Synchrotron radiation total reflection X-ray fluorescence (SR-TXRF) for evaluation of food contamination

Summary The objective of this study was to use synchrotron radiation total reflection X-ray fluorescence analysis (SR-TXRF) for the determination of metals and other elements in food available to the population in commercial establishments, in order to evaluate the risks of contamination by these products. The analyzed species were vegetables, leafy vegetables, fruits, cereal and grain. The results indicated that some species were contaminated by Cr, Cu, Zn and Pb with concentrations much higher than the reference values.     

Multi-elemental analysis of produced water by synchrotron radiation total reflection X-ray fluorescence

The synchrotron radiation total reflection X-ray fluorescence (SRTXRF) technique was used for the analysis of heavy metals in produced water samples from oil field in Rio Grande do Norte, in order to determine potential sources of pollution. Since the inorganic components in produced water generally resembling sea water, pre-concentration procedures have been applied to increase the concentration of the analyte of interest and to minimize the salt matrix effects. This technique allows us to determine the contents of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Hg and Pb in 20 produced water samples. The great majority of the sampling points presented low elemental concentration value. However, in some sample, the Fe, Ni, Cu, Zn and Hg concentration were higher than the established limits by the Brazilian legislation.     

Monitoring of the environmental pollution by trace element analysis in tree-rings using synchrotron radiation total reflection X-ray fluorescence

This paper aims to study the environmental pollution in the tree development, in order to evaluate its use as bioindicator in urban and country sides. The sample collection was carried out in Piracicaba city, São Paulo State, which presents high level of environmental contamination in water, soil and air, due to industrial activities, vehicles combustion, sugar-cane leaves burning in the harvesting, etc. The species Caesalpinia peltophoroides (“Sibipiruna”) was selected because it is widely used in urban forestation. Synchrotron Radiation Total Reflection X-ray Fluorescence technique (SR-TXRF) was employed to identify and quantify the elements and metals of nutritional and toxicological importance in the wood samples. The analysis was performed in the Brazilian Synchrotron Light Source Laboratory, using a white beam for excitation and a Si(Li) detector for X-ray detection. In several samples, P, K, Ca, Ti, Fe, Sr, Ba and Pb were quantified. The K/Ca, K/P and Pb/Ca ratios were found to decrease towards the bark.     

Multielement determination in river-water of Sepetiba Bay tributaries (Brazil) by total reflection X-ray fluorescence using synchrotron radiation

Summary Trace elements were determined in the surface waters of tributaries of the Sepetiba Bay, Brazil (Piraquê, Itá, S?o Francisco, Guarda, Guandu Mirim, Vala do Sangue and Engenho Novo rivers) by total reflection X-ray fluorescence using synchrotron radiation (SRTXRF). Eighteen trace elements could be determined in the dissolved and the suspended particulate phases: Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr and Pb. The elemental concentration values were compared to the values recommended by the Brazilian legislation.     

Applications of total reflection X-ray fluorescence spectrometry in trace element and surface analysis

Total reflection X-ray fluorescence spectrometry (TXRF) is presented as a genuine surface analytical technique. Its low information depth is shown to be the characteristic feature differentiating it from other energy dispersive X-ray fluorescence methods used for layer and surface analysis. The surface sensitivity of TXRF and its analytical capability together with the limitations of the technique are discussed here using typical applications including the contamination control of silicon wafers, thin layer analysis and trace element determination. For buried interfaces and implantation depth profiles in silicon a combination of TXRF and other techniques has been applied successfully. The TXRF method has the particular advantage of being calibrated without the need for standards. This feature is demonstrated for the example of the element arsenic.     

Analysis of mineral water from Brazil using total reflection X-ray fluorescence by synchrotron radiation

The total reflection X-ray fluorescence using synchrotron radiation (SRTXRF) has become a competitive technique for the determination of trace elements in samples that the concentrations are lower than 100 ng ml⁻¹. In this work, thirty-seven mineral waters commonly available in supermarkets of Rio de Janeiro, Brazil, were analyzed by SRTXRF. The measurements were performed at the X-Ray Fluorescence Beamline at Brazilian National Synchrotron Light Laboratory (LNLS), in Campinas, São Paulo, using a polychromatic beam with maximum energy of 20 keV for the excitation. Standard solutions with gallium as internal standard were prepared for calibration of the system. Mineral water samples of 10 μl were added to Perspex sample carrier, dried under infrared lamp and analyzed for 200 s measuring time. It was possible to determine the concentrations of the following elements: Si, S, K, Ca, Ti, Cr, Mn, Ni, Cu, Zn, Ge, Rb, Sr, Ba and Pb. The elemental concentration values were compared with the limits established by the Brazilian legislation.     

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.     

A wavelength-dispersive arrangement for wafer analysis with total reflection X-ray fluorescence spectrometry using synchrotron radiation

Currently, the only apparent means to enhance the detection power of the TXRF technique would be to increase the intensity of the primary beam. Using synchrotron radiation, the most powerful X-ray source available, unfortunately, not only the fluorescence signal of the contaminant elements is increased, but also in equal measure, the intensities of the Si–K radiation from the wafer together with the scattered radiation. This results in an overloading of the energy-dispersive Si (Li) detector systems used hitherto, with the effect that the available primary intensity cannot be fully exploited. Wavelength-dispersive systems are free of such problems; they generate less detector background and can withstand higher count rates. Due to their small angle of acceptance, however, their detection efficiency is quite low. In this contribution we propose a wavelength-dispersive TXRF solution, which is optimized with regard to higher efficiency on the basis of large area multilayer mirrors in combination with a position-sensitive detector. The count rates in relation to energy-dispersive instruments and the energy resolution of the new system have been calculated using ray-tracing techniques.     

Recent results of synchrotron radiation induced total reflection X-ray fluorescence analysis at HASYLAB,beamline L

At the Hamburger Synchrotronstrahlungslabor (HASYLAB), Beamline L, a vacuum chamber for synchrotron radiation-induced total reflection X-ray fluorescence analysis, is now available which can easily be installed using the adjustment components for microanalysis present at this beamline. The detector is now in the final version of a Vortex silicon drift detector with 50-mm² active area from Radiant Detector Technologies. With the Ni/C multilayer monochromator set to 17 keV extrapolated detection limits of 8 fg were obtained using the 50-mm² silicon drift detector with 1000 s live time on a sample containing 100 pg of Ni.Various applications are presented, especially of samples which are available in very small amounts: As synchrotron radiation-induced total reflection X-ray fluorescence analysis is much more sensitive than tube-excited total reflection X-ray fluorescence analysis, the sampling time of aerosol samples can be diminished, resulting in a more precise time resolution of atmospheric events. Aerosols, directly sampled on Si reflectors in an impactor were investigated. A further application was the determination of contamination elements in a slurry of high-purity Al₂O₃. No digestion is required; the sample is pipetted and dried before analysis. A comparison with laboratory total reflection X-ray fluorescence analysis showed the higher sensitivity of synchrotron radiation-induced total reflection X-ray fluorescence analysis, more contamination elements could be detected. Using the Si-111 crystal monochromator also available at beamline L, XANES measurements to determine the chemical state were performed. This is only possible with lower sensitivity as the flux transmitted by the crystal monochromator is about a factor of 100 lower than that transmitted by the multilayer monochromator. Preliminary results of X-ray absorption near-edge structure measurements for As in xylem sap from cucumber plants fed with As(III) and As(V) are reported. Detection limits of 170 ng/l of As in xylem sap were achieved.     

Trace analysis of high-purity iron by total reflection X-ray fluorescence spectrometry

Summary A combined procedure enabling simultaneous multielement analysis of trace impurities in high-purity iron is presented. After removal of the iron matrix by solvent extraction with methyl isobutyl ketone, the trace elements Ti, V, Cr, Mn, Ni, Cu, Pb and Bi are determined by means of total reflection X-ray fluorescence analysis. Detection limits are found in the range of 100 ng/g. The reliability of the method is verified by the analysis of commercial high-purity iron and by the comparison of analytical data obtained by ICP-AES.     

Trace analysis of high-purity copper by total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence (TXRF) analysis after the separation of matrix element was studied for the determination of trace impurity elements (Ca, Sc, V, Cr, Mn, Fe, Co, Ni and Zn) in high purity copper. Matrix copper was removed by electrolysis (0.2 A, 8 h) of a nitric acid solution. A 10 μL aliquot of the remaining solution of the electrolysis was dropped on a silicon-wafer sample-carrier and dried in a vacuum. This was repeated five times and the precipitate of five 10 μL-aliquots was analyzed by TXRF using a W-Lβ beam with an incident angle of 0.05?°. TXRF analytical values were obtained by using relative sensitivity factors of the analytes to the internal standard element (Pd). Detection limits of the analytes ranges from 0.077 ng for Zn to 0.785 ng for Ca.     

Trace analysis of high-purity copper by total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence (TXRF) analysis after the separation of matrix element was studied for the determination of trace impurity elements (Ca, Sc, V, Cr, Mn, Fe, Co, Ni and Zn) in high purity copper. Matrix copper was removed by electrolysis (0.2 A, 8 h) of a nitric acid solution. A 10 μL aliquot of the remaining solution of the electrolysis was dropped on a silicon-wafer sample-carrier and dried in a vacuum. This was repeated five times and the precipitate of five 10 μL-aliquots was analyzed by TXRF using a W-Lβ beam with an incident angle of 0.05 °. TXRF analytical values were obtained by using relative sensitivity factors of the analytes to the internal standard element (Pd). Detection limits of the analytes ranges from 0.077 ng for Zn to 0.785 ng for Ca. Received: 25 December 1997 / Revised: 30 March 1998 / Accepted: 2 April 1998     

Determination of technetium by total reflection X-ray fluorescence

The measurement of technetium in inorganic solutions is reported for the first time using total reflection X-ray fluorescence (TXRF). Sodium pertechnetate solutions eluted from decayed ⁹⁹Mo generators were efficiently excited with a silver-anode X-ray tube in a standard configuration. The technique has been developed to aid establishing the extent of stoichiometric relations between Tc and a ligand in organo-metallic compounds synthesized with diagnostic purposes for nuclear medicine. The precision attained was 5% and the detection limit achieved for Tc in inorganic solutions by TXRF at 1000 s was 0.039 μg/ml.     

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)

     

Nonaqueous suspensions in total reflection X-ray fluorescence analysis of solids

It has been suggested to use suspensions of solid samples in viscous liquids for the determination of the elemental composition by the total reflection X-ray fluorescence (TRXF) method. Two liquids—ethylene glycol and glycerol—have been studied as a dispersion phase. It turned out that the sedimentation stability of suspensions in these liquids is higher than in water. During 5 min of sedimentation, the suspended analyte concentration changes by 10–15 rel. % in nonaqueous media and by up to 50 rel. % in aqueous media. It has been determined that the repeatability of measurements in nonaqueous suspensions is 3–5 rel. % against 10–15 rel. % for aqueous suspensions. It has been demonstrated that ethylene glycol and glycerol can be efficiently used for preparing samples for the TRXF method.     

Element determination in medieval soil samples by total reflection X-ray fluorescence analysis

An aqua regia extraction procedure for heavy metals in soils optimised for total reflection X-ray fluorescence analysis is presented. The procedure is applied to 92 soil samples of medieval layers from the city area of Dortmund. Sixteen elements (P, S, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Ag, Sn, and Pb) were used to characterise 17 sample sites. The results are projected onto the medieval urban structure of Dortmund. Two sites loaded with non-ferrous heavy metal could be detected and correlated with archaeological data. The efficiency and repeatability of the proposed extraction procedure is discussed.     

Trace element determination in thorium oxide using total reflection X-ray fluorescence spectrometry

Applicability of Total Reflection X-ray Fluorescence (TXRF) spectrometry for the determination of trace metals at concentration of µg/g level in thorium oxide was studied. The TXRF spectrometer was calibrated using a multielement standard solution and the method was validated by analyzing another multielement standard solution. Sample preparation conditions were optimized for the TXRF determinations of trace metals in thorium oxide. The elements K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Ba and Pb present in thorium oxide standards were determined after dissolving them in HNO₃/HF mixture and separating the bulk matrix, thorium, by solvent extraction using tri-n-butyl phosphate (TBP) and tri-n-octyl phosphine oxide (TOPO) as extractants. A comparison of TXRF determined concentrations of trace elements Ca, V, Cr, Mn, Fe, Ni and Cu with the certified values shows that TXRF determined concentrations have an RSD of 20% (1 s for n = 4) and are within an agreement of 20% of the certified values in most of the cases.     

Surface analysis for Si-wafers using total reflection X-ray fluorescence analysis

Summary Total Reflection X-Ray Fluorescence Analysis is presented as a novel analytical tool for the determination of metal impurities on Si-Wafer surfaces [1]. This method allows accurate quantification of surface coverages down to 10¹¹ atoms/cm² in a non-destructive way. The technique uses a molybdenum tube, a Si(Li) detector, and instrumentation for the exact control of the angle of incidence which must be set to a particular value below the cricitical angle for total reflection with an accuracy better than 0.1 mrad. Advantages are the lack of sample preparation and vacuum. Standards for quantification can be easily produced. Repeatability tests on three different wafers show good variability even for low concentrations.

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Oberflächenanalyse für Si-Wafer mit Hilfe streifend einfallender Röntgenstrahlen

     

Direct elemental analysis of cancer cell lines by total reflection X-ray fluorescence

The elemental content of Cu, Fe and Zn in two human adenocarcinoma cell lines was investigated by total reflection X-ray fluorescence (TXRF) spectrometry. Cancer cells were sedimented directly to the quartz plates using a modified cytospin slide holder setup. Special glass stands and caps were also constructed to hold the quartz plates with the cells during the vapour-phase microwave assisted digestion. The method was validated by analysis of certified reference materials. The signal-to-noise ratio was optimized by washing the cells with different solutions. The technique was applied to the determination of Cu, Fe and Zn content of HT-29 and HCA-7 colorectal adenocarcinoma cell lines. Dry mass of the centrifuged cells were determined and the elemental analysis data reported for the two cell lines were referred either to cell numbers, to the total protein content or to the dry mass.