Analysis of archaeological ceramics by total-reflection X-ray fluorescence: Quantitative approaches

This paper reports the quantitative methodologies developed for the compositional characterization of archaeological ceramics by total-reflection X-ray fluorescence at two levels. A first quantitative level which comprises an acid leaching procedure, and a second selective level, which seeks to increase the number of detectable elements by eliminating the iron present in the acid leaching procedure. Total-reflection X-ray fluorescence spectrometry has been compared, at a quantitative level, with Instrumental Neutron Activation Analysis in order to test its applicability to the study of this kind of materials. The combination of a solid chemical homogenization procedure previously reported with the quantitative methodologies here presented allows the total-reflection X-ray fluorescence to analyze 29 elements with acceptable analytical recoveries and accuracies.     

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 10³-10⁴. The recommended colonization time for biomonitoring of the Lake Velence is 6 weeks applying polycarbonate substrates.     

Determination of fluorine by total reflection X-ray fluorescence spectrometry

There is a growing interest in determination of low Z elements, i.e. carbon to phosphorus, in various samples. Total reflection X-ray fluorescence spectrometry (TXRF) has been already established as a suitable trace element analytical method with low sample demand and quite good quantification limits. Recently, the determinable element range was extended towards Z = 6 (carbon).     

Application of total-reflection X-ray fluorescence spectrometry in material analysis

X-ray fluorescence spectrometry with total reflection conditions is applied in the qualitative and quantitative determination of impurities in thin layers of Ti, TiO₂, and HfO₂ prepared by evaporation and of SiO₂, TiO₂, and Ta₂O₅ prepared by ion beam sputtering. The same method is used to examine stainless steel discs, which have to be used as reference materials,Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Determination of metal-cofactors in enzyme complexes by total-reflection X-ray fluorescence spectrometry

The determination of metal-cofactors and their molar concentrations is an important requirement for the characterisation of metalloproteins and a challenge regarding the capabilities of trace analytical methods. In this respect, total-reflection X-ray fluorescence spectrometry offers many advantages for the determination of trace elements in enzymes, as compared to other well known analytical techniques such as flame atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry (ICP-AES), because of the significantly smaller amounts of sample required. Without any decomposition, elements like P, S, Fe, Ni, Cu, Zn, Mn and Mo could be determined with high accuracy, in spite of the large bio-organic matrix. The enzymes (polysulphide reductase and hydrogenase of the rumen bacterium Wolinella succinogenes, and the cytochrome c oxidase and quinol oxidase of the soil bacterium Paracoccus denitrificans) were transferred from their usual salt-buffer into a solution of 100 mmol l⁻¹ tris(hydroxymethyl)aminomethane (tris)-acetate containing an appropriate detergent. By this procedure, an improved signal-to-noise ratio is obtained. The polysulphide reductase was found to contain copper as a hitherto existing unknown cofactor. The enzyme contains a stretch of amino acids that are typical of copper proteins and thus confirm the presence of this element. Furthermore, the data concerning cytochrome c oxidase from Paracoccus denitrificans are in good agreement with published values obtained by ICP-AES. Also, results from measurements with the quinol oxidase from the same bacterium agree with the expected values. The investigations lead to the conclusion that the method is well suited to the quantitative determination of metals in enzymes, in particular their molar fractions, and requires only small amounts of the biological sample without any extensive pretreatment. © 1997 Elsevier Science B.V.     

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 μL 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).     

A solid phase extraction procedure for the simultaneous determination of total inorganic arsenic and trace metals in seawater: Sample preparation for total-reflection X-ray fluorescence

In this paper we present a procedure allowing total-reflection X-ray fluorescence spectrometry (TXRF) determinations of arsenic in water samples, especially in seawater samples. The procedure consists of an arsenate reduction step (performed by using a l-cysteine solution) followed by a complexation of As⁺³ with sodium dibenzyldithiocarbamate and solid phase extraction. The new procedure is a modification of a method developed by Prange and allows a simultaneous determination of As together with V, Fe, Ni, Cu, Zn, Pb, and U in seawater by TXRF. The procedure was tested using the Certified Reference Material CASS-4 and was later applied to regular seawater samples collected from the North Sea. The detection limit for arsenic is 10 ng L^− 1.     

Three empirical cases of the deposition morphology influence in the analytical quality of direct solid suspension measurements by total-reflection X-ray fluorescence

This work describes three empirical cases where the influence of the microscopic and macroscopic morphology of the sample depositions analyzed by total-reflection X-ray fluorescence with respect to the accuracy and uncertainties of its analytical results is shown. The first case was the direct solid analysis of reference clay, where a strong dependence between the accuracy and the uncertainty of the evaluated elements with respect to the microscopic morphology of the depositions obtained in water and toluene liquid medium was observed. The second case was the analysis of a solid suspension of magnetite nanoparticles, where the evaluation of the different macroscopic deposition morphologies, for different kinds of sample carriers and evaporation processes, produces an important variation of the uncertainty associated to the Fe measurements but not for its nominal values. Finally, the third case was the analysis of Ru and Se impregnated in carbon nanoparticles. In this case, the ultrasonic modifications of the particle size distributions in the solid suspensions, together with the macroscopic morphology variation of its solid depositions, produce drastic consequences in the uncertainties associated with the metallic content.     

Optimization of the quantitative direct solid total-reflection X-ray fluorescence analysis of glass microspheres functionalized with Zr organometallic compounds

Quantitative determination of Zr in the system constituted by quartz microspheres functionalized with two kinds of organometallic compounds has been studied due to the importance of the correct quantization of the Zr from a catalytic point of view. Two parallel approximations were done, i.e. acid leaching and direct solid quantization. To validate the acid leaching TXRF measures, ICP-MS analysis were carried out. The results obtained by means of the optimization of the quantitative direct solid procedure show that, with a previous particle size distribution modification, TXRF obtain the same analytical results as ICP-MS and TXRF by acid leaching way but without previous chemical acid manipulation. This fact implies an important improvement for the analysis time, reagents costs and analysis facility and it proves again the versatility of TXRF to solve analytical problems in an easy, quick and accurate way. Additionally and for the direct solid TXRF measurements, a deeper study was done to evaluate the intrinsic analytical parameters of the Zr TXRF analysis of this material. So, the influence of the particle size distributions (modified by means of a high power ultrasound probe) with respect to uncertainty and detection limits for Zr were developed. The main analytical conclusion was the strong correlation between the average particle sizes and the TXRF analytical parameters of Zr measurements, i.e. concentration, accuracy, uncertainty and detection limits.     

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.     

Macromolecules by total reflection X-ray fluorescence: marking techniques

This paper proposes an optimized method to mark polysaccharide macromolecules with heavy atoms in order to make possible their detection by total reflection X-ray fluorescence. A chemical reaction was employed to produce the substitution of OH groups of the polymer macromolecules by iodine atoms. Temperature, time, concentration of reactants and pH of the labeling chemical reaction were the variables and the relative sensitivities of the introduced atoms in the TXRF determinations were the optimization parameters for the TXRF determinations. Control of the physical properties of the polymer and the labeled product were made in order to prevent chemical alterations. The quantification of the labeled macromolecules was made by a previous careful calibration.     

Determination of metal-cofactors in respiratory chain complexes by total-reflection X-ray fluorescence spectrometry (TXRF)

Total Reflection X-Ray Fluorescence Spectrometry (TXRF) offers many advantages for the detection of trace elements in enzymes as compared to other well known analytical techniques like flame-AAS or ICP-AES because of the significantly smaller amounts of sample required. Without any decomposition, elements like Fe, Ni, Cu, Zn, Mn and Mo could be determined with high accuracy, in spite of the large bio-organic matrix. Besides the metals also sulfur can be determined in protein samples. The two terminal oxidases, cytochrome c oxidase and quinol oxidase, isolated from the soil bacterium Paracoccus denitrificans, were transferred from their usual salt buffer into a solution of 100 mmol/L tris(hydroxymethyl)aminomethane (TRIS) acetate containing an appropriate detergent. By this procedure an improved signal/noise ratio is attained. The data for cytochrome c oxidase are in good agreement with values obtained by ICP-AES. Further results of quinol oxidase, which has different element ratios, also fit the expected values. The investigations lead to the conclusion that the method is well suited for the quantitative determination of metals in enzymes, and in particular their molar ratios, and requires only small amounts of the biological sample without any extensive pretreatment. Received: 17 June 1997 / Revised: 21 November 1997 / Accepted: 27 November 1997     

Determination of metal-cofactors in respiratory chain complexes by total-reflection X-ray fluorescence spectrometry (TXRF)

Total Reflection X-Ray Fluorescence Spectrometry (TXRF) offers many advantages for the detection of trace elements in enzymes as compared to other well known analytical techniques like flame-AAS or ICP-AES because of the significantly smaller amounts of sample required. Without any decomposition, elements like Fe, Ni, Cu, Zn, Mn and Mo could be determined with high accuracy, in spite of the large bio-organic matrix. Besides the metals also sulfur can be determined in protein samples. The two terminal oxidases, cytochrome c oxidase and quinol oxidase, isolated from the soil bacterium Paracoccus denitrificans, were transferred from their usual salt buffer into a solution of 100 mmol/L tris(hydroxymethyl)aminomethane (TRIS) acetate containing an appropriate detergent. By this procedure an improved signal/noise ratio is attained. The data for cytochrome c oxidase are in good agreement with values obtained by ICP-AES. Further results of quinol oxidase, which has different element ratios, also fit the expected values. The investigations lead to the conclusion that the method is well suited for the quantitative determination of metals in enzymes, and in particular their molar ratios, and requires only small amounts of the biological sample without any extensive pretreatment.     

Study of interaction of iron and lead during their uptake process in wheat roots by total-reflection X-ray fluorescence spectrometry

Microwave assisted acidic digestion and total-reflection X-ray fluorescence spectrometry (TXRF) was used for the determination of lead and iron in wheat roots cultured in CaSO₄ solution, and treated with Pb(NO₃)₂ and Fe(III)–citrate or Fe(III)–EDTA under controlled conditions, respectively. It was established that lead has a stimulation effect on the iron uptake in the presence of Fe(III)–citrate. The lead uptake, however, is hardly influenced by iron independently from the complex forming agents applied. To check the stability of the accumulated iron and lead constituents, some of the roots were washed with various solutions and the removable iron and lead were also measured by TXRF. These experiments indicate that the presence of lead results in higher stability of iron constituents in the root; however, iron does not have any effect on the lead constituents, the stabilities of which increase in the order Pb–citrate<Pb–(cell wall)<Pb–EDTA. © 1997 Elsevier Science B.V.     

Determination of carbon in natural freshwater biofilms with total reflection X-ray fluorescence spectrometry

There is a growing interest in determination of low Z elements, i.e., carbon to phosphorus, in biological samples. Total reflection X-ray fluorescence spectrometry (TXRF) has been already established as suitable trace element analytical method with low sample demand and quite good quantification limits. Recently, the determinable element range was extended towards Z = 6 (carbon).Biofilms can be used for biomonioring purposes in the aquatic environment. Besides the trace metals, especially the determination of the carbon content is important for the better understanding of the early stage of biofilm formation. For this, an ATI low Z spectrometer equipped with Cr-anode X-ray tube, multilayer monochromator, vacuum chamber, and a Si(Li) detector with ultra thin window was used. Biofilms were grown on two different artificial supports (granite and plexiglass), freeze dried, suspended in high purity water and analyzed. As an internal standard the natural titanium content of the biofilms was used. The accuracy of the method was checked by total carbon measurement using a combusting carbon analyzer.     

Size-fractionated sampling and chemical analysis by total-reflection X-ray fluorescence spectrometry of PMx in ambient air and emissions

PM 10 and PM 2.5 (PMx) have been recently introduced as new air quality standards in the EU (Council Directive 1999/30/EC) for particulate matter. Different estimates and measurements showed that the limit values for PM 10 will be exceeded at different locations in Europe, and thus measures will have to be taken to reduce PMx mass concentrations. Source apportionment has to be carried out, demanding comparable methods for ambient air and emission sampling and chemical analysis. Therefore, a special ambient-air sampler and a specially designed emission sampler have been developed. Total-reflection X-ray fluorescence analysis (TXRF) was used for multi-element analyses as a fast method with low detection limits. For ambient air measurements, a sampling unit was built, impacting particle size classes 10–2.5 μm and 2.5–1.0 μm directly onto TXRF sample carriers. An electrostatic precipitator (ESP) was used as back-up filter to also collect particles <1 μm directly onto the TXRF sample carriers. Air quality is affected by natural and anthropogenic sources, and the emissions of particles <10 μm and <2.5 μm, respectively, have to be determined to quantify their contributions to the so-called coarse (10–2.5 μm) and fine (<2.5 μm) particle modes in ambient air. For this, an in-stack particle sampling system was developed, according to the new ambient air quality standards and in view of subsequent analysis by TXRF. These newly developed samplers, in combination with TXRF analyses, were employed in field campaigns to prove the feasibility and capabilities of the approach. Ambient air data show the quantification of a wide spectrum of elements. From those concentrations, PMx ratios were calculated as an indicator for different sources of elements. Results useful for source apportionment are also the elemental day/night ratios calculated to determine local contributions to PMx mass concentrations. With regard to the emission measurements, results of mass and elemental concentrations obtained in two different processes (steel industry) show that the new PM 10/PM 2.5 cascade impactor and measurements with TXRF give characteristic fingerprints for different sources. Size-fractionated ambient air and emission sampling, together with multi-element analysis, prove to be a useful approach to derive information for source–receptor modeling, a method necessary to set up effective abatement strategies to reduce PMx mass concentrations.     

Total reflection X-ray fluorescence analysis of oral fluids of women affected by osteoporosis and osteopenia

Osteoporosis is a disease characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures; the early stage of decreased bone density is called osteopenia. More than 200 million people are affected and about 50% of post-menopausic women are expected to develop the disease. Osteoporosis, osteopenia and periodontal disease have in common several risk factors, being hyperthyroidism and smoking habits the most important ones. There is scarce information in the literature about the association between periodontal disease and osteoporosis and/or osteopenia. Some works suggest that osteoporotic women are susceptible to a higher loss of periodontal insertion, alveolar bones, and teeth.     

The use of Si carriers for aerosol particle collection and subsequent elemental analysis by total-reflection X-ray fluorescence spectrometry

The adoption of polished Si carriers was studied for the sensitive elemental analysis of aerosol particles using total-reflection X-ray fluorescence (TXRF) spectrometry. The surface roughness of the Si carrier measured by atomic force microscopy was found to be smaller than those of glassy carbon and quartz glass carriers, which are commonly used for TXRF analysis. The detection limits of elements for the Si carrier were superior to those for the glassy carbon and the quartz glass carriers, presumably due to its smaller surface roughness. For example, the detection limit of Sr for the Si carrier was 9 pg, which was 100 times and 3 times lower than those for the glassy carbon and the quartz glass carriers, respectively. The Si carriers could be successfully applied to the direct aerosol particle collection by impaction and the subsequent elemental analysis by TXRF. From the results of the elemental analysis of aerosol particles, the variations in the concentrations of K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn Sr and Pb with time could be clarified.     

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.