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.     

An electrochemical enrichment procedure for the determination of heavy metals by total-reflection X-ray fluorescence spectroscopy

An electrolytic separation and enrichment technique was developed for the determination of trace elements by total-reflection X-ray fluorescence spectroscopy (TXRF). The elements of interest are electrodeposited out of the sample solution onto a solid, polished disc of pure niobium which is used as sample carrier for the TXRF measurement. The electrochemical deposition leads to a high enrichment of the analytes and at the same time to a removal of the matrix. This results in substantially improved detection limits in the lower picogram per gram region. The deposited elements are directly measured by TXRF without any further sample preparation step. The homogeneous thin layer of the analytes is an ideal sample form for TXRF, because scattered radiation from the sample itself is minimized. The proposed sample preparation method is useful particularly for the analysis of heavy metals in liquid samples with for TXRF disturbing matrices, e.g. sea water.     

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.     

Study on Slurry Sampling Technique for the Determination of Trace Metals in Food by Electrothermal Atomic Absorption Spectrometry

The slurry sample introduction approach is a convenient method of solid sampling that allows the rapid and accurate determination of trace metals in foodstuffs by ETAAS. Since complex dissolution of the samples is avoided,sample handling is minimal and possible sources of contamination are reduced. Among which, preparation of suspension and optimization of the graphite furnace heating program are important. First, the samples are pulverized using homogenizer at speed lOOOOr/min. Ninety percent of the particles are less than 30um in diameter after a pulverizing period of 6min for vegetable, fruit and liver; 25min for beef and pork; 8min for cereals, which allow the preparation of stable slurries up to at least 10%. Second, suspensions are prepared in medium containing 0.15% agar as stabilizing agent, which stabilizing time is up to two days.     

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     

Total reflection X-ray fluorescence analysis of pollen as an indicator for atmospheric pollution

The viability of pollen is affected by environmental pollution and its use as a bio-indicator is proposed. Such effects can be observed and quantified by biological tests. However, a more accurate identification of the agents affecting the viability is required in order to validate the biological assay for environmental monitoring. The chemical analysis of pollen is meant to ascertain the existence of a correlation between its reduced biological functions and the presence of pollutants. Moreover, such biological systems act as accumulators and allow the detection and quantification of species present in the environment at low concentrations. Total reflection X-ray fluorescence analysis (TXRF) has been chosen for the investigation due to its high sensitivity, multielement capability and wide dynamic range. Corylus avellana L. (hazel) pollen has been collected in areas with different anthropic impact in the province of Trento, Italy. For the TXRF measurements, a liquid sample is needed, especially if a quantitative analysis is required. In the present work, the analysis after a microwave digestion has been compared with the analysis of a suspension of the pollen samples. In both cases, an internal standard has been used for the quantification. The concentrations of 17 elements ranging from Al to Pb have been determined in 13 samples. Analysis of the suspensions showed to be comparable to that of digested samples in terms of spectral quality, but the latter preparation method gave better reproducibility. Sub-ppm lowest limits of detection were obtained for iron and heavier elements detected.     

Calibration of reference materials for total-reflection X-ray fluorescence analysis by heavy ion backscattering spectrometry

Total-reflection X-ray fluorescence (TXRF) is widely used for the control of metallic contamination caused by surface preparation processes and silicon materials. At least three companies supply a variety of TXRF systems to the silicon integrated circuit (IC) community, and local calibration of these systems is required for their day to day operation. Differences in local calibration methods have become an issue in the exchange of information between IC manufacturers' different FABs (Fabrication Facility) and also between silicon suppliers and IC FABs. The question arises whether a universal set of fluorescence yield curves can be used by these different systems to scale system sensitivity from a single element calibration for calculation of elemental concentrations. This is emphasized by the variety of experimental conditions that are reported for TXRF data (e.g. different angles of incidence for the same X-ray source, different X-ray sources, etc.). It appears that an instrumental factor is required. We believe that heavy ion backscattering spectrometry (HIBS) provides a fundamental method of calibrating TXRF reference materials, and can be used in calculating this instrumental factor. In this paper we briefly describe the HIBS system at the Sandia National Laboratories HIBS User Facility and its application to the calibration of TXRF reference materials. We will compare HIBS and TXRF mapping capabilities and discuss the issues associated with the restrictions of some older TXRF sample stages. We will also discuss Motorola's cross-calibration of several TXRF systems using different elements as references.     

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

Total 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.     

Optimized sample preparation procedures for the analysis of solid materials by total-reflection XRF

The total reflection X-ray fluorescence (TXRF) method has been used for the analysis of various types of solid materials of biological, geological and environmental origin. The sample preparation step prior to TXRF measurements has been optimized for the various solid samples, including their decomposition by applying both a microwave oven and a PTFE bomb. Complete procedures for the optimized decomposition from the point of view of speed and completeness of digestion, as well as of the overall precision and accuracy are presented.     

Optimization of TXRF measurements by variable incident angles

Variable incident angles in TXRF instrumentation open up new possibilities in the field of analytical quality assurance of TXRF measurements as well as the possibility of optimizing the measurement angle with respect to the sample carrier. Measurements on the same sample with different incident angles allow a check to be made on the behavior of the internal standard and the elements under investigation within the sample, which makes quantification more reliable, even for difficult samples. This is demonstrated on the example of standard reference material NIST 1633a comparing the relative fluorescence intensities of the elements K, Ti and Fe obtained from a sample prepared from a suspension and a digestion of the SRM material, respectively. Furthermore, it will be shown how the measurement conditions for different sample carrier materials such as quartz and acrylic glass can be optimized by measuring angular-dependent signal and background intensities.     

Sonication effect on cellular material in sedimentation and gravitational field flow fractionation

Sonication procedures are generally used prior to field flow fractionation (FFF) separation in order to produce suspensions without aggregates. Yeast cells manufactured in active dry wine yeast (ADWY) were placed in an ultrasound water bath in order to disrupt possible clumps and to obtain a single-cell suspension to be used in optimal conditions during fermentation processes. In order to determine whether this sample preparation procedure meets absolute needs, different yeast samples before and after sonication were analysed by two field flow fractionation techniques. It is shown that 2 min of sonication in the sample preparation process is sufficient to obtain an optimal dispersion of the yeast cells, that is, without critical percentage of aggregates. To demonstrate this effect, photographs of the yeast cell suspensions were performed with non-sonicated and sonicated yeast sample dispersion. The resulting data are compared with the elution profiles obtained from the two different FFF techniques. It is demonstrated that fractogram profiles prove the effectiveness of sonication methodologies.     

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.     

Sample pretreatment strategies for total reflection X-ray fluorescence analysis: A tutorial review

In the last years, there has been a revival of total reflection X-ray fluorescence spectrometry (TXRF), which was firstly applied for analytical purposes in the late 80s. The aim of this work is to discuss and compare the current approaches for sample pretreatment including in situ microdigestion, slurry preparation, acid digestion, extraction, etc. prior to TXRF analysis. Advantages and drawbacks inherent to each of those procedures are considered. A comprehensive revision in the period January 2008–July 2013 about different sample preparation strategies prior to TXRF analysis apart from early pioneering reports dealing with sample pretreatment are included in the review. Non-conventional sample pretreatment approaches such as microflow online preconcentration, lab-on-a-chip, etc., are also discussed.Finally, future prospects in sample preparation prior to TXRF analysis are outlined.     

TXRF法测定松花粉中的9种生命元素

建立了微波消解前处理,全反射X射线荧光法(TXRF)同时测定松花粉中K、Ca、Ti、Mn、Fe、Ni、Cu、Zn和Rb9种生命元素含量的分析方法.松花粉原料经过微波消解前处理后,采用全反射X射线荧光光谱净计数、QXAS分析软件解谱和单一内标法进行定量分析.比较了干灰化法、湿消解法和微波消解法3种前处理方法的效果,并确立微波消解法作为样品前处理方法.用微波消解- TXRF法测定了花粉标准物质中的上述9种元素,并计算得到其仪器检出限(LLD)为0.002～0.054 mg/L,方法检出限(LDM)为0.004～0.122 mg/kg.TXRF法测定各元素的相对标准偏差(RSDs)为1.0％～5.5％.该方法操作简单、样品用量少、检出限低,对实际样品松花粉的测定结果与ICP - MS法无显著性差异.     

Applicability of direct total reflection X-ray fluorescence analysis in the case of human blood serum samples

Total Reflection X-Ray Fluorescence (TXRF) is a well-established method, mainly applied in the analysis of liquid samples, offering very low detection limits in most of the cases. Direct application of the TXRF method is not so efficient in blood serum analysis, since the high content of the organic matrix increases significantly the background due to Compton scattering. Chemical treatment of the blood serum samples and related preconcentration techniques have been suggested in the literature, but they are time consuming and increase the possibility of adding contaminants in the sample. In this paper, the applicability of direct TXRF analysis in blood serum samples is examined. The insertion of a Mo filter, after the cut-off reflector, has been found to improve significantly the peak-to-background ratio, especially for the elements of interest such as Cu, Zn, Se and Br. The influence of self-absorption phenomena in the quantification procedure was also investigated with respect to the internal standard used and the sample mass analyzed. Precision and accuracy in the analysis was found to be approximately 4% over the whole atomic number range.     

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)

     

Application of X-ray fluorescence analytical techniques in phytoremediation and plant biology studies

Phytoremediation is an emerging technology that employs the use of higher plants for the clean-up of contaminated environments. Progress in the field is however handicapped by limited knowledge of the biological processes involved in plant metal uptake, translocation, tolerance and plant–microbe–soil interactions; therefore a better understanding of the basic biological mechanisms involved in plant/microbe/soil/contaminant interactions would allow further optimization of phytoremediation technologies. In view of the needs of global environmental protection, it is important that in phytoremediation and plant biology studies the analytical procedures for elemental determination in plant tissues and soil should be fast and cheap, with simple sample preparation, and of adequate accuracy and reproducibility. The aim of this study was therefore to present the main characteristics, sample preparation protocols and applications of X-ray fluorescence-based analytical techniques (energy dispersive X-ray fluorescence spectrometry—EDXRF, total reflection X-ray fluorescence spectrometry—TXRF and micro-proton induced X-ray emission—micro-PIXE). Element concentrations in plant leaves from metal polluted and non-polluted sites, as well as standard reference materials, were analyzed by the mentioned techniques, and additionally by instrumental neutron activation analysis (INAA) and atomic absorption spectrometry (AAS). The results were compared and critically evaluated in order to assess the performance and capability of X-ray fluorescence-based techniques in phytoremediation and plant biology studies. It is the EDXRF, which is recommended as suitable to be used in the analyses of a large number of samples, because it is multi-elemental, requires only simple preparation of sample material, and it is analytically comparable to the most frequently used instrumental chemical techniques. The TXRF is compatible to FAAS in sample preparation, but relative to AAS it is fast, sensitive and multi-elemental. The micro-PIXE technique requires rather expensive instrumentation, but offers multi-elemental analysis on the tissue and cellular level.     

Determination of calcium, potassium, manganese, iron, copper and zinc levels in representative samples of two onion cultivars using total reflection X-ray fluorescence and ultrasound extraction procedure

The chemical characterization of onion cultivar samples is an important tool for the enhancement of their productivity due to the fact that chemical composition is closed related to the quality of the products. A new sample preparation procedure for elemental characterization is proposed, involving the acid extraction of the analytes from crude samples by means of an ultrasonic bath, avoiding the required digestion of samples in vegetable tissue analysis. The technique of total reflection X-ray fluorescence (TXRF) was successfully applied for the simultaneous determination of the elements Ca, K, Mn, Fe, Cu and Zn. The procedure was compared with the wet ashing and dry ashing procedures for all the elements using multivariate analysis and the Scheffé test. The technique of flame atomic absorption spectrometry (FAAS) was employed for comparison purposes and accuracy evaluation of the proposed analysis method. A good agreement between the two techniques was found when using the dry ashing and ultrasound leaching procedures. The levels of each element found for representative samples of two onion cultivars (Yellow Granex PRR 502 and 438 Granex) were also compared by the same method. Levels of K, Mn and Zn were significantly higher in the 438 Granex cultivar, while levels of Ca, Fe and Cu were significantly higher in the Yellow Granex PRR 502 cultivar.     

The potential of asymmetric flow field-flow fractionation hyphenated to multiple detectors for the quantification and size estimation of silica nanoparticles in a food matrix

This work represents a first systematic approach to the size-based elemental quantification and size estimation of metal(loid) oxide nanoparticles such as silica (SiO₂) in a real food matrix using asymmetric flow field-flow fractionation coupled online with inductively coupled plasma mass spectrometry (ICP-MS) and multi-angle light scattering (MALS) and offline with transmission electron microscopy (TEM) with energy-dispersive X-ray analysis (EDAX). Coffee creamer was selected as the model sample since it is known to contain silica as well as metal oxides such as titania at the milligramme per kilogramme levels. Optimisation of sample preparation conditions such as matrix-to-solvent ratio, defatting with organic solvents and sonication time that may affect nanoparticle size and size distribution in suspensions was investigated. Special attention was paid to the selection of conditions that minimise particle transformation during sample preparation and analysis. The coffee creamer matrix components were found to stabilise food grade SiO₂ particles in comparison with water suspensions whilst no significant effect of defatting using hexane was found. The use of sample preparation procedures that mimic food cooking in real life was also investigated regarding their effect on particle size and particle size distribution of silica nanoparticles in the investigated food matrix; no significant effect of the water temperature ranging from ambient temperature to 60 °C was observed. Field-flow fractionation coupled to inductively coupled plasma-mass spectrometry (FFF-ICP-MS) analysis of extracts of both unspiked coffee creamer and coffee creamer spiked with food grade silicon dioxide, using different approaches for size estimation, enabled determination of SiO₂ size-based speciation. Element-specific detection by ICP-MS and post-FFF calibration with elemental calibration standards was used to determine the elemental composition of size fractions separated online by FFF. Quantitative data on mass balance is provided for the size-based speciation of the investigated inorganic nano-objects in the complex matrix. The combination of FFF with offline fractionation by filtration and with detection by ICP-MS and TEM/EDAX has been proven essential to provide reliable information of nanoparticle size in the complex food matrix.

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.