Total Reflection X-ray Fluorescence Spectrometry Research Articles

Trace Metals in Microcrustaceans and Brazilian Waterweed from a Contaminated Chilean Wetland Using Total Reflection X-Ray Fluorescence Spectrometry

The trace element content of individual copepod specimens and of the Brazilian water weed (Egeria densa) from a metal-contaminated wetland in Southern Chile were determined using total reflection X-ray fluorescence spectrometry. Sampling of the water and the organisms was carried out at three sampling sites during 2004. Enhanced concentrations of dissolved Fe and Mn were found in the column water and in the pore water. The Fe content in the benthic copepods was significantly elevated compared to other aquatic organisms from different Chilean lakes. Regarding E. densa, healthy (green coloured) plants showed mass fractions of Fe, Mn, Ni, Cu and Zn which were typical for uncontaminated systems. In contrast, damaged (brownish coloured) plants exhibited very high Fe and Mn concentrations indicative of contamination or processes which changed the element load from the environment to the plant.

Electrodeposition and dissolution of yttrium-hexacyanoferrate layers

The electrodeposition and dissolution of yttrium-hexacyanoferrate [YHCNFe(II)] were investigated by electrochemical quartz crystal microbalance technique (EQCM). The electrodeposition was carried out by potential cycling or stepping from solutions of Y(NO 3) 3 and K 3[Fe III(CN) 6] of different concentrations. The ratio of the reactants was also varied. No deposition was found in dilute solutions ( c < 10 −3 mol dm −3). The increase of concentrations led to an intense deposition of YHCNFe(II) in the course of reduction of [Fe III(CN) 6] 3−. At high concentrations of the reactants a coagulation deposition of YHCNFe(III) at open-circuit has also been detected. During the reduction the first phase is the nucleation which requires saturation or oversaturation in respect to the reacting species near the gold surface. The growth phase is much faster than the formation of nuclei, and its rate depends on the concentration and the concentration ratio of the species. The composition of the deposits has been determined by total reflection X-ray fluorescence (TXRF) spectrometry. From the molar ratio of atomic constituents (K, Y and Fe) of the slightly soluble deposit (solubility: 5 × 10 −5 mol dm −3) formed after reduction of Fe(III) a formula K 0.46Y 1.18[Fe II(CN) 6] can be derived. This value is in good accordance with the molar mass calculated from the results of EQCM experiments which also revealed that the deposit contains ca. 2 mol H 2O/mol YHCNFe(II). The solubility of YHCNFe(III) is substantially higher ( s = 2 × 10 −3 mol dm −3), and according to the results of TXRF measurements, its composition is Y[Fe III(CN) 6]. The reoxidation of YHCNFe(II) takes place in two steps. The first one is a partial oxidation which is accompanied by the desorption of K + ions from the layer. During further oxidation a fast dissolution occurs due to the high solubility of YHCNFe(III).

Radioassay of prominent Nigerian fossil fuels using gamma and TXRF spectroscopy

Radioassay of the established fossil fuels found in Nigeria has been carried out using a combination of gamma and total reflection X-ray fluorescence (TXRF) spectrometry. Results indicate that of the three fossils, bitumen with a total of 61.54±23.93 Bq kg −1 has the highest natural radioactivity. This is followed by coal with a total of 30.48±5.29 Bq kg −1 . The mean natural radioactivity 0.06±0.025 Bq kg −1 measured in the crude oil samples is quite low compared to those determined for the other two fossils. Of the three fossil fuels, coal displayed the highest potential of containing most of the elements analyzed for while bitumen and crude oil indicate As, Ca, Cr, Fe, K, Mn, Ti, V and Cr, Fe, Mn and V, respectively, at detectable levels. Most of these elements except As, Co, Cr and V are crustal or lithophilic and are therefore expected to be present at higher concentrations in coal and bitumen samples in view of their higher soil content. The elements Ni, Cu, Zn, Pb and S are fingerprint elements for crude oil and are therefore necessary to be detected in such and related bitumen samples.

Total reflection X-ray fluorescence spectrometry for the introduction of novel materials in clean-room production environments

In this paper, a number of case studies on the analysis of novel metallic contaminants on conventional and alternative substrates using the technique of total reflection X-ray fluorescence spectrometry (TXRF) is presented. Investigated materials include Si and Ge substrates, high-/spl kappa/ dielectric contaminants, and layers, and Si wafers contaminated with elements from metal gates and Cu interconnects. One focus is on the application and optimization of detection limits in direct TXRF. For the TXRF analysis of contaminants on Si wafers, a general conclusion is that a combination of three excitation sources is needed to cover the whole range of interest: a low-energy excitation (about 5 keV, e.g., WM/spl alpha/, Cr K/spl alpha/) for the low Z elements such as Na, Mg, and Al, a moderate-energy excitation (10-20 keV, e.g., WL/spl beta/, MoK/spl alpha/) for the 3d-transition elements, and a high-energy excitation (25-35 keV, e.g., W, continuum) for the analysis of elements such as Zr, Ru, Mo, and Pd. Also, for the analysis of novel substrates using direct TXRF, a careful selection of the excitation source results in better detection limits. In this way, detection limits at 10/sup 10/-10/sup 11/ at/cm/sup 2/ can be achieved, even for novel contaminants and substrates. As the International Technology Roadmap for Semiconductors (ITRS) requires control below 5/spl times/10/sup 9/ at/cm/sup 2/, the application of a preconcentration procedure such as vapor phase decomposition-droplet collection TXRF (VPD-DC-TXRF) is required. Proper use of this procedure allows the improvement of the detection limits by two to three orders of magnitude, depending on wafer size and chemical collection efficiency. The usability of this preconcentration procedure in combination with TXRF will be demonstrated for noble elements and germanium substrates.

The Role of Atomic Spectrometric Techniques in the Determination of Chemical Elements in Atmospheric Aerosols

This review covers the application of atomic and mass spectrometric techniques for the determination of metals and metalloids in atmospheric aerosols. Atomic spectrometric methods based on flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), atomic fluorescence spectrometry (AFS), total reflection X-ray fluorescence (TXRF) spectrometry and plasma based techniques such as inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICPMS) are reviewed, because a considerable amount of research is presently performed in this field. The application of atomic and mass spectrometric techniques for fractionation studies based on the use of chemical sequential extractions for metal partitioning in airborne particulate matter and fly ashes are also discussed. This survey contains; 156 references and covers mainly the literature published over the last decade.

Isolation, Catalytic Properties, and Competitive Inhibitors of the Zinc-Dependent Murine Glutaminyl Cyclase

Murine glutaminyl cyclase (mQC) was identified in the insulinoma cell line beta-TC 3 by determination of enzymatic activity and RT-PCR. The cloned cDNA was expressed in the secretory pathway of the methylotrophic yeast Pichia pastoris and purified after fermentation using a new three-step protocol. mQC converted a set of various substrates with very similar specificity to human QC, indicating a virtually identical catalytic competence. Furthermore, mQC was competitively inhibited by imidazole derivatives. A screen of thiol reagents revealed cysteamine as a competitive inhibitor of mQC bearing a Ki value of 42 +/-2 microM. Substitution of the thiol or the amino group resulted in a drastic loss of inhibitory potency. The pH dependence of catalysis and inhibition support that an uncharged nitrogen of the inhibitors and the substrate is necessary in order to bind to the active site of the enzyme. In contrast to imidazole and cysteamine, the heterocyclic chelators 1,10-phenanthroline, 2,6-dipicolinic acid, and 8-hydroxyquinoline inactivated mQC in a time-dependent manner. In addition, citric acid inactivated the enzyme at pH 5.5. Inhibition by citrate was abolished in the presence of zinc ions. A determination of the metal content by total reflection X-ray fluorescence spectrometry and atomic absorption spectroscopy in mQC revealed stoichiometric amounts of zinc bound to the protein. Metal ion depletion appeared to have no significant effect on protein structure as shown by fluorescence spectroscopy, suggesting a catalytic role of zinc. The results demonstrate that mQC and probably all animal QCs are zinc-dependent catalysts. Apparently, during evolution from an ancestral protease, a switch occurred in the catalytic mechanism which is mainly based on a loss of one metal binding site.

Determination of trace elements in human liver biopsy samples by ICP–MS and TXRF: hepatic steatosis and nickel accumulation

Human liver biopsy samples, collected from 52 individuals, were analysed by inductively coupled plasma-mass spectrometry (ICP-MS) and total reflection X-ray fluorescence (TXRF) spectrometry in a retrospective study (i.e. patient selection and liver biopsy were not for the purpose of element analysis). The freeze-dried samples (typically 0.5-2 mg dry weight) were digested in a laboratory microwave digestion system and solutions with a final volume of 1 mL were prepared. The concentrations of Cr, Mn, Fe, Ni, Cu, Zn, Rb, and Pb were determined by use of a Thermo Elemental X7 ICP-MS spectrometer. TXRF measurements were performed with an Atomika Extra IIA spectrometer. Yttrium was employed as an internal standard, prepared by dissolution of 5N-purity yttria (Y(2)O(3)) in our laboratory. The accuracy was tested by analysis of NIST 1577a Bovine Liver certified reference material. The concentrations of Fe, Cu, Zn, and Rb determined in human liver biopsy samples were in good agreement with data published by other authors. The distribution of nickel in the samples was surprisingly uneven-nickel concentrations ranged from 0.7 to 12 microg g(-1) (dry weight) in 38 samples and in several samples were extremely high, 36-693 microg g(-1). Analysis of replicate procedural blanks and control measurements were performed to prevent misinterpretation of the data. For patients with steatosis (n=14) Ni concentrations were consistently high except for two who had levels close to those measured for the normal group. As far as we are aware no previous literature data are available on the association of steatosis with high concentration of nickel in human liver biopsies taken from living patients.

Multielement Analysis of Soft Drinks by X-ray Fluorescence Spectrometry

Several commercial soft drinks and respective plastic bottles were analyzed for their multielement contents employing the synchrotron radiation total reflection X-ray fluorescence spectrometry technique (SRTXRF). The SRTXRF method has been developed and validated, and about 20 elements were detected in the investigated samples, including some trace elements, which can be toxic for human beings, such as Ti, Cr, Sb, As, and Pb in soft drinks and Al, Sb, As, and Pb in poly(ethylene terephthalate) (PET) containers. Statistical analysis was performed using chemometric techniques (principal component analysis and cluster analysis), and similarities were verified in the multielement contents of the samples. The results demonstrated that the SRTXRF offers a good multielemental approach for the quality control of food products. Moreover, on the basis of enrichment factors, the possibility of the trace elements in the PET container may be leached to the beverages under normal commercial situations and other results were discussed.

Multielement analysis of Nigerian bitumen by TXRF spectrometry and the physical constants characterization of its hydrocarbon component

The Total reflection X-ray fluorescence (TXRF) Spectrometry analytical technique was used for the elemental characterization of bitumen extracted from Nigerian Oil sands. Twelve elements—K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As and Pb were detected and their concentrations, the enrichment factors and correlation determined. Very high enrichment factors were obtained for V, Cr, Ni, Cu, Zn, As and Pb. This has implication for environmental degradation during exploration, refining, transportation and/or marketing of the bitumen. The correlation matrix result indicated that some of the trace elements detected have common sources or similar chemical properties. Samples of the extracted bitumen were also subjected to solvent deasphaltened using n-pentane to obtain maltene and asphaltene. Oil (Hydrocarbon) component was eluted from maltene using n-pentane in a glass chromatographic column, which has been packed with activated neutral alumina of grade Brock Mann 1, type 507 C. The physical characteristics (API gravity, refractive index, viscosity, surface tension and melting point) of the oil eluted from the bitumen were determined. The percentage oil composition (36.98%) was comparable to equivalent values obtained for oil from Athabasca (48.10%) and Venezuela (40.30%) oil sands indicating that Nigerian oil sand is a rich source of petrochemicals. The results of physical characteristics also show that oil could be useful for lubrication purpose.

Direct analysis of Al2O3 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 microg g(-1) as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 microL 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 microm, 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 microg 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.

Parasitic ion-implantation produced by a Kaufman-type ion source used for planar etching of surfaces

Total reflection X-ray fluorescence spectrometry (TXRF) and photoelectron spectroscopy (XPS) were used to characterize ion-etched surfaces of Si wafers, a quartz glass and vacuum-metallized multilayer on a Si wafer. These samples were first treated with low kinetic energy ions of a broad beam Kaufman-type ion source. By repeating this method of sputtering, layers can be removed stepwise and in combination with surface analysis by TXRF a multielement depth profiling can be carried out. The depth resolution is of the order of 3 nm. Unfortunately, ion-etching leads to uncontrollable ion implantation and thus to a contamination of the samples with some 'parasitic' elements which may disturb the multielement characterization of the original surfaces. XPS with Ar sputtering was used to confirm the implantation of interfering elements in the freshly ion-etched samples.

Enhanced gettering of iron impurities in bulk silicon by using external direct current electric field

Iron impurities in bulk silicon are found to getter efficiently at the polysilicon layer by an electric field during isothermal annealing. Experimental results show that iron concentration at the polysilicon layer increases to the level that becomes detectable by total reflection x-ray fluorescence (TXRF) spectroscopy. The improved gettering efficiency for iron is attributed mainly to the directional drift of ionic iron interstitials toward the polysilicon gettering sites, under the influence of the applied potential gradient, thus presenting a more effective method for reducing the iron content in silicon.

Determination of trace elements in uranium oxide by Total Reflection X-ray Fluorescence spectrometry

A study on the applicability of Total Reflection X-ray Fluorescence for the determination of multielements in trace amounts in U 3O 8 matrix has been made. The calibration of the Total Reflection X-ray Fluorescence spectrometer and the validation of the method were done using multielement standards. The trace elements present in U 3O 8 standards and samples were determined after separating the U matrix by solvent extraction using tri- n-butyl phosphate and trioctyl phosphine oxide as extractants. From the aqueous phase the elements K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Pb and Ba, etc., were determined by Total Reflection X-ray Fluorescence using Ga as an internal standard. An intercomparison of the Total Reflection X-ray Fluorescence determined concentrations of the trace elements specific to nuclear fuel, e.g. Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn in U 3O 8 standards/samples with certified concentrations for these elements in U 3O 8 standards and Inductively Coupled Plasma Atomic Emission Spectroscopy determined concentrations in real U 3O 8 samples was also made. The method shows a precision and accuracy better than 5% (1 σ) for most elements in concentration range of ng/mL with a sample size of 10 μL.

Measurement of the silicon dioxide concentration in hafnium silicate gate dielectrics with a total reflection X-ray fluorescence spectroscopy

As complementary metal oxide semiconductor devices continue to scale along the rapid pace of Moore’s law, gate dielectric materials with significantly higher dielectric constant (k=10–25) are being evaluated as replacements for conventional silicon dioxide, SiO2 (k=3.9), and silicon oxynitride. This allows for the introduction of a physically thicker film with lower leakage current and with capacitance equivalent to a thinner (1.0 nm and below) SiO2 layer (Schlom and Haeni, 2002; Wilk et al., 2001; Kingon et al., 2001). Although binary metal oxide films such as HfO2 and ZrO2 exhibit higher permittivity than their corresponding silicates and aluminates, alloyed with various molecular percents of SiO2 or Al2O3, respectively, they are compromised by lower onset of crystallization temperature which contributes a higher degree of interfacial microroughness and increased gate leakage current due to dislocations and oxygen vacancies generated along grain boundaries. Accordingly, development of hafnium silicate has been the subject of intense investigation as an advanced gate dielectric thin film designed to meet the device manufacturing requirements of thermal stability in direct contact with substrate silicon and metal gate electrode materials. In this paper, we present results corresponding to the utilization of total reflection X-ray fluorescence spectroscopy (TXRF) as a quick, accurate, nondestructive technique for hafnium silicate composition determination based on detection of the Hf:Si ratio of (HfO2)x(SiO2)1−x, where x varies over the range 0.2–1.0.

Evaluation of chemometric techniques and artificial neural networks for cancer screening using Cu, Fe, Se and Zn concentrations in blood serum

It is known that variations in the concentrations of certain trace elements in bodily fluids may be an indication of an alteration of the organism's normal functioning. Multivariate analysis of such data, and its comparison against proper reference values, can thus be employed as possible screening tests. Such analysis has usually been conducted by means of chemometric techniques and, to a lower extent, backpropagation artificial neural networks. Despite the excellent classification capacities of the latter, its development can be time-consuming and computer-intensive. Probabilistic artificial neural networks represent another attractive, yet scarcely evaluated classification technique which could be employed for the same purpose. The present work was aimed at comparing the performance of two chemometric techniques (principal component analysis and logistic regression) and two artificial neural networks (a backpropagation and a probabilistic neural network) as screening tools for cancer. The concentrations of copper, iron, selenium and zinc, which are known to play an important role in body chemistry, were used as indicators of physical status. Such elements were determined by total reflection X-ray fluorescence spectrometry in a sample of blood serum taken from individuals who had been given a positive ( N = 27) or a negative ( N = 32) diagnostic on various forms of cancer. The principal components analysis served two purposes: (i) initial screening of the data; and, (ii) reducing the dimension of the data space to be input to the networks. The logistic regression, as well as both artificial neural networks showed an outstanding performance in terms of distinguishing healthy (specificity: 90–100%) or unhealthy individuals (sensitivity: 100%). The probabilistic neural network offered additional advantages when compared to the more popular backpropagation counterpart. Effectively, the former is easier and faster to develop, for a smaller number of variables has to be optimized, and there are no risk of overtraining.

Vapor phase decomposition–droplet collection–total reflection X-ray fluorescence spectrometry for metallic contamination analysis on Ge wafers

Ge substrates are recently being reconsidered as a candidate material for the replacement of Si substrates in advanced semiconductor devices. The reintroduction of this material requires reengineering of the standard IC processing steps. In this paper, we present the extension of the methodology of vapor phase decomposition–droplet collection–total reflection X-ray fluorescence spectrometry (VPD–DC–TXRF) for metallic contamination analysis towards Ge substrates. A first step that asked for adaptation was the collection chemistry as the Ge wafers surface is not hydrophobic after the VPD treatment. The contact angle could be significantly increased using a concentrated HCl solution. This chemistry has been proved to perform well in the collection of metals from intentionally contaminated Ge wafers. A second step that needed optimization was the matrix removal method as a sample preparation step prior to the TXRF analysis. First, the upper limits of TXRF on Ge containing solutions have been characterized. The accuracy of TXRF is found to be acceptable for Ge contents lower than 1×10 14 atoms (250 ppb in 50 μL) but decreases systematically with higher Ge contents. Fortunately, Ge can be volatilized at low temperatures as GeCl 4 by the addition of HCl. The parameters within this method have been investigated with respect to the removal of Ge and the recovery of metal traces. Finally, the full VPD–DC–TXRF method has been applied on intentionally contaminated Ge wafers and proved to be very accurate.

Determination of the Ta and Nb ratio in LiNb 1− xTa xO 3 by total reflection X-ray fluorescence spectrometry

A procedure for evaluation of the mass ratio between Ta and Nb in LiNb 1− x Ta x O 3 single crystals by total reflection X-ray fluorescence spectrometry (TXRF) is described. The developed procedure does not require chemical preparation of the samples and it proves to be fast (30 min for sample preparation and 10 min for analysis), precise (down 1% RSD) and easy to perform. To check the methodology, the lattice parameter of each LiNb 1− x Ta x O 3 sample was determined by powder X-ray diffraction. While the a hexagonal lattice parameter remains constant, a strong and linear dependence of the c hexagonal lattice parameter with Ta content in molar percentage has been observed for the first time.

Determination of catalyst metal residues in polymers by X-ray fluorescence

Commercial polyethylenes produced by Ziegler-Natta, Philips and metallocene technology were analyzed by X-ray fluorescence spectroscopy. Synthetic standards using wax matrix was shown to be suitable for the calibration curve in comparison to those prepared by milling and grinding virgin polymer mixed with standard metal oxide as matrix. The detection limits obtained for the studied metal in the different polymers were: 12 mg kg −1 for Mg, 0.8 mg kg −1 for Ti, 1.6 mg kg −1 for Cr, 1.2 mg kg −1 for Zr and 1.9 mg kg −1 for V. For comparative reasons, the determination of residual metal content by Rutherford backscattering spectrometry (RBS) and total-reflection X-ray fluorescence spectrometry (TXRF) is also discussed.

Characterization of Hypoglycemiant Plants by Total Reflection X-ray Fluorescence Spectrometry

In this work, synchrotron radiation total reflection X-ray fluorescence spectrometry (SRTXRF) was used to determine trace elements in eight hypoglycemiant plants (Trigonella foenum graecum, Panax ginseng, Pfaffia paniculata, Myrcia speciosa, Zea mays, Harpagophytum procumbens, Syzygium jambolona, and Bauhinia forficate). The elements P, K, Ca, Ti, Mn, Fe, Cu, Zn, Rb, and Sr were detected in all medicinal plants investigated, whereas Si, S, Sc, V, Cr, Co, Ni, Se, Nb, Mo, Sn, Sb, Ba, Hg, and Pb were detected only in some of the samples. The concentration of elements in hypoglycemiant plants varied from 0.15 microg/g of Co to 3.0 x 10(4) microg/g of K and the mean of experimental limit of detection for these elements were 0.14 and 3.6 microg/g, respectively.

Multi-element analysis of sea water from Sepetiba Bay, Brazil, by total reflection x-ray fluorescence spectrometry using synchrotron radiation

Trace elements in the surface waters of Sepetiba Bay were studied by total reflection x-ray fluorescence spectrometry using synchrotron radiation (SRTXRF). The bay is located in the south of Rio de Janeiro State, Brazil. The water samples were collected at 21 sampling stations, prepared in order to preconcentrate the metallic elements with ammonium pyrrolidinedithiocarbamate and to remove the salt matrix. Samples were spiked with an internal standard (Se) and the precipitated dithiocarbamates of trace elements were separated by filtration through a Millipore filter, then transferred to a Perspex reflector and digested with HNO3 for SRTXRF measurement. Elemental concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo and Pb were determined and a comparison was made between the results obtained and the values given in the literature for sea water. Copyright © 2005 John Wiley & Sons, Ltd.