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.     

X-ray fluorescence spectrometric determination of trace amounts of actinides on electrodeposited samples

A sensitive method is developed to determine traces of uranium, thorium and plutonium in effluent steams from nuclear fuel preparation and recycling facilities. Samples are prepared by electrodeposition of homogeneous, very thin actinide oxide layers on brass plates covered by a polished nickel surface. This procedure allows the aplication of α-spectrometric control measurements. Samples containing about 100 ng of actinide element are determined by x.r.f., which corresponds to actinide levels of 0.1 mg l^?1 in effluents under routine conditions. Simultaneous actinide determinations are possible. Fission products do not interfere.     

Application of radioisotope-excited X-ray fluorescence to the determination of trace elements in blood

A radioisotope-excited energy-dispersive X-ray fluorescence system has been constructed and used for the analysis of blood samples for trace elements. The possibility of determination of trace elements in blood by X-ray fluorescence based on comparison with standard reference materials has been outlined and the applicability of the method demonstrated by the analysis of blood samples. The method enables fast, non-destructive direct analyses to be carried out without lengthy sample pretreatment on a routine basis.     

X-ray fluorescence determinatin of trace elements in soil

Trace elements in soil are quantified by direct X-ray fluorescence method. Gallium is used an internal standard to compensate for variations in sample matrix, instrumental operating characteristics, and sample preparation. At the 50-mg kg^?1 level, V, Cr, Ni, Cu, Zn and As can be determined within a precision and accuracy of ± 20% or less. Sample prepartion is less elaborate than for some other methods.     

Excitation of X-ray fluorescence of massive samples by bremsstrahlung: Analytical possibilities of the monochromatic model

An algorithm was proposed for calculation of the equivalent analytical wavelength of the bremsstrahlung spectrum during X-ray fluorescence excitation in multicomponent objects of arbitrary thickness. A correlation is found between the analytically obtained approximate values of a given parameter and its exact values found numerically taking into account the design features of an X-ray tube. The approach makes it possible to minimize the error of the results of quantitative X-ray fluorescence analysis of samples of various thicknesses taking into account the matrix effects.     

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 novel total reflection X-ray fluorescence procedure for the direct determination of trace elements in petrochemical products

A total reflection X-ray fluorescence (TXRF) procedure was developed for the determination of metal traces in petrochemical end products or intermediates for surfactant synthesis. The method combines a fast and straightforward sample preparation, i.e. deposition on the sample holder and evaporation of the sample matrix, with an efficient quantification method based on internal standardization (organic gallium standard). The method developed showed detection limits below 0.05 μg g^-1 and in most cases below 0.005 μg g^-1. Fifteen elements (Ca, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Rh, Sn, Sr, V and Zn) were determined in matrices such as paraffins, n-olefins, linear alkylbenzenes, long-chain alkyl alcohols and esters: typical metal contents were below 1 μg g^-1. The results were compared with the reference method ASTM D5708 (test method B) based on inductively coupled plasma optical emission spectroscopy: advantages and drawbacks of the two procedures were critically evaluated. The TXRF method developed showed comparable precision and absence of bias with respect to the reference method. A comparison of the performances of the two methods is presented.     

Analysis of trace elements in medicinal plants with energy dispersive X-ray fluorescence

Mankind still depend on traditional herbal medicine for the treatment of various diseases and ailments. This paper discusses the elemental composition and concentration of medicinal plants investigated by energy dispersive X-ray fluorescence. The elements present in medicinal plants are P, Cl, K, Ca, S, Al, Ti, V, Rb, Sr, Zr, Nb, Mo, In, Sn, I and Ce. The physical basis of the used analytical method, the experimental set up and the procedure of sample preparation are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

An X-ray fluorescence method for gold determination in ore samples

A new method for gold determination in ore is presented. By the method called PREFIX (preconcentration and X-ray fluorescence), it is possible to detect trace concentrations of gold down to the level of 0.2 g/g, without any device.     

Partial least squares X-ray fluorescence determination of trace elements in sediments from the estuary of Nerbioi-Ibaizabal River

The feasibility of partial least squares (PLS) regression modeling of X-ray fluorescence (XRF) spectra of estuarine sediments has been evaluated as a tool for rapid trace element content monitoring. Multivariate PLS calibration models were developed to predict the concentration of Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V and Zn in sediments collected from different locations across the estuary of the Nerbioi-Ibaizabal River (Metropolitan Bilbao, Bay of Biscay, Basque Country). The study was carried out on a set of 116 sediment samples, previously lyophilized and sieved with a particle size lower than 63 μm. Sample reference data were obtained by inductively coupled plasma mass spectrometry. 34 samples were selected for building PLS models through a hierarchical cluster analysis. The remaining 82 samples were used as a test set to validate the models. Results obtained in the present study involved relative root mean square errors of prediction varying from 21%, for the determination of Pb at hundreds μg g⁻¹ level, up to 87%, for Ni determination at little tens μg g⁻¹ level. An average prediction error of ±37% for the 14 elements under study was obtained, being in all cases mean differences between predicted and reference results of the same order than the standard deviation of three replicates from a same sample. Residual predictive deviation values obtained ranged from 1.1 to 3.9.     

Novel modified carbon nanotubes as a selective sorbent for preconcentration and determination of trace copper ions in fruit samples

In this work, multiwalled carbon nanotubes were reacted with N‐[3‐(triet‐hoxysilyl)propyl]isonicotinamide to prepare pyridine‐functionalized carbon nanotubes. This novel sorbent was characterized by infrared spectroscopy, thermal and elemental analysis, and scanning electron microscopy. Functionalized carbon nanotubes were applied for the preconcentration and determination of copper ions using flame atomic absorption spectrometry. Various parameters such as sample pH, flow rate, eluent type and concentration, and its volume were optimized. Under optimal experimental conditions, the limit of detection, the relative standard deviation, and the recovery of the method were 0.65 ng/mL, 3.2% and 99.4%, respectively. After validating the method using standard reference materials, the new sorbent was applied for the extraction and determination of trace copper(II) ions in fruit samples.     

Direct determination of trace elements in boron nitride powders by slurry sampling total reflection X-ray fluorescence spectrometry

The use of slurry sampling total reflection X-ray fluorescence spectrometry (SlS-TXRF) for the direct determination of Ca, Cr, Cu, Fe, Mn and Ti in four boron nitride powders has been described. Measurements of the zeta potential showed that slurries with good stabilities can be obtained by the addition of polyethylenimine (PEI) at a concentration of 0.1 wt.% and by adjusting the pH at 4. For the optimization of the concentration of boron nitride in the slurries the net line intensities and the signal to background ratios were determined for the trace elements Ca and Ti as well as for the internal standard element Ga in the case of concentrations of boron nitride ranging from 1 to 30 mg mL⁻¹. As a compromise with respect to high net line intensities and high signal to background ratios, concentrations of 5 mg mL⁻¹ of boron nitride were found suitable and were used for all further measurements. The limits of detection of SlS-TXRF for the boron nitride powders were found to range from 0.062 to 1.6 μg g^– 1 for Cu and Ca, respectively. Herewith, they are higher than those obtained in solid sampling and slurry sampling graphite furnace atomic absorption spectrometry (SoS-GFAAS, SlS-GFAAS) as well as those of solid sampling electrothermal evaporation inductively coupled plasma optical emission spectrometry (SoS-ETV-ICP-OES). For Ca and Fe as well as for Cu and Fe, however, they were found to be lower than for GFAAS and for ICP-OES subsequent to wet chemical digestion, respectively. The universal applicability of SlS-TXRF to the analysis of samples with a wide variety of matrices could be demonstrated by the analysis of certified reference materials such as SiC, Al₂O₃, powdered bovine liver and borate ore with a single calibration. The correlation coefficients of the plots for the values found for Ca, Fe and Ti by SlS-TXRF in the boron nitride powders as well as in the before mentioned samples versus the reference values for the respective samples over a concentration range from 2.5 to 1470 μg g^– 1 were found to be 0.995, 0.991 and 0.997, respectively.     

X-ray fluorescence determination of uranium and neighbouring elements in solution

A method of energy dispersive X-ray fluofescence analysis of U, Np, Pu contents in solution has been developed for application in the field of VVER spent nuclear fuel reprocessing. Precision is 0.4% in the range of the U contents 0.2–2‰, and the detection limit is 0.15 ppm. Preliminary dilution is required for solutions with hihg U contents (>3‰). Spectra treatment program for a minicomputer has been developed and the method of corrections for non-linearity of concentration curves was checked.     

Application of NaClO-treated multiwalled carbon nanotubes as solid phase extraction sorbents for preconcentration of trace 2,4-dichlorophenoxyacetic acid in aqueous samples

Multiwalled carbon nanotubes functionalized by oxidation of original multiwalled carbon nanotubes with NaClO were prepared and their application as solid phase extraction sorbent for 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated systemically, and a new method was developed for the determination of trace 2,4-D in water samples based on extraction and preconcentration of 2,4-D with solid phase extraction columns packed with NaClO-treated multiwalled carbon nanotubes prior to its determination by HPLC. The optimum experimental parameters for preconcentration of 2,4-D, including the column activating conditions, the amount of the sorbent, pH of the sample, elution composition, and elution volume, were investigated. The results indicated 2,4-D could be quantitatively retained by 100 mg NaClO-treated multiwalled carbon nanotubes at pH 5, and then eluted completely with 10 mL 3:1 (v/v) methanol-ammonium acetate solution (0.3 mol/L). The detection limit of this method for 2,4-D was 0.15 μg/L, and the relative standard deviation was 2.3% for fortified tap water samples and 2.5% for fortified riverine water sample at the 10 μg/L level. The method was validated using fortified tap water and riverine water samples with known amount of 2,4-D at the 0.4, 10, and 30 μg/L levels, respectively.     

Multielement trace analysis of solid and liquid samples by X-ray fluorescence

Summary The use of energy-dispersive multielement X-ray analysis is described and the radionuclides¹⁰⁹Cd and²⁴¹Am and X-ray tubes combined with secondary targets are compared as X-ray sources. Solid powdered samples of infinite thickness are used without further treatment. Calibration standards are prepared from silica gel, and correction factors are derived from the peak heights of Compton scattering. Results for various geological samples and for dust samples are presented. Liquid samples are treated by means of a column or a filter with chelating groups bound to cellulose. A thin layer of the cellulose powder or the filter is analysed with the aid of calibration graphs. Results of multielement trace analysis of standardized water, river water and sea-water are presented and discussed.

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Zusammenfassung Die Anordnung für die energie-dispersive Multielement-Röntgenfluores-zenzanalyse einerseits mit Hilfe von Radionukliden (¹⁰⁹Cd und²⁴¹Am), andrerseits mit Röntgenröhren in Verbindung mit Sekundärtargets als Röntgenquellen wird beschrieben und verglichen. Feste Proben unendlicher Dicke werden in Pulverform ohne weitere Vorbehandlung verwendet. Die Eichung erfolgt mit Standardpräparaten, die aus Silicagel hergestellt werden und unter Anwendung eines Korrekturfaktors, der aus der Höhe der Peaks der Compton-Streuung abgeleitet wird. Ergebnisse für verschiedene geologische Proben und für Staub werden vorgelegt. Flüssige Proben werden mit einer Säulenmethode oder einer Filtermethode behandelt, wobei chelatbildende Gruppen auf Cellulose verwendet werden. Die dünne Schicht des Cellulosepulvers oder das Filter werden mit Hilfe von Eichkurven analysiert. Ergebnisse der Multielement-Spurenanalyse von standardisiertem Wasser, Leitungswasser, Flußwasser und Meerwasser werden vorgelegt und diskutiert.

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Presented at the International Symposium on Microchemical Techniques, May 23–27, 1977, Davos, Switzerland.     

Fast determination of trace elements on aerosol-loaded filters by X-ray fluorescence analysis considering the inhomogeneous elemental distribution

X-ray fluorescence (XRF) analysis was successfully applied for the determination of Ca, Cu, Fe, Mn, Ni, Pb, V and Zn on aerosol filters with a diameter of 150 mm. Ambient aerosol was collected on quartz-fibre filters by Digitel high-volume samplers. For XRF analysis three small filter pieces with a diameter of 32 mm were cut out of each filter, considering the radial dependence of elemental distribution on the filter. Elemental concentration decreases by 8-10% from the centre to the outer circle for coarse mode elements. Distribution of fine mode elements display only small radial dependence (2-4%). Results of quantitative analysis by XRF were compared with atomic spectrometric methods (GF-AAS, ICP-OES). The good agreement between the methods confirmed the application of XRF spectrometry for routine analysis of filter samples loaded with ambient aerosol.     

Radionuclide X-ray fluorescence analysis of selected elements in drug samples with 8-hydroxyquinoline preconcentration

The preconcentration performance characteristics of precipitation of Mn, Fe, Co, Cu, Zn, Pb, Ni and Hg with 8-hydroxyquinoline (8HQ) and subsequent filtration through cellulose nitrate membrane were investigated for the X-ray fluorescence spectrometry identification and determination of trace metal ions in drug samples. Several parameters of the method were optimised, including pH and amount of 8HQ. The investigated ions were collected on cellulose nitrate membrane filter (Pragopor 4) as their complexes after the reaction with 8HQ. To conclude, optimal reaction conditions were found out (pH 10.5 for Fe, Co and pH 11.5 for Mn, Cu Zn, Pb and Hg, volume of 20 μl of the 2 % solution of hydroxyquinoline). Thereafter, the content of these elements was determined in the active substances of the infusion and injection solutions, i.e. NaCl, glucose and dextrane, and the results were compared with those ones obtained after the preconcentration with thioacetamid. The rapidity of this method, its multi-element character and low detection limits proved this method to be a very promising in rapid screening in quality control of drugs.     

Possibilities and limitations of the total reflection X-ray fluorescence spectrometry for the determination of low Z elements in biological samples

The analytical capability of the laboratory scale vacuum total reflection X-ray fluorescence (TXRF) spectrometer (Wobistrax) was studied for the determination of the Z elements (Na, Mg, P, S, K and Ca) in different biological matrices represented by the following certified reference materials: MURST-ISS-A2 Antarctic krill, IAEA-331 spinach, NIST 1577a bovine liver, and SERONORM™ Trace Elements Serum Level 1.First, the stability of the response factors (relative sensitivity) against Ti internal standard was checked in the concentration range of 1 to 1000 mg/L in a diluted nitric acid matrix. It has been found that the upper limit of the analytical concentration range for K and Ca can be as high as 1000 mg/L; on the other hand, the remaining elements cannot be determined above a concentration of some tens mg/L.The established response factors were used for the elemental analysis of the four certified reference materials after normal-volume microwave assisted acid digestion. In the case of the serum sample, different preparation methods were compared as follow: direct analysis, microwave assisted acid digestion in normal-volume and micro-vessels, as well as the vapor-phase digestion directly on the TXRF carrier plates.On the basis of the results, the normal-volume digestion results in rather high dilution of the samples; thus, elements at low concentration could not be detected in some of the samples. On the other hand, this method offers the highest rate of both organic matrix decomposition and inorganic matrix dilution; thus, the background and the standard deviation of the results were the lowest. In general, this method was found to be useful for the analysis of samples with high dissolved (organic + inorganic) content if the analytes are present at a concentration considerable above the quantification limit.In the case of the microscale and the vapor-phase digestion, both the organic and inorganic matters remain at elevated concentration; thus, higher background and self-absorption of the fluorescent radiation occurred, deteriorating the analytical performance.     

Fast determination of trace elements on aerosol-loaded filters by X-ray fluorescence analysis considering the inhomogeneous elemental distribution

X-ray fluorescence (XRF) analysis was successfully applied for the determination of Ca, Cu, Fe, Mn, Ni, Pb, V and Zn on aerosol filters with a diameter of 150 mm. Ambient aerosol was collected on quartz-fibre filters by Digitel high-volume samplers. For XRF analysis three small filter pieces with a diameter of 32 mm were cut out of each filter, considering the radial dependence of elemental distribution on the filter. Elemental concentration decreases by 8–10% from the centre to the outer circle for coarse mode elements. Distribution of fine mode elements display only small radial dependence (2–4%). Results of quantitative analysis by XRF were compared with atomic spectrometric methods (GF-AAS, ICP-OES). The good agreement between the methods confirmed the application of XRF spectrometry for routine analysis of filter samples loaded with ambient aerosol.