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.     

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).     

Investigation of polyelectrolytes by total reflection X-ray fluorescence spectrometry

Water soluble polyelectrolyte samples containing mono-, bi- and trivalent metal ions were investigated without any pretreatment. Acid digestion of linear polymers may lead to a product insoluble in water so the digestion has to be avoided. The determination of analytical characteristics and limitations of the total reflection X-ray fluorescence (TXRF) analysis for poly(vinylalcohol-vinylsulfate) copolymers containing the following cations: Cs⁺; Ba²⁺; Cu²⁺ and La³⁺ are presented in this communication. On the basis of our results efficiency of ion-exchange during preparation of polyelectrolytes and stoichiometry of the end-product were determined. TXRF results were compared with data gained by inductively coupled plasma atomic emission spectrometry (ICP-AES) measurements except in the case of Cs⁺, which has poor sensitivity in ICP-AES. Good agreement was found between the results of the two techniques and calculations from titrimetric data. Concentration of Li⁺ and Mg²⁺ in polymer samples was measured only by ICP-AES.     

Determination of Zn/Cu ratio and oligoelements in serum samples by total reflection X-ray fluorescence spectrometry for cancer diagnosis

The method of quantification using the Compton peak as an internal standard, developed in a previous work, was applied to the routine determination of Fe, Cu, Zn and Se in serum samples from normal individuals and cancer patients by total reflection X-ray fluorescence spectrometry. Samples were classified according to age and sex of the donor, in order to determine reference values for normal individuals. Results indicate that the Zn/Cu ratio and the Cu concentration could prove to be useful tools for cancer diagnosis. Significant differences in these parameters between the normal and cancer group were found for all age ranges. The multielemental character of the technique, coupled with the small amounts of sample required and the short analysis time make it a valuable tool in clinical analysis.     

Characterization of nuclear materials by total reflection X-ray fluorescence spectrometry

Nuclear energy is one of the available energy options for long term energy security of world. In order to produce electricity using this mode of energy generation in an efficient and safe manner, it is necessary that the materials used for such energy generation comply with the specifications assigned. The major and trace composition of these materials is an important specification for their quality control. Different analytical techniques are used for such quality control. Total reflection X-ray fluorescence (TXRF) is a comparatively new technique having several features well suited for trace and major element determinations in nuclear materials. However, this technique has not been used so far extensively for characterization of nuclear materials. The present paper gives a brief introduction of TXRF, its suitability for nuclear material characterization and some details of the TXRF studies made in our laboratory for the characterization of nuclear materials.     

Uranium determination in seawater by total reflection X-ray fluorescence spectrometry

A study regarding uranium determination in seawater by total reflection X-ray fluorescence (TXRF) spectrometry is reported. Uranium, present in seawater in concentration of about 3.3 ng/mL, was selectively extracted in diethyl ether and determined by TXRF after its preconcentration by evaporation and subsequent dissolution in a small volume of 1.5% suprapure HNO₃. Yttrium was used as an internal standard. Before using diethyl ether for selective extraction of uranium from seawater, its extraction behavior for different elements was studied using a multielement standard solution having elemental concentrations in 5 ng/mL levels. It was observed that the extraction efficiency of diethyl ether for uranium was about 100% whereas for other elements it was negligible. The detection limit of TXRF method for uranium in seawater samples after pre-concentration step approaches to 67 pg/mL. The concentrations of uranium in seawater samples determined by TXRF are in good agreement with the values reported in the literature. The method shows a precision within 5% (1σ). The study reveals that TXRF can be used as a fast analytical technique for the determination of uranium in seawater.     

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).     

Simultaneous determination of elemental content in water samples by total reflection X-ray fluorescence and atomic absorption spectrometry

An analytical exercise between two laboratories was performed in order to compare the elemental composition of a water sample. The metal concentration of Cr, Cu, Fe, Mn, Ni, Pb, and Zn in the water sample was analyzed by Total Reflection X-Ray Fluorescence and Atomic Absorption Spectrometry. The analysis by Total Reflection X-Ray Spectrometry was realized by an Ital Structures TX-2000 and the analysis by Atomic Absorption Spectrometry was made by a Perkin Elmer Spectrophotometer Model 3110. Results show a good agreement in the metal concentrations obtained by both techniques. The variation coefficient between the results with both techniques was less than 14%. Therefore, it is possible to conclude that both techniques are reliable and adequate for the determination of these elements in environmental water samples.     

Analysis of nutrition-relevant trace elements in human blood and serum by means of total reflection X-ray fluorescence (TXRF) spectroscopy

In clinical service laboratories, one of the most common analytical tasks with regard to inorganic traces is the determination of the nutrition-relevant elements Fe, Cu, Zn, and Se.     

Trace analysis of high-purity iron by total reflection X-ray fluorescence spectrometry

Summary A combined procedure enabling simultaneous multielement analysis of trace impurities in high-purity iron is presented. After removal of the iron matrix by solvent extraction with methyl isobutyl ketone, the trace elements Ti, V, Cr, Mn, Ni, Cu, Pb and Bi are determined by means of total reflection X-ray fluorescence analysis. Detection limits are found in the range of 100 ng/g. The reliability of the method is verified by the analysis of commercial high-purity iron and by the comparison of analytical data obtained by ICP-AES.     

Trace analysis of high-purity copper by total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence (TXRF) analysis after the separation of matrix element was studied for the determination of trace impurity elements (Ca, Sc, V, Cr, Mn, Fe, Co, Ni and Zn) in high purity copper. Matrix copper was removed by electrolysis (0.2 A, 8 h) of a nitric acid solution. A 10 μL aliquot of the remaining solution of the electrolysis was dropped on a silicon-wafer sample-carrier and dried in a vacuum. This was repeated five times and the precipitate of five 10 μL-aliquots was analyzed by TXRF using a W-Lβ beam with an incident angle of 0.05?°. TXRF analytical values were obtained by using relative sensitivity factors of the analytes to the internal standard element (Pd). Detection limits of the analytes ranges from 0.077 ng for Zn to 0.785 ng for Ca.     

Trace analysis of high-purity copper by total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence (TXRF) analysis after the separation of matrix element was studied for the determination of trace impurity elements (Ca, Sc, V, Cr, Mn, Fe, Co, Ni and Zn) in high purity copper. Matrix copper was removed by electrolysis (0.2 A, 8 h) of a nitric acid solution. A 10 μL aliquot of the remaining solution of the electrolysis was dropped on a silicon-wafer sample-carrier and dried in a vacuum. This was repeated five times and the precipitate of five 10 μL-aliquots was analyzed by TXRF using a W-Lβ beam with an incident angle of 0.05 °. TXRF analytical values were obtained by using relative sensitivity factors of the analytes to the internal standard element (Pd). Detection limits of the analytes ranges from 0.077 ng for Zn to 0.785 ng for Ca. Received: 25 December 1997 / Revised: 30 March 1998 / Accepted: 2 April 1998     

Application of total reflection X-ray fluorescence spectrometry for multi-elements characterization in human hair

Biomonitoring of Cr, Fe, Ni, Cu, Zn and Pb in scalp hair of the rural population in Punjab state of India was carried out using TXRF. The objective of the study was to understand their exposure to the trace elements from the local environment. The volunteers having age group 30–45 years were selected from rural region of Punjab. Validity of method was checked by analyzing Certified Reference Materials IAEA-436 and INCT-MPH-2. The results of trace elements analysis in hair samples shows no environmental gradient in the concentration of the elements like Cr, Fe, Ni, Cu, Zn however Pb was observed higher in few volunteers as compared to published value of concentrations in volunteers from Delhi.     

Determination of sulphur in uranium matrix by total reflection X-ray fluorescence spectrometry

The possibility of sulphur determination in uranium matrix by total reflection x-ray fluorescence spectrometry (TXRF) has been studied. Calibration solutions and samples of sulphur in uranium matrix were prepared by mixing uranium in form of a standard uranyl nitrate solution and sulphur in the form of Na₂SO₄ standard solution, prepared by dissolving Na₂SO₄ in Milli-Q water. For major element analysis of sulphur, it was determined without separation of uranium whereas for the trace level determinations, uranium was first separated by solvent extraction using 30% tri-n-butyl phosphate (TBP) in dodecane as an extractant. In order to countercheck the TXRF results, a few samples of Rb₂U(SO₄)₃, a chemical assay standard for uranium, were diluted to different dilutions and sulphur content in these solutions were determined. The TXRF determined results for trace determinations of sulphur in these diluted solutions were counterchecked after addition of another uranium solution, so that sulphur is at trace level compared to uranium, separating uranium from these solution mixtures using TBP extraction and determining sulphur in aqueous phase by TXRF. For such TXRF determinations, Co was used as internal standard and W Lα was used as excitation source. The precision and accuracy of the method was assessed for trace and major element determinations and was found to be better than 8% (1σ RSD) and 15% at a concentration level of 1 μg/mL of sulphur measured in solutions whereas for Rb₂U(SO₄)₃, these values were found to be better than 4 and 13%, respectively.     

Analysis of low Z elements in various environmental samples with total reflection X-ray fluorescence (TXRF) spectrometry

Recently there is a growing interest in low Z elements such as carbon, oxygen up to sulphur and phosphorus in biological specimen. Total reflection X-ray fluorescence (TXRF) spectrometry is a suitable technique demanding only very small amounts of sample. On the other side, the detection of low Z elements is a critical point of this analytical technique. Besides other effects, self absorption may occur in the samples, because of the low energy of the fluorescence radiation. The calibration curves might be not linear any longer. To investigate this issue water samples and samples from human cerebrospinal fluid were used to examine absorption effects. The linearity of calibration curves in dependence of sample mass was investigated to verify the validity of the thin film approximation. The special requirements to the experimental setup for low Z energy dispersive fluorescence analysis were met by using the Atominstitute's TXRF vacuum chamber. This spectrometer is equipped with a Cr-anode X-ray tube, a multilayer monochromator and a SiLi detector with 30 mm² active area and with an ultrathin entrance window. Other object on this study are biofilms, living on all subaqueous surfaces, consisting of bacteria, algae and fungi embedded in their extracellular polymeric substances (EPS). Many trace elements from the water are bound in the biofilm. Thus, the biofilm is a useful indicator for polluting elements. For biomonitoring purposes not only the polluting elements but also the formation and growth rate of the biofilm are important. Biofilms were directly grown on TXRF reflectors. Their major elements and C-masses correlated to the cultivation time were investigated. These measured masses were related to the area seen by the detector, which was experimentally determined. Homogeneity of the biofilms was checked by measuring various sample positions on the reflectors.     

Element determination in medieval soil samples by total reflection X-ray fluorescence analysis

An aqua regia extraction procedure for heavy metals in soils optimised for total reflection X-ray fluorescence analysis is presented. The procedure is applied to 92 soil samples of medieval layers from the city area of Dortmund. Sixteen elements (P, S, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Ag, Sn, and Pb) were used to characterise 17 sample sites. The results are projected onto the medieval urban structure of Dortmund. Two sites loaded with non-ferrous heavy metal could be detected and correlated with archaeological data. The efficiency and repeatability of the proposed extraction procedure is discussed.     

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.     

Determination of trace elements in macrozoobenthos samples by total reflection X-ray fluorescence analysis

The paper describes the analysis of a set of metals in macrozoobenthos samples from a river in Western Austria by using total reflection X-ray fluorescence analysis (TXRF). Metal concentrations in aquatic insect larvae from an industrially contaminated site are significantly higher than in larvae from a reference site. Furthermore, species-specific differences in metal accumulation were found. TXRF allows multi-element analysis of very low metal concentrations in very small sample masses (e.g. single aquatic insect larvae with a dry weight of only a few milligrams). Due to its multi-element capability and high sensitivity total reflection X-ray fluorescence analysis is a valuable tool for biomonitoring studies of metal contamination in aquatic ecosystems.     

Determination of uranium in human urine by total reflection X-ray fluorescence

Uranium has been classified as a toxic chemical. It affects the kidneys, with nephritis being the primarily chemically-induced effect in animals and humans. Intermediate-term studies on animals indicate that increased uranium doses are positively correlated with various biochemical effects and histopathological changes. Since the kidneys efficiently excrete in urine the major portion of solubilized uranium circulating in blood, an increased urinary uranium excretion can provide a sensitive quantitative measure of exposure, especially in the case of acute exposure. In the present work a method was developed for the quantitative determination of uranium in human urine. It combines the chemical treatment of urine, which results in a significant pre-concentration of uranium, with its subsequent detection by means of total reflection X-ray fluorescence (TXRF). The method has been proven to be relatively fast, offering detection limits that allow for monitoring uranium intake above normal levels.