Optimisation of total-reflection X-ray fluorescence for aerosol analysis

The capabilities of total-reflection X-ray fluorescence (TXRF) analysis were investigated to develop an efficient, simple, rapid and low cost analytical method for aerosols. The technique involves direct impaction of airborne particulate matter on the quartz sample-reflector discs for TXRF. Special attention was paid to bounce-off effects, and hence the aerosol size distributions for the impactor stages; influence of siliconizing the quartz discs on the adhesion of particles; choice of the internal standard; local distribution of the material deposited on the quartz disc; and alternative materials for aerosol collection. Moreover, the proposed method could be used in combination with a one-stage impactor for total aerosol mass collection and analysis.     

Development of suitable plastic standards for X-ray fluorescence analysis

For the adoption of the EU directive “Restriction on use of certain Hazardous Substances” and “Waste Electrical and Electronic Equipment” using X-ray fluorescence analysis suitable standard materials are required.     

X-ray fluorescence spectrometry for high throughput analysis of atmospheric aerosol samples: The benefits of synchrotron X-rays

The determination of trace element mass concentrations in ambient air with a time resolution higher than one day represents an urgent need in atmospheric research. It involves the application of a specific technique both for the aerosol sampling and the subsequent analysis of the collected particles. Beside the intrinsic sensitivity of the analytical method, the sampling interval and thus the quantity of collected material that is available for subsequent analysis is a major factor driving the overall trace element detection power. This is demonstrated for synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) of aerosol samples collected with a rotating drum impactor (RDI) in hourly intervals and three particle size ranges. The total aerosol mass on the 1-h samples is in the range of 10 µg. An experimental detection of the nanogram amounts of trace elements with the help of synchrotron X-rays was only achievable by the design of a fit-for-purpose sample holder system, which considered the boundary conditions both from particle sampling and analysis. A 6-µm polypropylene substrate film has evolved as substrate of choice, due to its practical applicability during sampling and its suitable spectroscopic behavior. In contrast to monochromatic excitation conditions, the application of a ‘white’ beam led to a better spectral signal-to-background ratio. Despite the low sample mass, a counting time of less than 30 s per 1-h aerosol sample led to sufficient counting statistics. Therefore the RDI-SR-XRF method represents a high-throughput analysis procedure without the need for any sample preparation. The analysis of a multielemental mass standard film by SR-XRF, laboratory-based wavelength-dispersive XRF spectrometry and laboratory-based micro XRF spectrometry showed that the laboratory-based methods were no alternatives to the SR-XRF method with respect to sensitivity and efficiency of analysis.     

X-ray Peltier cooled detectors for X-ray fluorescence analysis

The recent results on development of X-ray Si(Li), Si-planar and CdTe p-i-n detectors cooled by Peltier coolers for fabrication of laboratory and portable XRF analysers for different applications are discussed.

Low detection limits of XRF analysers are provided by increasing of detectors sensitive surface; improvement of their spectrometrical characteristics; decreasing of front-end-electronics noise level; Peltier coolers and vacuum chambers cooling modes optimization.

Solution of all mentioned tasks allowed to develop Peltier cooled detectors with the following performances:

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Advantages and disadvantages of all types of detectors for X-ray fluorescence analysis are compared. Spectra are presented. Application of different XRF analysers based on developed detectors in medicine, environmental science, industry, cryminalistics and history of art are demonstrated.     

Design of a doubly-curved crystal to improve X-ray fluorescence analysis of aerosol particles

Doubly-curved crystals (DCCs) can be very useful devices to focus and monochromatize radiation from an X-ray tube or a synchrotron, especially for X-ray fluorescence analysis. However, production of a DCC is somewhat difficult. In this paper we will present some basic theory about DCC geometries, different ways of DCC production and methods to test the quality of the DCCs.     

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.     

Extended fine structure in characteristic X-ray fluorescence: A novel structural analysis method of condensed systems

An oscillation similar to that in extended X-ray absorption fine structure (EXAFS) is found in characteristic X-ray fluorescence spectra, originating from a quantum interference effect during the X-ray emission process in a solid. We observe the oscillating fine structure in the radiative Auger X-ray fluorescence spectra of aluminum metal. The Al-Al interatomic distances are successfully reproduced by the Fourier transform of the fine structure. Thus, the present method has the potential to become a convenient alternative to EXAFS measurement for light elements.     

Energy-dispersive X-ray fluorescence spectrometer for analysis of conventional and micro-samples: Preliminary assessment

The energy-dispersive X-ray fluorescence spectrometer for analysis of conventional and micro-samples using pinhole collimators of various sizes is developed. The measurements can be performed in the air or, in order to decrease the absorption of long-wavelength radiation of low-Z elements, in helium atmosphere. The sample is excited by the air-cooled Rh target X-ray tube of ca. 100 μm nominal focal spot size and maximum power 75 W. The X-ray spectra of the samples are collected by thermoelectrically cooled Si-PIN detector. The tungsten pinhole collimators of the size holes from 50 to 2000 μm are placed between primary filter and analyzed sample to reduce size of analyzed area. The sample can be moved using the X–Y stage. The position of the sample is monitored by CCD camera and two laser pointers. The beam spot sizes for various collimators are evaluated by the thin-wire and knife-edge methods. Beside the beam spot sizes, the loss of radiation intensity and the changes of spectral distribution of the incident radiation caused by applying various collimators are also investigated. The sample-surface-down geometry in the designed spectrometer allows for a simple analysis of various samples: solutions, loose powders, solid samples of conventional size and micro-samples.     

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

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

Application of energy dispersive X-ray fluorescence spectrometry as multielemental analysis to determine the elemental composition of crumb rubber samples

The elemental content of different rubber samples was analyzed using different analytical methods (inductively coupled atomic emission spectroscopy and non-polarized energy dispersive X-ray fluorescent spectroscopy). A new application of energy dispersive X-ray spectrometry as an analytical method for the determination of elemental content of rubber samples was investigated. Control analyses were also carried out to compare the results by ICP-AES. In one hand four samples contained same quality of elements (Mg, Si, P, S, Ca, Fe, Zn), while another four samples were without phosphorous. On the other hand there were significant differences in the ratio of C/H in the case of each sample. Based on the results, it was concluded that the X-ray spectrometry as an analytical method is well-applicable to determine the elemental composition of rubber samples, but the calibration is a key part of the analysis. A good correlation was observed between the different methods, but the correlation was the function of characteristic of matrices. Significant matrix effect from the presence of phosphor was observed in the case of some samples, while the change of C/H ratio could not result notable matrix effect.     

X-ray fluorescence spectrometric analysis of erbium oxide for rare earth impurities

An X-ray fluorescence spectrometric method has been developed for the analysis of high purity erbium oxide for the determination of yttrium, terbium, dysprosium, holmium, thulium, ytterbium and lutetium oxide impurities in the concentration range 0.005–0.1%. The sample is taken in oxalate form, mixed with a binder (boric acid) in the weight ratio 31 and made into a double layer pellet. The analysis is done on a Philips PW 1220 X-ray fluorescence spectrometer using a LiF (200) analyzing crystal. The precision at each concentration of the standards and theoretical minimum detection limit for each element has been calculated.     

A routine gas chromatographic method for the analysis of chlorofluorocarbons in aerosol cans

Summary A gas chromatographic (GC) method for the routine analysis of fully halogenated chlorofluorocarbons (CFCs) in aerosol cans is described. The identification of CFCs by GC was found to be in full agreement with those by GC-mass-spectrometery. The method has been applied to the analysis of CFCs in 448 aerosol products. The most commonly used fully halogenated CFC propellants in aerosol cans were found to be CFC11, CFC12 and CFC114.     

Characterization of atmospheric aerosols using Synchroton radiation total reflection X-ray fluorescence and Fe K-edge total reflection X-ray fluorescence-X-ray absorption near-edge structure

In this study a new procedure using Synchrotron total reflection X-ray fluorescence (SR-TXRF) to characterize elemental amounts in atmospheric aerosols down to particle sizes of 0.015 um is presented. The procedure was thoroughly evaluated regarding bounce off effects and blank values. Additionally the potential of total reflection X-ray fluorescence–X-ray absorption near edge structure (SR-TXRF-XANES) for speciation of FeII/III down to amounts of 34 pg in aerosols which were collected for 1 h is shown. The aerosols were collected in the city of Hamburg with a low pressure Berner impactor on Si carriers covered with silicone over time periods of 60 and 20 min each. The particles were collected in four and ten size fractions of 10.0–8.0 μm, 8.0–2.0 μm, 2.0–0.13 μm 0.13–0.015 μm (aerodynamic particle size) and 15–30 nm, 30–60 nm, 60–130 nm, 130–250 nm, 250–500 nm, 0.5–1 μm, 1–2 μm, 2–4 μm, 4–8 μm, 8–16 μm. Prior to the sampling “bounce off” effects on Silicone and Vaseline coated Si carriers were studied with total reflection X-ray fluorescence. According to the results silicone coated carriers were chosen for the analysis. Additionally, blank levels originating from the sampling device and the calibration procedure were studied. Blank levels of Fe corresponded to 1–10% of Fe in the aerosol samples. Blank levels stemming from the internal standard were found to be negligible.     

A gas chromatographic-mass spectrometric method for trace analysis of chlorofluorocarbons and their replacement compounds in atmospheric samples

Summary The simultaneous determination of chlorofluorocarbons and their replacement compounds in ambient air samples requires the preconcentration of appropriate air volumes on suitable adsorbents. The performance of a dual-layer adsorption tube to be used in this type of analysis was evaluated in terms of breakthrough volumes (BTV) for the compounds of interest at ambient temperature. To verify the effectiveness of such adsorption tubes, real air samples were enriched at ambient temperature and were subsequently analyzed by capillary gas chromatography coupled with quadrupole mass spectrometry, operating in SIM mode. The results obtained confirmed the efficacy of the proposed method, in terms both of sensitivity and chromatographic separation efficiency.     

Automated energy-dispersive X-ray fluorescence analysis of environmental samples

Summary A procedure is described for the routine automatic analysis of 20 elements in small environmental samples. Up to 50 samples a day can be processed. The instrument uses an energy dispersive X-ray spectrometer for the simultaneous detection of all elements during a 5–20 min measurement. Computer techniques are used for the subsequent data reduction of the X-ray spectra. The technique is applicable to air particulate matter filtered from the air, to suspended material in water which is filtered on a filter paper and to dissolved trace elements which are evaporated on filter paper or are collected on a thin ion-exchange loaded paper.

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Automatisierte energie-dispersive Röntgenfluorescenzanalyse von Umweltmaterial

Zusammenfassung Ein Verfahren zur automatischen Routinebestimmung von 20 Elementen in Umweltmaterial wird beschrieben. Bis zu 50 Proben je Tag können verarbeitet werden. Ein energie-dispersives Röntgenspektrometer wird zur simultanen Erfassung aller Elemente bei einer Messung von 5–20 min benutzt. Die nachfolgende Auswertung der Spektren wird mittels Computer durchgeführt. Das Verfahren findet Anwendung auf Schwebestaub oder in Wasser suspendierte Substanzen, die auf Filterpapier gesammelt wurden sowie auf gelöste Elementspuren, die auf Filterpapier getrocknet oder durch Ionenaustauschpapier angereichert wurden.

     

X-ray fluorescence spectrometry applied to the analysis of environmental samples

X-ray fluorescence spectrometry is an expanding technique in the field of environmental analysis for both air and water pollution studies. Its capabilities now include the determination of gaseous contaminants in air in addition to the established area of elemental analysis, covering airborn particulates and soluble trace elements in water.     

A gas chromatographic-mass spectrometric method for analysis of the contents of aerosol irritant projectors

A convenient method for the sampling and total analysis of the propellents and active agents contained in aerosol irritant projectors has been developed. A gas chromatograph equipped with a column packed with 6% Carbowax 20M on Chromosorb G and coupled to a mass spectrometer provides both quantitative and qualitative analysis for the components of a typical irritant projector. The main lachrymator, bromoacetone, represented 1.5% and the propellents dichlorodifluoromethane and trichlorofluoromethane, comprised 97.7% of the aerosol mixture.     

X-ray fluorescence as a method of monitoring metal catalyst content during the purification of carbon nanotubes

There have been several studies that suggest that catalyst metals in carbon nanotubes (CNTs) may pose a health threat. As there are many potential applications of CNTs in medicine, it is important to be able to quantitatively determine the amount of metal catalyst contained in a CNT sample. The relative catalyst content of carbon nanotube samples synthesized via arc-discharge has been determined at various stages of the purification process using X-ray fluorescence (XRF) analysis. Purification was achieved by immersing samples in heated nitric acid. The intensities of the nickel K_α X-rays were studied to determine the relative catalyst content in the samples. Scanning electron microscopy (SEM) images of purified nanotubes have been compared to the images of a sample that has been irradiated by 0-15 keV bremsstrahlung in order to determine if the XRF analysis of the nanotubes is in any way destructive. No obvious structural defects were observed as the result of irradiation.