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.     

Total reflection X-ray fluorescence analysis of river waters in its stream across the city of Cordoba,in Argentina

The aim of this work was to analyze the composition of river waters and to study their quality by detecting possible contaminants. The samples were taken at 32 points of the Suquía River in its stream across the city of Córdoba (in the Province of Córdoba, Argentina). The samples were analyzed with total reflection X-ray fluorescence (TXRF) using beam guides. Beam guides made of two Si plate reflectors were used as sample carriers and to guide the X-ray photons to the sample; the measurements were taken using the characteristic configuration that ensures the best excitation and detection conditions (in TXRF). The analyses were carried out by preconcentration of the water samples and by adding an internal standard (Gallium); small amounts of samples (30 μl) were deposited on the Si reflector plate and they were then analyzed in the total reflection regime. Spectra were analyzed with standard methods using conventional programs. The results show interesting behaviors of the concentration of trace elements along the river: elements of low atomic number (such as Ca, Cl, S, K) present higher concentrations as compared to high Z elements (such as Fe, Zn, Br, Sr); the concentrations of light elements follow a similar behavior along the stream, the same situation is observed in the set of elements with high atomic number. Some samples present high concentrations in certain elements indicating possible sources of contamination.     

Determination of trace impurities in electronic grade quartz: Comparison of inductively coupled plasma mass spectroscopy with other analytical techniques

An analytical procedure for the determination of uranium and thorium in the sub-ng/g range as well as of other trace elements in the ng/g to g/g range in high purity quartz samples is described. The results obtained by inductively coupled plasma mass spectroscopy (ICP-MS) are compared to those obtained by other analytical techniques (instrumental neutron activation analysis, INAA; flame atomic absorption spectrometry, AAS; Zeeman graphite furnace atomic absorption spectrometry, ZGFAAS; total reflection X-ray fluorescence analysis, TRFA; direct current arc optical emission spectrometry, DC-arc OES; and X-ray fluorescence analysis, XRFA). For the ICP-MS measurements, the decomposition of the samples is carried out with HF/HNO₃/H₂SO₄-mixtures. The results obtained by the different methods show reasonable agreement. For uranium and thorium, ICP-MS proves to be the most sensitive method: detection limits of about 50 pg/g can be achieved for both elements.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Analysis of elemental concentration censored distributions in breast malignant and breast benign neoplasm tissues

The total reflection X-ray fluorescence method was applied to study the trace element concentrations in human breast malignant and breast benign neoplasm tissues taken from the women who were patients of Holycross Cancer Centre in Kielce (Poland). These investigations were mainly focused on the development of new possibilities of cancer diagnosis and therapy monitoring. This systematic comparative study was based on relatively large (∼ 100) population studied, namely 26 samples of breast malignant and 68 samples of breast benign neoplasm tissues. The concentrations, being in the range from a few ppb to 0.1%, were determined for thirteen elements (from P to Pb). The results were carefully analysed to investigate the concentration distribution of trace elements in the studied samples. The measurements of concentration of trace elements by total reflection X-ray fluorescence were limited, however, by the detection limit of the method. It was observed that for more than 50% of elements determined, the concentrations were not measured in all samples. These incomplete measurements were treated within the statistical concept called left-random censoring and for the estimation of the mean value and median of censored concentration distributions, the Kaplan–Meier estimator was used. For comparison of concentrations in two populations, the log-rank test was applied, which allows to compare the censored total reflection X-ray fluorescence data. Found statistically significant differences are discussed in more details. It is noted that described data analysis procedures should be the standard tool to analyze the censored concentrations of trace elements analysed by X-ray fluorescence methods.     

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.     

Improvement of total reflection X-ray fluorescence analysis of low Z elements on silicon wafer surfaces at the PTB monochromator beamline for undulator radiation at the electron storage ring BESSY II

Several different total reflection X-ray fluorescence (TXRF) experiments were conducted at the plane grating monochromator beamline for undulator radiation of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II, which provides photon energies between 0.1 and 1.9 keV for specimen excitation. The lower limits of detection of TXRF analysis were investigated for some low Z elements such as C, N, O, Al, Mg and Na in two different detection geometries for various excitation modes. Compared to ordinary XRF geometries involving large incident angles, the background contributions in TXRF are drastically reduced by the total reflection of the incident beam at the polished surface of a flat specimen carrier such as a silicon wafer. For the sake of an application-oriented TXRF approach, droplet samples on Si wafer surfaces were prepared by Wacker Siltronic and investigated in the TXRF irradiation chamber of the Atominstitut and the ultra-high vacuum TXRF irradiation chamber of the PTB. In the latter, thin C layer depositions on Si wafers were also studied.     

Optimization of a glancing angle for simultaneous trace elemental analysis by using a portable total reflection X-ray fluorescence spectrometer

By using a portable total reflection X-ray fluorescence spectrometer with a 1 W X-ray tube, a specimen containing nanograms of Ca, Sc, Ti, V, Cr, Mn, Fe, and Ni is measured at several glancing angles of incident X-rays. Continuum X-rays are used as the excitation source. The intensities of the spectral background which degrades sensitivity to trace elements are decreased with a decrease of the glancing angle, and all these elements are detected at the glancing angle of 0.13° smaller than the critical angle for total reflection of the incident X-rays (0.20°). An optimum glancing angle for simultaneously detecting these trace elements is around 0.13°, and detection limits at 0.13° are sub-nanograms to ten nanograms.     

Total reflection X-ray fluorescence analysis of Mongolian coals

Coal samples were analysed for trace elements using total reflection X-ray fluorescence with monochromatic excitation. The procedure involved direct irradiation of the sample with the incoherent peak as internal standard. A new method for spectrometer sensitivity determination and sample quantification, was evaluated. Variable amounts of several trace elements were obtained in the analysis of coal from eight different deposits of Mongolia. The accuracy of the procedure was verified with the analysis of a coal standard.     

Elemental composition of drinking water supplies in three states in Southeastern Nigeria

The levels of some trace elements; Co, Mn, Cu, Zn, Cr, Cd, Pb, Fe, Hg, Se, As, Ni and minor elements; Na, K, Ca and Mg were determined in public drinking water supplies (public taps and groundwaters) in three states in Southeastern Nigeria using energy dispersive X-ray fluorescence spectrometry (EDXRF) and flame atomic absorption spectrometry (FAAS). The mean levels of most of the trace elements in the groundwater samples were below the World Health Organization (WHO) drinking water quality limits, the only exception being Hg whose mean value of 3.69 μg/l exceeded the WHO limit of 1.0 μg/l. Violations of the WHO limits were also observed for Fe, Zn, Se and Pb in some of the groundwater samples. In the public tap samples only Hg violated the WHO limit.     

Recent results of synchrotron radiation induced total reflection X-ray fluorescence analysis at HASYLAB,beamline L

At the Hamburger Synchrotronstrahlungslabor (HASYLAB), Beamline L, a vacuum chamber for synchrotron radiation-induced total reflection X-ray fluorescence analysis, is now available which can easily be installed using the adjustment components for microanalysis present at this beamline. The detector is now in the final version of a Vortex silicon drift detector with 50-mm² active area from Radiant Detector Technologies. With the Ni/C multilayer monochromator set to 17 keV extrapolated detection limits of 8 fg were obtained using the 50-mm² silicon drift detector with 1000 s live time on a sample containing 100 pg of Ni.Various applications are presented, especially of samples which are available in very small amounts: As synchrotron radiation-induced total reflection X-ray fluorescence analysis is much more sensitive than tube-excited total reflection X-ray fluorescence analysis, the sampling time of aerosol samples can be diminished, resulting in a more precise time resolution of atmospheric events. Aerosols, directly sampled on Si reflectors in an impactor were investigated. A further application was the determination of contamination elements in a slurry of high-purity Al₂O₃. No digestion is required; the sample is pipetted and dried before analysis. A comparison with laboratory total reflection X-ray fluorescence analysis showed the higher sensitivity of synchrotron radiation-induced total reflection X-ray fluorescence analysis, more contamination elements could be detected. Using the Si-111 crystal monochromator also available at beamline L, XANES measurements to determine the chemical state were performed. This is only possible with lower sensitivity as the flux transmitted by the crystal monochromator is about a factor of 100 lower than that transmitted by the multilayer monochromator. Preliminary results of X-ray absorption near-edge structure measurements for As in xylem sap from cucumber plants fed with As(III) and As(V) are reported. Detection limits of 170 ng/l of As in xylem sap were achieved.     

Matrix effect on the detection limit and accuracy in total reflection X-ray fluorescence analysis of trace elements in environmental and biological samples

The effect of matrix contents on the detection limit of total reflection X-ray fluorescence analysis was experimentally investigated using a set of multielement standard solutions (500 ng/mL of each element) in variable concentrations of NH₄NO₃. It was found that high matrix concentration, i.e. 0.1–10% NH₄NO₃, had a strong effect on the detection limits for all investigated elements, whereas no effect was observed at lower matrix concentration, i.e. 0–0.1% NH₄NO₃.     

Examination of steel samples, provided as reference materials, by instrumental analyses

Summary Seven steel samples considered as reference materials have been analysed by atomic emission spectrometry with inductively coupled plasma (ICP-AES), atomic absorption spectrometry with flame and graphite furnace atomization (FAAS, GFAAS), differential pulse anodic stripping voltammetry (DPASV), X-ray fluorescence analysis with total reflection sample carrier (TXRF), and instrumental neutron activation analysis (INAA). Totally, 18 elements were determined. Over 90% of all results were in good agreement with the values determined by wet analytical methods. The deviations can be explained by systematical errors for special elements in distinct methods and by statistical errors, mainly at very low concentrations because some elements, in the low ng/g region, are not homogeneously distributed in the given material.formerly: Amt für Standardisierung, Meßwesen und Warenprüfung, Große Steinernetischstrasse 4, DDR-3010 Magdeburg     

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.     

Multielementstandards auf Kieselgelbasis zur Bestimmung von Spurenelementen in silicatischen Proben durch R?ntgenfluorescenzanalyse

Zusammenfassung Die Herstellung von Multielementstandards auf Kieselgelbasis für die Bestimmung von Spurenelementen in silicatischen Gesteinen und Mineralien wird beschrieben. Der Einfluß auf die Fluorescenzintensität der Spurenelemente durch andere Spurenelemente wird untersucht. Matrixeffekte, bedingt durch leichte und mittelschwere Elemente, die in höheren Konzentrationen vorhanden sind, werden ebenfalls geprüft. Die Ergebnisse der Bestimmungen von Spurenelementen in verschiedenen geochemischen Referenzproben werden mit den gegebenen Richtwerten verglichen. In allen Fällen wird gute Übereinstimmung erzielt.

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Multielement standards on the basis of silica gel for the determination of trace elements in silicate samples by X-ray fluorescence analysis

Summary The preparation of multielement calibration standards based on silica gel for the determination of trace elements in rocks and minerals is described. The influence on the fluorescence intensity of trace elements by other trace elements is investigated. Matrix effects, caused by low and middle atomic number elements present in higher concentrations are also studied. Results of trace element determinations in various geochemical reference samples are compared with recommended values. In all cases good agreement is observed.

     

Determination of analytes at trace level in uranium matrix by ICP-AES without chemical/physical separation

Determination of trace metallic constituents in nuclear materials e.g. U, Pu, Am, Zr etc. by Atomic Emission Spectroscopy requires the separation of the major matrix without the loss of analytes at trace level. For DC Arc carrier distillation technique, carrier is used to separate the matrix physically according to the volatility of the analytes while appropriate extractant in suitable diluent is used for chemical separation in inductively coupled plasma atomic emission spectroscopy (ICP-AES). In the present study an attempt was made to develop a methodology for the determination of B, Cd, Mg, Zn, Al, Sr and Sc at trace level (up to 0.1 μg/mL) in uranium matrix without any chemical or physical separation. It involves identification of suitable analytical lines of uranium for its ICP-AES determination; study the spectral interference of uranium to choose interference free analytical lines, optimization of instrumental and experimental parameters etc. The method was validated using synthetic samples.     

Developing electrodeposition techniques for preconcentration of ultra-traces of Ni, Cr and Pb prior to arc-atomic emission spectrometry determination

Electrodeposition is known to be proper for separation and preconcentration of extremely low concentrations of analytes from the bulk sample which is instrumentally very simple. In the present research, a combination of electrodeposition with arc atomic emission spectrometry (ED-AAES) method has been developed in order to improve the analytical performance of this spectrometry technique. The results show that sensitivity and detection limits by using ED-AAES were improved 1000–2000 folds over those of normal arc atomic emission spectrometry in determination of the selected elements. The detection limits for measurement of Ni, Cr and Pb were 2.56, 3.05 and 2.11 µg L^{− 1} for monodeposition and 3.31, 3.72 and 3.25 µg L^{− 1} for simultaneously deposition, respectively. The precision of determination was in the range of 2–4% RSD. Typical calibration graphs for these elements were linear up to 100 µg L^{− 1}, depending on the element and matrix.Application of this technique was also tested on determination of the studied elements in an electroplating plant's waste water. The accuracy of technique was verified by comparing the results of the waste water analysis with those of electrothermal atomic absorption spectroscopy as a reference standard method.The obtained results show that the combined technique (ED-AAES) has been progressed substantially toward the ultimate goal of direct interference-free determination of trace analysis in complex samples by AAES.     

Analysis of human blood serum and human brain samples by total reflection X-ray fluorescence spectrometry applying Compton peak standardization

The method of using the Compton peak as internal standard in total reflection X-ray fluorescence (TXRF) determination is established for trace element determination of Fe, Cu, Zn, Se and Pt in human serum and of Cu and Zn in homogenized brain samples. A new method of spectrometer sensitivity calibration using spiked matrices with known amounts of trace elements is tested against established methods of matrix matching as well as internal element addition. The analytical results with the proposed procedure are compared to a certified international standard and to values with Atomic Absorption Spectrometry (AAS) obtaining analytical results of comparable accuracy and precision. The method is adequate for routine clinical analysis as it has the advantages of requiring very small amounts of material and simple preparations, which avoids the chemical digestion stage.     

Total reflection X-ray fluorescence trace mercury determination by trapping complexation: Application in advanced oxidation technologies

It is well known that Hg species cause high noxious effects on the health of living organisms even at very low levels (5 μg/L). Quantification of this element is an analytical challenge due to the peculiar physicochemical properties of all Hg species. The regulation of the maximal allowable Hg concentration led to search for sensitive methods for its determination. Total reflection X-ray fluorescence is a proved instrumental analytical tool for the determination of trace elements. In this work, the use of total reflection X-ray fluorescence for Hg quantification is investigated. However, experimental determination by total reflection X-ray fluorescence requires depositing a small volume of sample on the reflector and evaporation of the solvent until dryness to form a thin film. Because of volatilization of several Hg forms, a procedure to capture these volatile species in liquid samples by using complexing agents is proposed. Acetate, oxalic acid, ethylenediaminetetracetic acid and ammonium pyrrolidine–dithiocarbamate were assayed for trapping the analytes into the solution during the preparation of the sample and onto the reflector during total reflection X-ray fluorescence measurements. The proposed method was applied to evaluate Hg concentration during TiO₂-heterogeneous photocatalysis, one of the most known advanced oxidation technologies. Advanced oxidation technologies are processes for the treatment of effluents in waters and air that involve the generation of very active oxidative and reductive species. In heterogeneous photocatalysis, Hg is transformed to several species under ultraviolet illumination in the presence of titanium dioxide. Total reflection X-ray fluorescence was demonstrated to be applicable in following the extent of the heterogeneous photocatalysis reaction by determining non-transformed Hg in the remaining solution.     

Rapid laser fluorometric method for the determination of uranium in soil, ultrabasic rock, plant ash, coal fly ash and red mud samples

A simple and rapid laser fluorometric determination of trace and ultra trace level of uranium in a wide variety of low uranium content materials like soil, basic and ultra basic rocks, plant ash, coal fly ash and red mud samples is described. Interference studies of some common major, minor and trace elements likely to be present in different, geological materials on uranium fluorescence are studied using different fluorescence enhancing reagents like sodium pyrophosphate, orthophosphoric acid, penta sodium tri-polyphosphate and sodium hexametaphosphate. The accurate determination of very low uranium content samples which are rich in iron, manganese and calcium, is possible only after the selective separation of uranium. Conditions suitable for the quantitative single step extraction of 25 ng to 20 μg uranium with tri-n-octylphosphine oxide and single step quantitative stripping with dilute neutral sodium pyrophosphate, which also acts as fluorescence enhancing reagent is studied. The aqueous strip is used for the direct laser fluorometric measurement without any further pretreatment. The procedure is applied for the determination of uranium in soil, basalt, plant ash, coal fly ash and red mud samples. The accuracy of the proposed method is checked by analyzing certain standard reference materials as well as synthetic sample with known quantity of uranium. The accuracy and reproducibility of the method are fairly good with RSD ranging from 3 to 5% depend upon the concentration of uranium.     

Concentrations of major and trace elements in polished rice and paddy soils collected in Aomori,Japan

Rice grain samples and surface paddy soil samples were collected from 20 sites throughout Aomori Prefecture, Japan, and the concentrations of 25 elements in the polished rice and 33 elements in the soils were determined by neutron activation analysis, inductively coupled plasma-mass spectrometer or atomic adsorption spectrometer. The range of essential element concentrations in the polished rice was within one order of magnitude, however, the range for most of the trace elements was more than one order of magnitude. The range of element concentrations, except for I, in the paddy soils was within one order of magnitude. The ±95% confidence intervals of the soil-to-polished rice transfer factors for all elements, except for Pb, were within two orders of magnitude, and the geometric mean values were as follows: Cl, Mo and Zn (0.1–1); K, Cu, Cd, Rb, Mg, Mn, and Ag (0.01–0.1); Ni, As, Ca, Se and I (0.001–0.01); Na, Cs, Sr, Co, Cr, V, Ba, Pb, Fe and Al (<0.001).