Determination of trace elements in Syrian medicinal plants and their infusions by energy dispersive X-ray fluorescence and total reflection X-ray fluorescence spectrometry

X-ray fluorescence (XRF) and total-reflection X-ray fluorescence (TXRF) techniques suited well for a multi-element determination of K, Ca, Mn, Fe, Cu, Zn, Rb, and Sr in some Syrian medicinal plant species. The accuracy and the precision of both techniques were verified by analyzing the Standard Reference Materials (SRM) peach-1547 and apple leaves-1515. A good agreement between the measured concentrations of the previously mentioned elements and the certified values were obtained with errors less than 10.7% for TXRF and 15.8% for XRF. The determination of Br was acceptable only by XRF with an error less than 24%. Furthermore, the XRF method showed a very good applicability for the determination of K, Ca, Mn, Fe, Cu, Zn, Rb, Sr, and Br in infusions of different Syrian medicinal plant species, namely anise (Anisum vulgare), licorice root (Glycyrrhiza glabra), and white wormwood (Artemisia herba-alba).     

XRF and TXRF techniques for multi-element determination of trace elements in whole blood and human hair samples

XRF and TXRF were established as useful techniques for multi-element analysis of whole blood and human head hair samples. Direct-XRF with different collimation units and different X-ray excitation modes was successfully used for the determination of S, P, K, Ca, Fe, and Br elements in blood samples and K, Ca, Mn, Fe elements in human hair samples. Direct analysis by TXRF was used for the determination of Rb and Sr in digested blood and human hair samples, respectively, while, the co-precipitation method using APDC for TXRF analysis was used for the determination of Ni, Cu, Zn, and Pb elements in both matrices. As a result, the improved XRF and TXRF methods were applied for multi-element determination of elements in whole blood and human hair samples in non-occupational exposed population living in Damascus city. The mean concentrations of analyzed elements in both matrices were on the reported range values for non-occupational population in other countries.     

Cold plasma ashing improves the trace element detection of single Daphnia specimens by total reflection X-ray fluorescence spectrometry

The recently developed dry method for the element determination of single freshwater microcrustacean specimens (Daphnia) using total reflection X-ray fluorescence (TXRF) spectrometry showed that inhomogeneities of the biological material on the glass carriers resulted in some cases in high background and hampered the detection of certain trace elements (e.g. Cr, Ni). The aim of this study was to test how inhomogeneities of the biological material can be reduced using cold plasma ashing (CPA) techniques. For that, single specimens of the microcrustacean Daphnia pulex prepared according to the dry method were measured by TXRF before and after CPA. To determine the efficiency of the removal of organic matrix, the background and signal-to-background relationship of 28 samples were analyzed. The results showed (1) a highly significant reduction of the background by CPA fluctuating between 26 and 46% (all elements) and (2) a significant increase of the signal-to-background relationship by the factor 1.5–2.5 (all elements) and a much better detection of Cr, Pb, As and Se. The element concentrations (with exception of Cr, Ni and Pb) after ashing were in the same range or slightly higher than that before ashing. No significant differences between the two treatments were observed for Mn, As, Pb, Se (November), Sr (November), Cr (March) and Pb (March). The element concentration of P, K, Ca, Cu, Zn, Cr (November), Fe and Rb were significantly higher after ashing. In general, they increased by 1.5–13.6% and were highest for Rb (March) and P (November). In contrast, the element concentration of Ni and Cr (only March) decreased significantly after ashing (Ni: 91.6–92.1%, Cr: 91.3%). We recommend the use of CPA for biological material in the microgram-range as a routine method for TXRF analysis, especially when trace elements in minute concentrations are of interest.     

Elemental content in deionized water by total-reflection X-ray fluorescence spectrometry

This study aimed to evaluate minor and trace elements in the water during different water purification steps of a deionized water production plant, located at CENA, by total-reflection X-ray fluorescence (TXRF) technique, using Ga as internal standard for elemental quantification. This approach was capable of determining Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, Se, Br, Rb at concentrations higher than 40–100 μg L⁻¹, and for K, Ca, Sc, Ti, V and Sr at concentrations higher than sub mg L⁻¹ in the water samples. TXRF spectrometer encompasses an X-ray tube with a Mo target with a Zr filter. The elemental characteristic X-rays were recorded by a Si(Li) semiconductor detector and the X-ray spectra deconvoluted by AXIL software.     

Quo Vadis total reflection X-ray fluorescence?

The multielement trace analytical method ‘total reflection X-ray fluorescence’ (TXRF) has become a successfully established method in the semiconductor industry, particularly, in the ultra trace element analysis of silicon wafer surfaces. TXRF applications can fulfill general industrial requirements on daily routine of monitoring wafer cleanliness up to 300 mm diameter under cleanroom conditions. Nowadays, TXRF and hyphenated TXRF methods such as ‘vapor phase decomposition (VPD)-TXRF’, i.e. TXRF with a preceding surface and acid digestion and preconcentration procedure, are automated routine techniques (‘wafer surface preparation system’, WSPS). A linear range from 10⁸ to 10¹⁴ [atoms/cm²] for some elements is regularly controlled. Instrument uptime is higher than 90%. The method is not tedious and can automatically be operated for 24 h/7 days. Elements such as S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Sn, Sb, Ba and Pb are included in the software for standard peak search. The detection limits of recovered elements are between 1×10¹¹ and 1×10⁷ [atoms/cm²] depending upon X-ray excitation energy and the element of interest. For the determination of low Z elements, i.e. Na, Al and Mg, TXRF has also been extended but its implementation for routine analysis needs further research. At present, VPD-TXRF determination of light elements is viable in a range of 10⁹ [atoms/cm²]. Novel detectors such as silicon drift detectors (SDD) with an active area of 5 mm², 10 mm² or 20 mm², respectively, and multi-array detectors forming up to 70 mm² are commercially available. The first SDD with 100 mm² (!) area and integrated backside FET is working under laboratory conditions. Applications of and comparison with ICP-MS, HR-ICP-MS and SR-TXRF, an extension of TXRF capabilities with an extremely powerful energy source, are also reported.     

Improvement of total reflection X-ray fluorescence analysis of low Z elements on silicon wafer surfaces at the PTB monochromator beamline for undulator radiation at the electron storage ring BESSY II

Several different total reflection X-ray fluorescence (TXRF) experiments were conducted at the plane grating monochromator beamline for undulator radiation of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II, which provides photon energies between 0.1 and 1.9 keV for specimen excitation. The lower limits of detection of TXRF analysis were investigated for some low Z elements such as C, N, O, Al, Mg and Na in two different detection geometries for various excitation modes. Compared to ordinary XRF geometries involving large incident angles, the background contributions in TXRF are drastically reduced by the total reflection of the incident beam at the polished surface of a flat specimen carrier such as a silicon wafer. For the sake of an application-oriented TXRF approach, droplet samples on Si wafer surfaces were prepared by Wacker Siltronic and investigated in the TXRF irradiation chamber of the Atominstitut and the ultra-high vacuum TXRF irradiation chamber of the PTB. In the latter, thin C layer depositions on Si wafers were also studied.     

Exchangeable fraction of elements in alluvial sediments under waste disposal site (Zagreb, Croatia)

Concentrations of Ag, Ba, Cd, Ce, Cs, Co, Cr, Eu, Fe, Rb, Sc, Sr, Th, and Zn exchangeable fractions were determined in alluvial sediments at waste disposal site area in the vicinity of water-well field. Samples have been leached with 0.5M NH₄Cl at a sample/solution ratio of 120 during 24 hours without shaking. INAA of dry NH₄Cl residues show that the concentrations of exchangeable elements determined in the most of the sediments below the wastes have natural levels. Ag, Ba and Sr are readily exchangeable; Rb, Cs and Zn have lower exchangeability, while Cd, Ce, Th, Sc, Eu, Cr, Fe and Co are rather immobile. Extremely high total and exchangeable silver concentration was found at 6.5–6.8 meters below waste in the aerated layer occasionally under the water table. Exchangeable concentrations in deeper water-bearing sediment layers are not elevated. Due to this, one can presume that the upper sediment layers act as chemical filter generally preventing the infiltration from overlying wastes into water-bearing layers.     

Determination of trace elements in bee honey,pollen and tissue by total reflection and radioisotope X-ray fluorescence spectrometry

Multielemental determinations in samples of various types of bee honey, pollen and bee tissue have been carried out using total reflection X-ray fluorescence spectrometry (TXRF) and radioisotope excited X-ray fluorescence spectrometry (XRF). The objective was to establish whether the elemental content of bee honey, in particular, correlates with any useful information about the environment, variety of honey, etc. An attempt has also been made to determine the X-ray techniques' ability to compete with atomic absorption spectrometry (AAS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES), with regard to elemental sensitivity, accuracy, sample preparation procedures, and in particular, economic performance, which is very important in selecting an appropriate technique for the analysis of large numbers of samples. The results confirm the advantages of the TXRF method for trace element analysis, but only when utilising monochromatic excitation and selecting a proper sample preparation procedure. The radioisotope XRF technique, which does not require any sample preparation, is still very competitive in analysis of elements with concentrations above a few ten ppm. Preliminary results also confirm some correlations between the elemental content of honey and the status of the environment, and encourage further work in this direction     

Direct analysis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders by total reflection X-ray fluorescence spectrometry

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al₂O₃ ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1–10 mg mL^–1 of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 g g^–1 as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 L of the 10 mg mL^–1 slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 m, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3–7 g g^–1 range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.Dedicated to the memory of Wilhelm Fresenius     

Radiochemical neutron activation analysis of Cs and Rb in geological samples using zeolite (clinoptilolite) chromatography and sodium tetraphenylborate precipitation

Three procedures for separating of Cs and Rb from geological samples were investigated. The fractional recovery was determined by radioactive tracers and by RNAA. In the first procedure 0.2 g of irrdiated sample is fused with Na₂O₂, acidified and passed through a clinoptilolite zeolite column. Cs and Rb were eluted with 7.5M HNO₃; chemical yields are in the range 93–98%. The second procedure is a supplement to the SUNDBERG and BOYNTON (1976) procedure; a previously discarded anion-exchanger effluent, containing Cs, Rb, Co, Na, etc., is passed through a clinoptilolite column. Cs and Rb are eluted with 7.5M HNO₃; yields are in the range of 82–94%. A third separation involves precipitation of Cs and Rb from the effluent and washings with sodium tetraphenylborate (NaBPh₄); yields are 64–83%.     

Total-reflection X-ray fluorescence imaging

A new experimental technique for surface imaging using total-reflection X-ray fluorescence (TXRF) is described. Although TXRF has so far been used to analyze the average chemical composition of rather large sample areas in the order of centimeters squared, a new opportunity to obtain spatial information has arisen through the combination of conventional TXRF and position-sensitive measurement using a collimator and a CCD camera. The most significant point here is that the extremely close detector sample geometry of TXRF measurement fits very well with the present imaging procedure. Scanning of the sample and/or incident beam is not necessary, and therefore the exposure time is reasonably short, typically 3–10 min. The number of pixels is approximately 1 million, and the spatial resolution obtained was several tens of microns in the present preliminary case. The selective-excitation capability of tunable monochromatic synchrotron radiation enhances the present imaging technique. Changing the energy of incident photons makes it possible to distinguish the elements, and one can obtain a surface image of the specific elements.     

Optimizing total reflection X-ray fluorescence for direct trace element quantification in proteins I: Influence of sample homogeneity and reflector type

Total reflection X-ray fluorescence (TXRF) is a very promising method for the direct, quick and reliable multi-elemental quantification of trace elements in protein samples. With the introduction of an internal standard consisting of two reference elements, scandium and gallium, a wide range of proteins can be analyzed, regardless of their salt content, buffer composition, additives and amino acid composition. This strategy also enables quantification of matrix effects. Two potential issues associated with drying have been considered in this study: (1) Formation of heterogeneous residues of varying thickness and/or density; and (2) separation of the internal standard and protein during drying (which has to be prevented to allow accurate quantification). These issues were investigated by microbeam X-ray fluorescence (μXRF) with special emphasis on (I) the influence of sample support and (II) the protein / buffer system used. In the first part, a model protein was studied on well established sample supports used in TXRF, PIXE and XRF (Mylar, siliconized quartz, Plexiglas and silicon). In the second part we imaged proteins of different molecular weight, oligomerization state, bound metals and solubility.     

Investigation of adsorbed mercury distribution in silver coated filters by X-ray fluorescence

We have been working on mercury collection from flue gas by amalgamation and subsequent XRF analysis. Previous results showed unexpectedly high relative standard deviation (30%) in collection efficiency when silver-coated filters were exposed to gas phase mercury in a pilot-scale test chamber. Filters were analyzed by micro-XRF, TXRF and conventional XRF to explore the source of scattering. It was concluded that mercury had inhomogeneously adsorbed in the filter as the cause of this variation, leading to a positive bias of 50% in efficiency value. Results reported in this paper suggest the TXRF method is accurate to within ±10% when X-ray counting statistics are not the limiting factor. Application of this filter in flue gas measurement will be presented.     

Total-reflection X-ray fluorescence analysis for semiconductor process characterization

Semiconductor process characterization techniques based on total-reflection X-ray fluorescence (TXRF) analysis are reviewed and discussed. One of the most critical factors in obtaining reliable determinations by TXRF is the reliability of the standard samples that are used. Conventional physisorption standard samples such as spin coat wafers have two potential drawbacks: reproducibility of depth profile and stability. A method of chemisorption called ‘immersion in alkaline hydrogen peroxide solution (IAP)’ was proposed that provides answers to these two problems. IAP standard samples were used to experimentally examine three methods of TXRF application: Straight-TXRF, VPD-TXRF, and Sweeping-TXRF. In the application of Straight-TXRF, the linearity of Cu at a level of 10⁹ atoms cm⁻² is examined. In the application of VPD-TXRF, test results of VPD-TXRF for both transition metals and light elements are shown. Finally, a new measurement protocol called Sweeping-TXRF is proposed to conduct whole-surface analysis without chemical preconcentration.     

Total reflection X-ray fluorescence analysis of fly ash from Bulgarian coal-fired power plants

The contents of Cl, Ca, K, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Rb, Sr, Ba and Pb in raw coal fly ash from five Bulgarian power plants were determined by total reflection X-ray fluorescence (TXRF), using gallium as the internal standard. The samples were analysed as in slurry form in Triton? X-114. The experimental parameters, such as grain size, concentrations of fly ash slurry and excitation time were optimised. For validation of the method, the certified reference material BCR-176R fly ash was used. The precision of the results obtained is characterised by a relative standard deviation of approximately 10%. The resulting data confirm the suitability of TXRF for the simultaneous determination of major, minor and trace elements in coal fly ash samples. Further advantages provided by TXRF are easy sample preparation (no sample dissolution) and the small sample amount required for analysis.     

Study on deposition kinetics of high-K materials by X-ray fluorescence techniques

X-ray fluorescence (XRF) techniques have been used to study, on different pretreated substrates, deposition kinetics of HfO₂ and Al₂O₃, two of the possible high-K materials under evaluation for future integration in microelectronic devices.X-ray fluorescence (XRF) and total X-ray fluorescence (TXRF) measurements demonstrate their capability to give useful information on the very initial growing cycles of deposition and on carbon and chlorine inclusion in the film. Moreover, XRF signal shows a good linear correlation with layer thickness for thick samples of both materials.     

Multielement analysis of standard reference materials with total reflection X-ray fluorescence (TXRF)

Summary X-Ray fluorescence analysis with total-reflected exciting beam (TRXF) represents a comparatively new development among the multielement methods. The main application of this method is the analysis of liquid samples. Furthermore, the measurements of suspensions and dust samples are practicable. With regard to sample preparation, execution and results information in various applications is at present available. This report gives a survey of advantages and restrictions of TXRF in soil science. After the digestion of various reference materials in two different ways, measurements were performed by TXRF. The elements Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Ba and Pb were taken into consideration.

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Multielement-Analyse von Standard-Referenzmaterialien mit der Totalreflexions-Röntgenfluorescenz (TRFA)

     

Multielement analysis by total reflection X-ray fluorescence spectrometry for the certification of lichen research material

 Total reflection X-ray fluorescence spectrometry was applied for the certification of IAEA lichen-336. The elements Ca, Mn, Fe, Cu, Zn, Rb, Sr and Pb were determined simultaneously. The concentrations range from 1.8 mg/kg for Rb to 2360 mg/kg for Ca. The results were compared with those of other methods and laboratories having participated in this certification for the International Atomic Energy Agency (IAEA): emission spectrometry, mass spectrometry, atomic absorption spectrometry, X-ray spectrometry, neutron activation analysis and voltammetry. The results determined by TXRF are in good agreement with the overall means of accepted values and differ from the means by 1 to 10%. Received: 1 September 1996/Revised: 15 October 1996/Accepted: 22 October 1996     

Recent trends in total reflection X-ray fluorescence spectrometry for biological applications

This review is focused on the application of total reflection X-ray fluorescence (TXRF) spectrometry in the field of biological research. In the last decade, most papers were published by authors who applied laboratory-scale TXRF equipments. The application of synchrotron radiation as excitation source (SR-TXRF) shows a slowly increasing tendency. In the cited papers the micro-, trace and multielement capability of these TXRF techniques was demonstrated in the clinical and medical laboratory practice, as well as in various plant physiological studies. For speciation of elements in biological matrices, the TXRF was used as element specific detector following an off-line separation step (e.g., thin layer chromatography, high performance liquid chromatography), however, these off-line methods are not competitive with the on-line coupled HPLC-inductively coupled plasma mass spectrometry.