Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Having established detection limits for transition elements exceeding current requirements of the semiconductor industry, our recent efforts at the Stanford Synchrotron Radiation Laboratory (SSRL) have focused on the improvement of the detection sensitivity for light elements such as Al. Data analysis is particularly challenging for Al, due to the presence of the neighboring Si signal from the substrate. Detection limits can be significantly improved by tuning the excitation energy below the Si–K absorption edge. For conventional TXRF systems this can be done by using a W–Mα fluorescence line (1.78 keV) for excitation. At a synchrotron radiation facility energy tunability is available. However, in both cases this results in a substantial increase in background due to resonant X-ray Raman scattering. This scattering dominates the background under the Al Kα fluorescence line, and consequently limits the achievable sensitivity for the detection of Al surface contaminants. In particular, we find that for a precise determination of the achievable sensitivity, the specific shape of the continuous Raman background must be taken into account in the data analysis. The data deconvolution presented here opens a new perspective for conventional TXRF systems to mitigate this background limitation. This results in a minimum detection limit of 2.4×10⁹ atoms/cm² for Al. Based on these results it will also be demonstrated that by improving the detector resolution, the minimum detection limit can be improved significantly. For a detector resolution of 15 eV as predicted for novel superconducting tunnel junction detectors, an improvement in minimum detection limit of approximately a factor of 3 can be estimated.     

Sub-picogram detection of lead by non-flame atomic fluorescence spectrometry with dye laser excitation

The frequency-doubled radiation of flashlamp-pumped dye laser has been compared with the radiation of an eleotrodeless discharge lamp (EDL) and a hollow cathode lamp (HCL) as excitation light sources in non-flame atomic fluorescence spectrometric (AFS) measurements. Detection limits and linear ranges of the analytical working curves have been studied. The aqueous Pb sample solutions used in this study were atomized in an electrically heated graphite rod. Direct line fluorescence at 405.8 nm has been observed. The limit of detection obtained with the laser as excitation source is about one order of magnitude lower than the detection limits obtained with the EDL and HCL. The absolute limit of detection of 0.2 pg is the lowest reported value to date attained in any atomic spectrometric method. The ultraviolet laser irradiance was found to be high enough to approach saturation conditions. As a result selfabsorption of the exciting laser beam is reduced and the linear range of the analytical working curve is extended to higher analyte concentrations.     

Analytical atomic spectrometry and imaging: Looking backward from 2020 to 1975

Some general aspects of the evolution of atomic spectrometry for chemical analysis over the period 1975 to now are described. Performance parameters such as detection limits and spatial analytical potential (lateral and depth resolution) are compared with the evolution of integrated circuit technology as described in Moore's Law. A few general trends of future development for the coming decade are postulated. Attention will be focused on analysis and imaging with beam techniques, especially secondary ion mass spectrometry and X-ray techniques on the basis of excitation with synchrotron radiation.     

Anregung von Spektren durch niederenergetischen Elektronenstoβ mit Anwendung als Lichtquelle für Spektralanalyse

Detection limits of atomic absorption spectroscopy (AAS) and atomic fluorescence spectroscopy (AFS) have been improved by the use of a King furnace. In atomic emission spectroscopy, however, the King furnace was hitherto used only in connection with thermal or RF excitation.The object of this work was to combine the advantages of the King furnace and the advantages of excitation by electron impact for AES. A light source based on a work by Ritschl in 1932 was built. The device consists of a King furnace for sample evaporation. Excitation of atoms is achieved by separate production and acceleration of electrons.The spectrochemical application of this excitation method was tested with Cd, Mg, Hg and B. Detection limits were measured and compared with those attained by other methods. Detection limits are better than those of comparable AES methods using thermal light sources. They compete favourably with those of AAS and AFS using a graphite crucible. The detection limit of Cd, for example, is 3·10^?13 g.The source was applied to determine traces in spectral graphite and to study the transport of material between the electrodes in high-voltage spark.     

Comparison of different excitation methods for X-ray spectral analysis: the case of synchrotron radiation

Different excitation means, protons, photons and electrons (PIXE, XRFA, and EPMA, respectively) have previously been compared with regard to the figures of merit, i.e. detection power, precision and accuracy. The aim in this article is to compare synchrotron radiation SR as another excitation method with the methods mentioned above. From this point of view the evaluation of (SR) was missing as an again independently optimized excitation method and was based as previously on practical problems of trace analysis, in this case on the determinations of traces in lead. The experiment has been performed with thick homogeneous samples of lead, the same samples already used in the former work, so that a direct comparison is possible. The calculation of the figures of merit is based on the measurements of the blank values and their relative standard deviation for the detection limit and on the random errors for the precision. Regarding the thick homogeneous target of lead XRFA still turns out to be the best method, whereas Synchrotron X-Ray Fluorescence SY-XRF compares favorably, at least for larger atomic numbers Z. Even PIXE is inferior to (SY-XRF) in the case of larger Z; when information on the lateral distribution of the elements is of interest, PIXE is indispensable.     

Comparison of different excitation methods for X-ray spectral analysis: the case of synchrotron radiation

Different excitation means, protons, photons and electrons (PIXE, XRFA, and EPMA, respectively) have previously been compared with regard to the figures of merit, i.e. detection power, precision and accuracy. The aim in this article is to compare synchrotron radiation SR as another excitation method with the methods mentioned above. From this point of view the evaluation of (SR) was missing as an again independently optimized excitation method and was based as previously on practical problems of trace analysis, in this case on the determinations of traces in lead. The experiment has been performed with thick homogeneous samples of lead, the same samples already used in the former work, so that a direct comparison is possible. The calculation of the figures of merit is based on the measurements of the blank values and their relative standard deviation for the detection limit and on the random errors for the precision. Regarding the thick homogeneous target of lead XRFA still turns out to be the best method, whereas Synchrotron X-Ray Fluorescence SY-XRF compares favorably, at least for larger atomic numbers Z. Even PIXE is inferior to (SY-XRF) in the case of larger Z; when information on the lateral distribution of the elements is of interest, PIXE is indispensable. Received: 13 June 2000 / Revised: 2 August 2000 / Accepted: 5 August 2000     

Preliminary investigation of a medium power argon radiofrequency capacitively coupled plasma as atomization cell in atomic fluorescence spectrometry of cadmium

The single ring electrode radiofrequency capacitively coupled plasma torch (SRTr.f.CCP) operated at 275W, 27.12 MHz and Ar flow rate below 0.7 lmin(-1) was investigated for the first time as atomization cell in atomic fluorescence spectrometry (AFS) using electrodeless discharge lamps (EDL) as primary radiation source and charged coupled devices as detector. The signal to background ratio (SBR) and limit of detection for Cd determination by EDL-SRTr.f.CCP-AFS were compared to those obtained in atomic emission spectrometry using the same plasma torch. The detection limit in fluorescence was 4.3 ngml(-1) Cd compared to 65 ngml(-1) and 40 ngml(-1) reported in r.f.CCP-atomic emission (AES) equipped with single or double ring electrode. The lower detection limit in EDL-SRTr.f.CCP-AFS is due to a much better SBR in fluorescence. The limit of detection was also compared to those in atomic fluorescence with inductively coupled plasma (0.4 ngml(-1)), microwave plasma torch (0.25 ngml(-1)) and air-acetylene flame (8 ngml(-1)). The influence of light-scattering through the plasma and the secondary reflection of the primary radiation on the wall of the quartz tube on the analytical performance are discussed. The non-spectral matrix effects of Ca, Mg and easily ionized elements are much lower in EDL-SRTr.f.CCP-AFS compared to SRTr.f.CCP-AES. The new technique was applied in the determination of Cd in contaminated soils, industrial hazardous waste (0.4-370 mgkg(-1)) and water (113 microgl(-1)) with repeatability of 4-8% and reproducibility in the range of 5-12%, similar to those in ICP-AES. The results were checked by the analysis of a soil and water CRM with a recovery degree of 97+/-9% and 98+/-4%, for a confidence limit of 95%. The present EDL-SRTr.f.CCP-AFS is a promising technique for Cd determination in environmental samples.     

Analysis of beers from Brazil with synchrotron radiation total reflection X-ray fluorescence

Summary In this study the concentrations of P, S, Cl, K, Ca, Mn, Fe, Zn and Br in twenty-nine brands of national and international beers were determined by synchrotron radiation total reflection X-ray fluorescence analysis (SR-TXRF). The results were compared with the limits established by the Brazilian legislation and the nutritional values established by National Agricultural Library (NAL, USA). The measurements were performed at the X-Ray Fluorescence Beamline at Brazilian National Synchrotron Light Laboratory, in Campinas, S?o Paulo, Brazil, using a polychromatic beam for excitation. A small volume of 5 ml of beers containing an internal standard used to correct geometry effects was analyzed without pretreatment. The measuring time was 100 seconds and the detection limits obtained varied from 1 mg ^. l^-1 for Mn and Fe to 15 mg ^. l^-1 for P.     

Laser excited atomic fluorescence of some transition elements in the nitrons oxide-acetylene flame

A pulsed, tunable dye laser, pumped with a nitrogen laser is used to excite the atomic fluorescence of Sc, V, Hf, Nb, Os, Zr, W, Rh and Ru. Except in the case of Rh, the nitrous oxide-acetylene flame has been used. The results obtained for Zr and W are due to scattering of the laser radiation from unvaporized particles in the flame. Since, for most elements, several fluorescence lines of comparable intensity have been observed after the primary excitation process, the usefulness of observing non-resonance fluorescence is stressed, particularly with regard to the possibility of minimizing spectral interferences. The experimental results demonstrate that the limits of detection obtained with the dye laser source are comparable or better than the best atomic absorption limits only when the same primary absorption line used for the atomic absorption measurements can be used for exciting the fluorescence.     

Zum heutigen Stand der spektrochemischen Spurenanalyse

Zusammenfassung Erniedrigung der Nachweisgrenzen und Ausweitung der Anwendungsmöglichkeiten bei Erhaltung der spezifischen Vorzüge der Spektral-analyse: kleine Probenmengen, gleichzeitige Bestimmung vieler Elemente, Analyse fester Proben ohne vorheriges Lösen, sind im allgemeinen das Ziel der Weiterentwicklung spektrochemischer Verfahren für die Spuren-analyse.Anhand der Stichworte Probenvorbereitung, Anregung, spektrale Zerlegung, Strahlungsmessung und Auswertung werden die in der letzten Zeit erzielten Fortschritte besprochen und der heutige Stand aufgezeigt.

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Summary In discussing the present state and future trends of spectrochemical trace analysis (atomic emission as well as absorption) the following topics are treated: sample preparation, light sources and excitation, spectral dispersion, radiation measurements, photometry and evaluation. Their influence on the limit of detection is shown. The gain in using suitable spectral apparatus and radiation receivers can be calculated or estimated and full use of the inherent possibilities can be made. In spite of good progress recently made such a complete knowledge of the influence of sample properties and excitation does not exist so far. With better understanding of these phenomena still lower limits of detection can be expected.

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In diesem Bericht sind auch gemeinsam mit anderen Mitarbeitern des Instituts für Spektrochemie in Dortmund angestellte Überlegungen verarbeitet.     

Evaluation of x-ray fluorescence spectrometry for the determination of platinum in catalysts and comparison with other spectrometric techniques

An x-ray fluorescence (x.r.f.) method is described for the determination of platinum contents (0.3–0.6%) in some special types of platinum catalysts. Calibration graphs were linear in the range 30–700 μg g^?1 platinum with a 3σ detection limit of 10 μg g^?1 for a 2000-s counting time. Because of the lack of certified standard platinum catalysts for checking accuracy, the results obtained were compared with results from visible spectrophotometry (tin (II) chloride method), optical emission spectrometry and atomic absorption spectrometry. Statistical evaluation showed no significant errors at the 95% confidence interval.     

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.     

The influence of X-ray resonant Raman scattering effects on the detection of copper(II) tetrasulphonated phthalocyanine (CuTSPc) thin-films deposited on gold electrodes

The influence of X-ray resonant Raman scattering on the detection capabilities of copper(II) tetrasulphonated phthalocyanine (CuTSPc) thin-films on gold electrodes has been investigated by means of synchrotron radiation X-ray fluorescence. In particular the paper focuses on the influence of the excitation energy in the relative narrow energy region of 9.2 to 11.7 keV on the detection limits and the peak-to-background ratios of copper.     

Measurement of trace element concentration in a metal matrix using total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence spectroscopy (TXRF) has been used in combination with synchrotron radiation in order to determine detection limits and lowest limits of concentration of trace elements in metal matrices. Two applications on irradiated material are described, where the TXRF method has some advantages, as compared to other detection methods, because only few micrograms of material is needed for the measurements. The first application is devoted to radiation damage studies on first wall material of future fusion reactors. Therefore, metal foils were irradiated with 590 MeV protons at PSI and the transmutational elements produced in the foils were measured. The second application is the assessment of radiation damage of core components in a nuclear power plant, e.g. the reactor pressure vessel. This is performed by the determination of the fast neutron fluence on the components using an activation reaction of ⁹³Nb which is a trace element in most reactor steels. Detection limits of a few picograms have been found in the experiments.     

An unusual systematic behaviour of detection limits for elements from 55Cs to 73Ta

A representative database for detection limits for all elements from ⁵⁵Cs to ⁷³Ta reveals that these limits are governed by a systematic zigzag pattern, according to which the odd atomic number elements have systematically lower detection limits than the even atomic number neighbour elements. This is true even when the actual detection limits vary by several orders of magnitude. We propose that such a systematic pattern be used as a requisite analytical criterion to evaluate the detection limit data, and any departure from this pattern be looked on with caution to check the analytical technique for any interference or matrix effect problems.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

原子发射光谱法中信背浓度比的推导与应用

基于原子发射光谱信号强度与CCD积分时间和样品浓度之间的线性关系, 推导并提出一种信背浓度比(SBCR)的新概念, 建立了检出限与SBCR之间的关系. 基于合理假设推导出最大积分时间、 最大信背比和最大信背浓度比等表达式, 并通过实验对模型进行了验证. 最后使用SBCR表征了低功率ArMPT对Cu元素的激发能力, 使其检出限由13.1 ng/mL降低至2.8 ng/mL.     

Comparison of synchrotron radiation total reflection X-ray fluorescence excitation–detection geometries for samples with differing matrices

The linear polarization of synchrotron radiation (SR) in the orbital plane leads to a background reduction in total reflection X-ray fluorescence (TXRF) analysis if a side-looking detector is used. The optimum orientation of the sample carrier in a SR-TXRF experiment, however, is determined by a trade-off between the exploitation of the linear polarization, the efficiency of excitation and the solid angle of detection and depends on the nature and size of the sample. SR-TXRF measurements on different sample types and using different reflector orientations have been carried out at the Hamburger Synchrotronstrahlungslabor bending magnet beamline L. A NIST standard water sample, a steel sample and an oil standard were analyzed with both a horizontal and a vertical sample carrier orientation. Strongly scattering samples led to lower detection limits with a horizontal reflector whereas weakly scattering samples showed lower detection limits with a vertical reflector configuration. On an intentionally contaminated wafer absolute detection limits of 6.6 fg for Ni could be extrapolated.     

Studies on Nuclear Resonant Scattering of Synchrotron Radiation by 40K

The studies on nuclear resonant scattering by ⁴⁰K using synchrotron radiation are reviewed. Brilliant and high pure synchrotron radiation permitted us to observe the nuclear resonant forward scattering by ⁴⁰K in a powdered KCl sample, the excitation of which is impossible with ordinary radioactive sources. Furthermore, nuclear resonant inelastic scattering of synchrotron radiation by ⁴⁰K in the KCl sample at room temperature has been measured using a high-resolution monochromator. Adding to these, from the excitation experiments of ⁴⁰K, the energy and lifetime of the first excited state of ⁴⁰K were confirmed. These measurements clearly show that the studies on the electronic states through hyperfine interactions and the dynamical properties of potassium atoms, which are very important in material science and biology, are possible. It should be noted that ⁴⁰K is the natural isotope of potassium and weakly radioactive. Our observation of forward and inelastic scattering of the radioactive nuclide ⁴⁰K will lead to further studies on other radioactive nuclides the resonant forward and inelastic scattering of which are not observed to date.     

Development of micro X-ray fluorescence spectrometer with multi excitation sources

X-ray fluorescence analysis (XRF) is a suitable technique for elemental analysis in nondestructive measurement. Recently, small area analysis by using the XRF technique has gained popularity. The synchrotron radiation source is responsible for the increase in the popularity of micro-XRF analysis. However, most people find it difficult to gain access to the synchrotron radiation facility. In this study, a micro-XRF system is developed for use in laboratories. To enable the use of this system, it is necessary to satisfy the following two conditions: (1) the excitation source must be optional for efficient excitation of the sample and (2) the X-rays must be focused. An X-ray tube with multi excitation sources has also been developed. In this tube, there are three targets, namely Cr, W, and Pd, on the anode, and each target can be excited sequentially. A doubly curved crystal (DCC) developed using a Si(111) crystal is used as the optics for focusing the X-rays into a beam with a diameter of less than 100 μm. A system composed of the X-ray tube and DCC optics is used to perform the small particle analysis of a Si wafer. The lower limit of detection (LLD) of the sample particle is estimated as 1.6 μm in diameter.     

Cadmium Determination in Sedimented Dust by Atomic Emission Spectrometry With a New Radiofrequency Capacitively Coupled Plasma Source

ABSTRACT

A new radiofrequency capacitively coupled plasma source (r.f.CCP) was used for Cd determination in dust samples by atomic emission spectrometry. The plasma torch consists of a molybdenum tube electrode and one or two ring electrodes situated outside the quartz tube. Plasma was operated at 27.12 MHz, at low power (275 W) and low gas consumption (0.4 1 min^? argon flow). The choice of the optimum operating conditions for Cd determination in dust samples dissolved in acids and pneumatically nebulized is presented. The results obtained in such samples were compared with those obtained by flame atomic absorption spectrometry (FAAS). The matrix effect of NaCl and CaCl₂ on Cd emission was also studied depending of the plasma coupling system. The true limit of detection for Cd in dust sample by r.f.CCP-AES is 3 μg g^?1. Concentration of Cd higher than 10 μg g^?1 can be determined by the proposed method with a relative standard deviation within the range 5 - 10%. The recovery is 100 ± 10%.