-dispersive X-ray fluorescence spectrometer (EDXRF) with primary radiation monochromatized by LiF(200) crystal was developed. In the constructed spectrometer, the radiation from the Ag target X-ray tube operated at 50 kV and 40 mA excites the secondary target (Cu, Se, Zr or Mo). The characteristic radiation (Cu K_α, Se K_α, Zr K_α or Mo K_α) of the target is monochromatized with LiF(200) crystal and excites elements in the analyzed sample. The X-ray spectra are collected by thermoelectrically cooled Si-PIN detector with resolution of 145 eV at 5.9 keV. The pinhole collimator placed in front of the X-ray detector allows reducing size of the analyzed area. Quantitative analysis is performed using standardless fundamental parameters (FP) method. Because sample is excited using highly monochromatized radiation, the calculations are much simpler and analysis error resulting from uncertainty of X-ray tube spectral distribution is completely eliminated. Moreover, EDXRF system allows obtaining very low background and appropriate secondary target can be selected for the best excitation of the determined elements and to avoid overlapping of the analyte peaks with characteristic radiation originating from the secondary target. The FP calculations were verified using several certified reference materials of stainless steel. The spectrometer was used for nondestructive analysis of mono- and polycrystals of selenide spinels of general formula M_xN_yCr_zSe₄ (where M, N are Cu²⁺, Zn²⁺, Cd²⁺, Mn²⁺, Ge²⁺, Ni²⁺, V³⁺, Sb³⁺, Ga³⁺). The results from EDXRF were compared with those obtained by means of the wavelength-dispersive X-ray fluorescence spectrometry (WDXRF).