Total Reflection X-ray Fluorescence Spectrometry Research Articles

Direct analysis of blood serum by total reflection X-ray fluorescence spectrometry and application of an artificial neural network approach for cancer diagnosis

Iron, copper, zinc and selenium were determined directly in serum samples from healthy individuals ( n=33) and cancer patients ( n=27) by total reflection X-ray fluorescence spectrometry using the Compton peak as internal standard [L.M. Marcó P. et al., Spectrochim. Acta Part B 54 (1999) 1469–1480]. The standardized concentrations of these elements were used as input data for two-layer artificial neural networks trained with the generalized delta rule in order to classify such individuals according to their health status. Various artificial neural networks, comprising a linear function in the input layer, a hyperbolic tangent function in the hidden layer and a sigmoid function in the output layer, were evaluated for such a purpose. Of the networks studied, the (4:4:1) gave the highest estimation (98%) and prediction rates (94%). The latter demonstrates the potential of the total reflection X-ray fluorescence spectrometry/artificial neural network approach in clinical chemistry.

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 α 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.

Analysis of low Z elements on Si wafer surfaces with synchrotron radiation induced total reflection X-ray fluorescence at SSRL, Beamline 3-3: comparison of droplets with spin coated wafers

The unique properties of synchrotron radiation, such as high incident flux combined with low divergence, its linear polarization and energy tunability, make it an ideal excitation source for total reflection X-ray fluorescence (TXRF) spectroscopy in order to non-destructively detect trace impurities of transition metals on Si wafer surfaces. When used with a detector suitable for the determination of low energy radiation this technique can be extended to the detection of low- Z elements, such as Al, Na and Mg. Experiments have been performed at SSRL Beamline 3-3, a bending magnet beamline using monochromatic radiation from a double multilayer monochromator. The wafer was mounted vertically in front of the detector, which was aligned along the linear polarization vector of the incoming synchrotron radiation. This configuration allows the detector to accept a large solid angle as well as to take advantage of the reduced scattered X-ray intensity emitted in the direction of the linear polarization vector. A comparison between droplet samples and spin coated samples was done, in order to compare the capabilities of vapor phase decomposition (VPD-TXRF) with conventional SR-straight-TXRF. Detection limits in the range of 50 fg corresponding to 2E10 atoms/cm 2 have been obtained for Na. The spin coated samples, prepared from solutions containing an equal amount of Na, Mg and Al showed an unexpected result when performing a scan of the angle of incidence of the incoming X-rays suggesting a different adsorption behavior of the elements in a multielement solution on the wafer surface. The observation of this behavior is important because the spin coating technique is the standard method for the preparation of surface standards in semiconductor quality control. This effect could be characteristic of the Na, Mg, Al solution used, but the angle dependence of the fluorescence signal of a standard should always be investigated before using the standard for calibration of the apparatus and quantification.

Depth profiles of shallow implanted layers by soft ion sputtering and total-reflection X-ray fluorescence

A new method suitable for depth profiling of shallow layers on different materials is presented. It is based on a soft and planar ion sputtering combined with differential weighing, total-reflection X-ray fluorescence (TXRF) spectrometry and Tolansky interferometry. By means of a stepwise repetition of these techniques it is possible to determine both density/depth and concentration/depth profiles. The respective quantities are expressed in terms inherent only to the sample and traceable to the SI-units or subunits gram, nanometer and mole. It is a unique feature of this method that density/depth profiles can directly be obtained from measurements without any calibration or theoretical approximation. The method is applied to a Si wafer implanted with Co ions of 25 keV energy and a nominal dose of 1×10 16 cm −2. The depth resolution is shown to be <3 nm while a total depth of some 100 nm can be reached. The concentration/depth profile is compared with RBS measurements, wet-chemical etching plus TXRF and Monte Carlo simulations. In view of the fact that only similar but not exactly the same samples have been examined by these methods, a good correspondence can be noticed.

Biomonitoring of trace elements in muscle and liver tissue of freshwater fish

The aim of this study was to investigate the potential impact of a coal combustion power plant in the northern part of Vietnam with regard to elemental pollution on the surrounding environment. Freshwater fishes ( Clarias fucus) were sampled both at a site exposed to the emissions of the power plant and at a reference site seemingly free from industrial activities. The elemental concentrations in muscle and liver tissue were analyzed using total-reflection X-ray fluorescence and atomic absorption spectroscopy. A comparison of muscle tissue with International Standards (Food and Agricultural Organization) showed that the fishes from both sites did not constitute any health risk for human consumers with regard to the elements Cu, Zn, As, Se, Cd, Pb and Cr. Generally, concentration differences between sites were found to be small in the edible tissue. Compared to the muscle tissue, concentrations of metals were elevated in the liver. The elemental concentrations of P, S, K, Ca, Fe, Mn, Zn and Pb were significantly higher in the hepatic tissue from the exposed site, suggesting—together with measurements of airborne pollutants—emissions from the power plant as a probable source of these elements.

Determination of trace elements in planktonic microcrustaceans using total reflection X-ray fluorescence (TXRF): first results from two Chilean lakes.

First results are described from the application of a recently developed dry method for determination of elements in single specimens of freshwater microcrustaceans, using total reflection X-ray fluorescence spectrometry (TXRF). This method is a powerful, non-destructive technique for quantifying the trace element content of minute biological samples with a dry weight of 3-50 microg. Three different freshwater microcrustaceans were sampled, from the natural, uncontaminated Lake Laja and from the artificial Rapel reservoir which is slightly contaminated by drainage water from a copper mine. Single specimens of Daphnia pulex, Bosmina chilensis, and Ceriodaphnia dubia were prepared using a modification of the dry method and measured by TXRF. The results showed that both As, Mn, Fe, Ni, Zn, and Cu content and the bioaccumulation of these metals were usually significantly different between the microcrustaceans from the two lakes. The largest difference was found for Cu which was eight times more concentrated in the two microcrustaceans from Rapel reservoir than it was in D. pulex from Lake Laja.

Seasonal variations in diurnal concentrations of trace elements in atmospheric aerosols in Chicago

Atmospheric aerosols are solid or liquid particles dissolved in air, which can change their chemical composition frequently depending on various parameters such as wind speed and direction. In this study, diurnal atmospheric aerosol filter samples, taken at Loyola University Chicago’s Air Monitoring Station, are discussed with respect to variations in trace elemental composition at different seasons. The samples collected, were digested in a microwave oven and analyzed by total reflection X-ray fluorescence (TXRF) spectrometry. To aid interpretation of the samples, meteorological parameters were recorded and back trajectory analysis was employed. Four days, based on average meteorological conditions, were selected for each season as example to obtain preliminary insight into trace elemental variations. The results indicate that elemental concentrations vary during seasons and depend on major wind patterns (speed and direction). The differences were most pronounced in summer, where most elemental concentrations were found to be lowest of all seasons due to onshore (east) wind from Lake Michigan, depriving the air parcel of larger particles by deposition into the lake. In spring and fall the elemental concentrations determined were much higher, which can be attributed to the prevailing and often stronger westerly winds and associated higher particle freight. In winter the situation can be described as intermediate between summer and spring/fall with moderate elemental concentrations due to weaker winds and less stable wind directions.

Study of biofilm formation by total-reflection X-ray fluorescence spectrometry

A total reflection X-ray fluorescence spectrometric method was developed for elemental analysis of natural biofilms grown on polycarbonate substrates in the Lake Velence. For the duration of 9 weeks long growing period, two substrates were removed weekly from the lake and investigated by analytical and algological methods. The total biomass production achieved its highest value after 7 weeks. Ca, Sr and Ti, as well as Fe, Mn, K and Zn showed their maximum concentrations in the biofilms after 5 and 6–7 weeks, respectively. The enrichment factors of the 6 weeks old biofilm for the detected seven elements amounted to 10 3–10 4. The recommended colonization time for biomonitoring of the Lake Velence is 6 weeks applying polycarbonate substrates.

Analysis of depth profile for impurity concentration in Si wafer by synchrotron radiation excited total reflection X-ray fluorescence spectroscopy

SR-TXRF spectroscopy is one of the powerful methods of measuring surface and near surface wafer contamination. To measure the depth profile of impurity concentration, Ni and Fe spin coated Si wafers and their annealed wafers have been measured by SR-TXRF. The depth profiles of impurity concentration are determined by comparing the angular dependence of fluorescence intensities calculated from possible models with measured intensities. These experiments are the applications of SR-TXRF angle scan for quantitative depth profiling of impurity concentration in the range of a few hundred angstrom depth without using any destructive method.

On-line preconcentration flow system for multi-elemental analysis by total reflection X-ray fluorescence spectrometry

A scaled-down preconcentration flow system coupled with total reflection X-ray fluorescence spectrometry is proposed for the simultaneous determination of Co, Cu, Mn, Ni, Pb and Zn. The flow system, assembled with an 11-μl column of AG50W-X8 resin and three-way solenoid valves commanded by a computer program, permits the automatic preconcentration, addition of internal standard (Ga) and the deposition of the eluate on the reflector plate. Interferences due to Na and Ca were evaluated. When compared with conventional flow systems, the proposed approach allows a significant reduction in the consumption of eluent (200 μl per determination) and only 1075 μl of sample is required to obtain enrichment factors of approximately 20. Detection limits of Co, Cu, Mn, Ni, Pb and Zn were improved 11, 13, 13, 12, 17 and 14 times, respectively. The proposed system was applied to analyze human saliva and river water samples. Analysis of a Natural Water Standard Reference Material-1640 (Natural Institute of Standard and Technology) showed excellent agreement with certified values. The recoveries for Co, Cu, Mn, Ni, Pb and Zn in a spiked saliva sample were between 64 and 108%.

A new approach for archaeological ceramics analysis using total reflection X-ray fluorescence spectrometry

The purpose of this study is to investigate the use of a new quantitative analysis method in case total reflection X-ray fluorescence (TXRF) is applied to archaeological ceramics. This method is alternative to and simpler than traditional TXRF quantitative analysis or typical techniques of elemental analysis such as atomic emission and absorption spectrometry (AES and AAS) which implies the chemical digestion of the sample. A new procedure which allows to obtain an homogeneous sample has been successfully applied. This way it was possible to obtain quantitative results for the elements present in the sedimentation obtained from a suspension prepared with the ceramic sample, by resorting to addition of an internal standard. The archaeological ceramic shards have been also chemically digested and analyzed by inductively coupled plasma-atomic emission spectrometry, AES with flame atomization and electrothermal atomic absorption spectrometry. The quantitative data obtained by means of both TXRF, AAS and AES were compared and worked out by multivariate statistical techniques, such as principal components analysis and hierarchical cluster analysis in order to achieve information concerning pottery provenance.

Copper exposure modifies the content and distribution of trace metals in mammalian cultured cells.

With this work, we have determined the cellular content of Cu, Fe and Zn in different cell lines, by using total reflection X-ray fluorescence spectrometry (TXRF). In addition, we examined whether cellular exposure to 100 micromoles l(-1) of Cu-His modifies the intracellular content and distribution of these trace metals. Our results indicate that all the cell lines displayed the same pattern of relative intracellular abundance of trace metals (Cu<Fe<Zn). This pattern shifted to Fe<Zn<Cu, when extracellular copper concentration was increased. In HepG2 and Caco2 cells, copper exposure increased intracellular copper content while Fe and Zn decreased. Regarding cellular distribution of trace metals, they decreased in the cytosol fraction of HepG2 cells, after exposure to copper. Therefore, our results indicate that cellular adaptation to copper involves a new balance in the relative abundance of trace metals and induces changes in the cellular distribution of Cu, Zn and Fe.

Specimen Handling, Data Treatment and Leverage

ISOTC (Technical Committee) 201 was organized in 1992 to establish the International Standard on surface analysis methods such as Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS), Glow Discharge Optical Emission Spectroscopy (GDOES) and Total Reflection X-ray fluorescence Spectroscopy (TXRF). ISO TC 201 on Surface Chemical Analysis consists of eight Sub-Committees and one Working Group (WG) at present. The activities of Sub-Committee 2 (SC 2) and Sub-Committee 3 (SC 3) are deliberation and establishment of the International Standard on General Procedure, and Data Management and Treatment, respectively. “ISO 14976: Surface chemical analysis—Data transfer format” was enacted as the International Standard in 1998, “ISO 14975: Surface chemical analysis—Information formats” was in 2000. These two standards were discussed in SC 3. Specimen handling, reference materials and reporting data have been on the table in SC 2 but International Standard has not yet been adopted. ISO 14976 and ISO 14975 were translated into Japanese to be adapted in JIS. In this report the two International Standards are explained and the trend of standardization in SC 2 and SC 3 as well as practical use of International Standard is briefly touched.

Flow-injection preconcentration and graphite furnace atomic absorption spectrometric determination of platinum

Flow-injection graphite furnace atomic absorption spectrometric (GFAAS) methods were worked out using oxime, sulphoxine and 2,2′-diamino-diethylamine (DEN) cellulose microcolumns for preconcentration of platinum after reduction by iodide or sulphite ions. The detection limits were, at 20-fold enrichment, 0.21, 0.18 and 0.30 μg l −1, respectively. The total reflection X-ray fluorescence spectrometry (TXRF) was also used for the determination of platinum in eluates. The method was applied for the determination of platinum in salmeterol xinafoate and Ca-folinate pharmaceutical compounds. Decomposition of organic matrix of Ca-folinate was necessary before the preconcentration.

Study of monolayer dispersion of MoO3 on muscovite powder and diffusing behavior of MoO3 on muscovite wafer by SR-TXRF

The dispersion capacity of MoO3 on the surface of muscovite powder was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The results indicated that MoO3 can disperse onto the surface of a support as a sub-monolayer. The dispersion capacity was 5.88 mg MoO3 (g muscovite)−1, or 3.24 Mo atoms nm−2. The diffusing process of MoO3 on muscovite wafer was investigated by means of Synchrotron Radiation excited Total-reflection X-Ray Fluorescence spectroscopy (SR-TXRF). A stripe of MoO3 on the muscovite wafer was used as the diffusion source. After thermal treatment in air or dry N2, MoO3 diffuses onto the surface of muscovite and forms a sub-monolayer. Sublimation of MoO3 was also detected during the diffusion process. The diffusion rate in two heating atmospheres differed significantly. The diffusion rate of MoO3 on muscovite in dry N2 was greater than that in air. A possible explanation of the phenomena is that surface diffusion onto the muscovite surface plays a more important role in the process than transportation via gas phase during the diffusion of MoO3.

A correlation of TOF-SIMS and TXRF for the analysis of trace metal contamination on silicon and gallium arsenide

Both time-of-flight secondary ion mass spectrometry (TOF-SIMS) and total reflection X-ray fluorescence spectroscopy (TXRF) are widely used tools in the semiconductor industry. They are variously used to support R&D, product development, production, quality control and failure analysis. With increasing demands for cleanliness and contamination control in both the semiconductor and compound semiconductor industries, enhanced sensitivity and capabilities are required from existing analytical techniques. This paper will detail the cross correlation of TOF-SIMS and TXRF for the analysis of trace elemental contaminants on both Si and GaAs wafers. Close agreement will be demonstrated between both techniques. Additionally, the quantitative mapping of Cu and Zn on GaAs using TOF-SIMS will be demonstrated.

Trace Elemental Analysis of Drugs of Abuse Using Synchrotron Radiation Total Reflection X-Ray Fluorescence Analysis (SR-TXRF)

Synchrotron radiation total reflection X-ray fluorescence spectroscopy (SR-TXRF) was utilized to analyze various trace elements in small amounts of drugs of abuse. Sample amounts of 1 microL solutions containing 10 microg of drugs (methamphetamine, amphetamine, 3,4-methylenedioxymethamphetamine, cocaine, and heroin) were spotted on silicon wafers for direct analysis. In addition, a leaflet of marijuana was set directly on a silicon wafer, and opium in the form of a soft lump was smeared on another silicon wafer for analysis. In these experiments, about 10 pg of contaminant elements could be detected. For example, in a seized methamphetamine sample, iodine was found, which could be indicative of synthetic route. In seized 3,4-methylenedioxymethamphetamine samples, variable amounts of phosphorus, calcium, sulfur, and potassium were found, which could not be detected in a control 3,4-methylenedioxymethamphetamine sample. For marijuana and opium, two spectral patterns were obtained that were far different from each other and could be easily discriminated. Using SR-TXRF, pg amounts of each trace element in 10 microg of various drugs can be easily detected, which is not the case either for a standard TXRF experimental system or for other elemental analysis techniques.

DETERMINATION OF SOME TRACE ELEMENTS IN MINERAL SPRING WATERS BY TOTAL REFLECTION X-RAY FLUORESCENCE SPECTROMETRY (TXRF)

ABSTRACT Trace metal concentrations of mineral spring waters in central Anatolia, Turkey were investigated by total reflection X-ray fluorescence spectrometry (TXRF). The concentrations of trace heavy-metal ions were quantitatively determined with an internal Ga standard. The element concentrations obtained by TXRF are comparable to results obtained by graphite furnace absorption spectrometry (GFAAS) after separation-preconcentration on an Amberlite XAD-4 column and inductively coupled plasma-mass spectrometry (ICP-MS).

Whole-surface analysis of semiconductor wafers by accumulating short-time mapping data of total-reflection X-ray fluorescence spectrometry.

Total-reflection X-ray fluorescence (TXRF) spectrometry with no chemical preconcentration, often called "straight-TXRF", is now widely used in the semiconductor industry. The small detection area of TXRF enablesmapping measurement of contamination of the semiconductor surface, which is very useful in process characterization. However, the small detection area had been believed to limit rapid whole-surface analysis. Contrary to this general understanding, in this study we demonstrated that a new method, called "sweeping-TXRF", which is essentially short-time multipoint mapping by straight-TXRF, can rapidly provide an average concentration. A considerable problem of this method is the contribution of errors in glancing angle and areal element distribution to the fluorescence. Using statistics, we examined the errors and demonstrated that most of them are canceled and are not significant in actual semiconductor applications. The results of an experiment that measured localized 6 x 10(10) atoms cm(-2) nickel contamination supported the above conclusion. Applying sweeping-TXRF to existing TXRF instruments is easy-the only requirement is a small software modification. We believe that sweeping-TXRF will be utilized for rapid whole-surface analysis in many fields, especially in the semiconductor industry.

Development and application of a micro-digestion device for elemental analysis of biological samples

A commercially available piece of equipment for high pressure ashing was adapted for the digestion of micro-samples of biological origin by a supplementary device. This attachment is shown to be suitable for solids with a sample amount of some micrograms and for liquids with a volume of a few microliters. In addition, the homogeneity of two reference materials NBS SRM 1571 “Orchard Leaves” and BCR CRM 414 “Plankton” is tested. For that purpose, the results of elemental analysis of small portions down to the level of 1 mg are compared with those for larger portions recommended by the supplier. Elements are found to be homogeneously distributed in test portions down to 100 mg but a few elements show an inhomogeneous distribution in portions ≤3 mg. For multi-element determinations, total reflection X-ray fluorescence spectrometry was used after addition of an internal standard to the digestion solutions.