P. Kregsamer

Analytical possibilities of total reflection X-ray spectrometry (TXRF) for trace selenium determination in soils.

Selenium content of soils is an important issue due to the narrow range between the nutritious requirement and toxic effects upon Se exposure. However, its determination is challenging due to low concentrations within complex matrices that hamper the analysis in most spectroscopic techniques. In this study, we explored the possibilities of several analytical approaches combined with total reflection X-ray (TXRF) spectrometry for soil Se determinations. The direct analysis of a solid suspension using 20 mg of fine ground material (<50 μm) has a relatively high Se limit of detection (LOD) of 1 mg/kg (worldwide Se average in soils = 0.4 mg/kg) and is therefore only suitable for seleniferous soils. Several fast and simple analytical strategies were developed to decrease matrix effects and improve the LOD for Se determination in soil digests. On one hand, the application of a liquid-liquid extraction procedure using ethyl ether and the introduction of a Cr absorbent in the instrument configuration were carried out to avoid the associated problems on TXRF analysis of soil extracts due to the high Fe concentrations (∼700 mg/L). On the other hand, a dispersive liquid-liquid microextraction procedure (DLLME) before the TXRF analysis of the soil digest was also developed. The effects of various experimental parameters such as sample volume, effect of major elements present in the soil matrix (Fe), and Se concentration in the sample were investigated. The LOD using this analytical methodology (0.05 mg/kg of Se) was comparable to or lower than those obtained in previous works using other popular spectrometric techniques such as GFAAS, ICPMS, and AFS. The calculated Se concentration for JSAC-0411 ([Se] = 1.32 ± 0.27 mg/kg) using the combination of DLLME and TXRF ([Se] = 1.40 ± 0.23 mg/kg) was in agreement with the certified value.

Total reflection X-ray fluorescence analysis with polarized X-rays, a compact attachment unit, and high energy X-rays

Abstract Excitation of samples in total reflection geometry using energy-dispersive spectrometer systems (TXRF) for the detection of characteristic X-rays has shown to be a very efficient technique. Limits of detection (LD) at the ng ml or pg-level, in absolute mass, are attainable. Three approaches are presented: the use of linearly polarized X-rays after Bragg reflection through 90° as excitation source for total reflection, a stable easily mountable TXRF unit for standard laboratory equipment, and the development of a TXRF experiment for high-energy primary radiation up to 100 keV for the excitation of the K-series of high Z elements, for which preliminary results are given.

Low Z total reflection X-ray fluorescence analysis — challenges and answers ☆

Low Z elements, like C, O, ... Al are difficult to measure, due to the lack of suitable low-energy photons for efficient excitation using standard X-ray tubes, as well as difficult to detect with an energy dispersive detector, if the entrance window is not thin enough. Special excitation sources and special energy dispersive detectors are required to increase the sensitivity and to increase the detected fluorescence signal and so to improve the detection limits. Synchrotron radiation, due to its features like high intensity and wide spectral range covering also the low-energy region, is the ideal source for TXRF, especially of low-Z elements. Experiments at a specific beamline (BL 3-4) at SSRL, Stanford, designed for the exclusive use of low-energy photons has been used as an excitation source. Detection limits <100 fg for Al, Mg and Na have been achieved using quasimonochromatic radiation of 1.7 keV. A Ge(HP) detector with an ultra-thin NORWAR entrance window is used. One application is the determination of low-Z surface contamination on Si-wafers. Sodium, as well as Al, are elements of interest for the semiconductor industry, both influencing the yield of ICs negatively. A detection capacity of 1010 atoms/cm2 is required which can be reached using synchrotron radiation as excitation source. Another promising application is the determination of low-Z atoms implanted in Si wafers. Sodium, Mg and Al were implanted in Si-wafers at various depths. From measuring the dependence of the fluorescence signal on the glancing angle, characteristic shapes corresponding to the depth profile and the relevant implantation depth are found. Calculations are compared with measurements. Finally, aerosols sampled on polycarbonate plates in a Battelle impactor were analyzed with LZ-TXRF using multilayer monochromatized Cr-Kα radiation from a 1300-W fine-focus tube for excitation. Results are presented.

Analytical approaches for Hg determination in wastewater samples by means of total reflection X-ray fluorescence spectrometry

At present, there is a considerable interest in Hg monitoring in wastewater samples due to its widespread occurrence and the high toxicity of most of its compounds. Hg determination in water samples by means of total reflection X-ray fluorescence spectrometry (TXRF) entails some difficulties due to the high vapor pressure and low boiling point of this element that produce evaporation and loss of Hg from the surface of the reflector during the drying process, commonly used for sample preparation in TXRF analysis. The main goal of the present research was to develop a fast and simple chemical strategy to avoid Hg volatilization during the analysis of wastewater samples by TXRF spectrometry. Three different analytical procedures were tested for this purpose: (i) increasing the viscosity of the wastewater sample by adding a non-ionic surfactant (Triton X-114), (ii) Hg immobilization on the quartz reflectors using the extractant tri-isobutylphosphine (Cyanex 471X) and (iii) formation of a stable and non-volatile Hg complex into the wastewater sample. The best analytical strategy was found to be the formation of a Hg complex with thiourea (pH=10) before the deposition of 10 microL of sample on the reflector for following TXRF analysis. Analytical figures of merit such as linearity, limits of detection, accuracy and precision were carefully evaluated. Finally, the developed methodology was applied for the determination of Hg in different types of wastewater samples (industrial effluents, municipal effluents from conventional systems and municipal effluents from constructed wetlands).

Total-reflection X-ray fluorescence analysis using special X-ray sources

Abstract The parameter variations of exciting radiation, like spectral distribution, intensity, brilliance, polarization and the phenomenon of X-ray total reflection, leads to improved lower limits of detection (LLD) in XRF. Observations and results from experiments performed with different X-ray tubes such as fine focus Cu and Mo anodes, a specially designed Au anode operated with 100 kV and high power rotating anodes are reported. Results from measurements with monochromatic X-rays tuned with a multilayer structure as well as the use of polarized X-rays from the synchrotron will be shown. All developed measuring devices will be described in terms of their recent design features showing the possible geometric arrangements denned by the beam-reflector-detector position. The extrapolated detection limits for the K -shell excitation of rare earth elements are in the region of 0.3 ng, for medium Z elements in the pg range and for optimized conditions, with a rotating Cu anode, 170 fg for Mn are achieved corresponding to the pg g −1 (ppt) concentration level.

Aerosol particle chemical characteristics measured from aircraft in the lower troposphere during ACE-2

During the Aerosol Characterization Experiment (ACE-2), filter samples were collected aboard the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Pelican aircraft near Tenerife in June and July of 1997. The flights included constant altitude measurements in the boundary layer as well as profiles up to 3800 m providing detailed chemical information about the composition of the aerosol distribution in the lower troposphere. Three cases with different air mass origins—clean marine air, anthropogenically-influenced air from the European continent, and dust-laden air from the Sahara—were identified. The samples were analyzed by ion chromatography (IC) for ionic species, by combined thermal and optical analysis (TOA) for organic carbon, and by total reflection X-ray fluorescence (TXRF) for elemental composition. Particle composition and size distributions for the range of air masses encountered illustrate links in the chemical and microphysical characteristics of aerosol from different sources. Clean marine air masses were characterized by low particle number and mass concentrations with no detectable metals, while anthropogenically-influenced and dust-laden air had high number, mass, and trace metal concentrations. Anthropogenic sources were characterized by high concentrations of submicron particles and some Fe and Cu, whereas dust particle loadings included a significant mass of micron-sized particles and significant loadings of Fe, in addition to small amounts of Mn, Cu, and Ni. These results showed similar tracers for air mass origin as those found in other measurements of oceanic and continental air masses. Aerosol optical properties were estimated with a simplified model of the aerosol based on the measured compositions. The real and imaginary refractive indices and single scattering albedos differed significantly among the three types of aerosol measured, with clean marine aerosol properties showing the least absorption and dust-containing aerosols showing the most. There were only small differences in optical properties for the two different cases of clean marine aerosol, but some significant differences between the two dust cases. Since measurement uncertainties affect these calculations, we studied the type of mixing and the fraction of absorbing species and found the calculation was sensitive to these variations only for the dust-containing aerosol case, probably due to the small amount of water present. While the optical properties varied little with composition for clean marine and anthropogenically-influenced cases, they showed a strong dependence on variations in particle composition and mixing state for the dust-containing cases.

X-ray fluorescence spectrometry

This annual review of X-ray fluorescence covers developments over the period 1999–2000 in instrumentation and detectors, matrix correction and spectrum analysis software, X-ray optics and microfluorescence, synchrotron XRF, TXRF, portable XRF and on-line applications as assessed from the published literature. The review also includes a survey of applications, covering sample preparation, geological, environmental, archaeological, forensic, biological, clinical, thin films, chemical state and speciation studies. During the current review period, further advances have taken place in the development of high resolution semiconductor detectors and in the design and application of XRF instrumentation for space and planetary research. Overall, the papers reviewed here again confirm the important contribution the XRF technique makes to a wide range of scientific endeavour.

Microanalytical method development for Fe, Cu and Zn determination in colorectal cancer cells

Microanalytical methods suitable for the determination of Fe, Cu in HT-29 (human colon adenocarcinoma) cells treated with different iron compounds (Fe(II) sulfate, Fe(III) chloride, Fe(III) citrate and Fe(III) transferrin) and cultured in medium supplemented or not with 10% (v/v) fetal calf serum (FCS) by total reflection X-ray fluorescence spectrometry (TXRF) and simultaneous graphite furnace atomic absorption spectrometry (GF-AAS) were developed. The developed TXRF method was also suitable for Zn determination in the samples. The main advantage of the proposed methods is the execution of all sample preparation steps following incubation and prior to the elemental analysis in the same Eppendorf tubes. Sample preparation was performed at microscale (115 μL sample volume) with 65% nitric acid and 30% hydrogen peroxide. According to scanning electron microscopic measurements, the organic matrix of the cell samples could be eliminated to the extent that accurate results were obtained for Cu and Fe by analyzing the same samples by TXRF and GF-AAS. Concerning the iron uptake, HT-29 cells incubated in FCS-free medium contained Fe in cca. 5-50 times higher amounts compared to cells cultured in FCS supplemented medium. Pronounced differences in the iron uptake compared to the iron supply (inorganic vs. organic chelated as well as iron(II) vs. iron(III)) were observed in the case of cell lines incubated in FCS-free medium.

Investigation of element distribution and homogeneity of TXRF samples using SR-micro-XRF to validate the use of an internal standard and improve external standard quantification

AbstractTotal reflection X-ray fluorescence analysis (TXRF) offers a nondestructive qualitative and quantitative analysis of trace elements. Due to its outstanding properties TXRF is widely used in the semiconductor industry for the analysis of silicon wafer surfaces and in the chemical analysis of liquid samples. Two problems occur in quantification: the large statistical uncertainty in wafer surface analysis and the validity of using an internal standard in chemical analysis. In general TXRF is known to allow for linear calibration. For small sample amounts (low nanogram (ng) region) the thin film approximation is valid neglecting absorption effects of the exciting and the detected radiation. For higher total amounts of samples deviations from the linear relation between fluorescence intensity and sample amount can be observed. This could be caused by the sample itself because inhomogeneities and different sample shapes can lead to differences of the emitted fluorescence intensities and high statistical errors. The aim of the study was to investigate the elemental distribution inside a sample. Single and multi-element samples were investigated with Synchrotron-radiation-induced micro X-ray Fluorescence Analysis (SR-μ-XRF) and with an optical microscope. It could be proven that the microscope images are all based on the investigated elements. This allows the determination of the sample shape and potential inhomogeneities using only light microscope images. For the multi-element samples, it was furthermore shown that the elemental distribution inside the samples is homogeneous. This justifies internal standard quantification. FigureMicroscope (left) and SR-μ-XRF images (right) of a multi-element sample (V, Mn, Ni, Ge; 10 ng each)

Fundamentals of total reflection X-ray fluorescence

Abstract In the last years, total reflection X-ray fluorescence (TXRF) has shown to be an analytical technique for trace-element analysis. Theoretical considerations for the angular behaviour of scattered and fluorescence intensities are reviewed for the reflector material quartz and Mo-Kα excitation. The main influencing parameters are the critical angle, the transmission coefficient and the angle of refraction. Also the interference effect between incoming and reflected beam (standing wave) for total reflection is described.