Trace element analysis by particle and photon-induced X-ray emission spectroscopy

The analytical use of particle- and photon-induced X-ray emission spectroscopy has become an important tool in trace element analysis, especially when only small amounts of sample material are available. The physical basis, experimental procedure and typical examples are reviewed.     

The analysis of ruthenium catalysts by photon-induced X-ray fluorescence using a microcomputer for data acquisition and analysis

An improved method for the determination of ruthenium in catalytic materials based on a relative fluorescence ratio factor is presented. This method employs a thin-film technique and an internal standard technique to minimize absorption and enchancement effects. The samples and standards were fluorescent with a¹⁰⁹Cd (7 mCi) annular source for 200 seconds and the data were collected and analyzed with an Apple II+ micro computer. Precision (total variation) for typical ruthenium catalysts in the range of 1–5% ruthenium was about 2%. Finally, the concentration of ruthenium in six commercial catalysts was determined for both alumina and carbon supports.Parts of this work have been funded by an international program between CONICIT (Venezuela) and NSF (United States of America).     

Trace element analysis of waters by X-ray emission spectroscopy

X-ray emission spectroscopy is a rapid, simple and accurate method for multielement trace analysis of water. This is accomplished by trace elements precipitation with a nonspecific chelating agent APDC (ammonium-1-pyrollidine dithiocarbamate) and filtration through a Millipore filter. In that way the uniform targets suitable for X-ray analysis were made and elements in concentrations as low as few ppb could be determined. APDC chelation over broad pH ranges for different elements in seawater is discussed. The best pH range for simultaneous determination of these elements is found. Results of analysis of seawater samples taken near the island Krk in the Adriatic sea are presented.     

Proton-induced X-ray emission analysis of Jordanian cigarettes

Proton-induced X-ray emission spectroscopy was applied to determine the concentration of 11 elements in cigarette tobacco of four brands commercially made in Jordan, and one foreign brand. The results are expressed in absolute amount per cigarette. Cigarette wrapping paper and cigarette smoke were also analyzed. The significance of some of the elements found in the samples are discussed. Work carried out at the Department of Nuclear Physics, Lund Institute of Technology, Solvegatan 14, S-223 62, Lund, Sweden.     

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.     

X-ray emission from LiTaO3 induced by thermal changes and structure analysis

X-ray emission from LiTaO₃ induced by the thermal changes from about 300–480 K has been investigated in a vacuum system. The single-crystal X-ray structure analysis of LiTaO₃ was carried out at 269, 286, 303, 319, 337, 358, 381, 413, and 436 K, respectively, far below the phase transition (∼930 K). The relationship between the observed X-ray emission and the pyroelectric coefficient of LiTaO₃ is discussed.     

Particle-induced X-ray emission analysis of Eastern Indian ferromanganese oxide ores

Summary Ferromanganese oxide ore samples were studied from four different mines by particle-induced X-ray emission (PIXE) technique using 3 MeV proton beam obtained from a 3 MV pelletron accelerator at the Institute of Physics, Bhubaneswar, India. After irradiation, the spectral data were analyzed by a GUPIX-2000 software. Large number of major, minor and trace elements have been estimated in these samples. It has been observed that there is a positive correlation among manganese and some elements like Ca, Co, Pb, Zn and Se, whereas V and Mo correlates with iron well.     

Trace element study of human bone by X-ray emission analysis using an external proton beam

A simple proton beam (PIXE) arrangement developed for a low energy accelerator was used for the determination of absolute concentrations of nine trace elements in human bone samples. The 2.4 MeV proton beam was externalized through a thin (2 μm) aluminiummylar foil. Using an air cooling system, the foil withstood a high current (0.5–1 μA) for a long time. The samples were cooled to prevent damage and volatilization of elements. The induced X-rays were detected with a Si(Li) detector and the external beam was monitored with a second detector, measuring K X-rays induced in atmospheric argon. The mean (SD) trace element levels (ppm) measured in dense bone by comparison with hydroxyapatite/standard mixtures were: Cr<2.0, Mn<2.3, Fe 7.58 (1.55), Ni<2.4, Cu 3.58 (2.16), Zn 144 (27), Pb 12.2 (2.5), Br 12.4 (5.5) and Sr 47.7 (14.3). The detection limits for these elements achieved in this work were about 1 ppm when rather short measuring times (∼10 min) were used. The coefficient of variation of a single measurement, e.g. for Zn, was 3–4%. Because of the slow turnover of dense bone, such measurements provide a means of monitoring long term trace element exposure.     

Trace element analysis of maternal scalp hair by external beam proton-induced X-ray emission (PIXE)

We have constructed an external beam proton-induced X-ray emission (PIXE) system for trace element analysis of biological and environmental samples. Optimization of sample preparation and experimental PIXE set up has produced a rapid, accurate, sensitive, and reliable PIXE analysis procedure. The analytical procedure was evaluated using maternal scalp hair from pregnant women 16–19 weeks' gestation. The samples were irradiated with 3.5 MeV protons from the Rutgers Nuclear Physics Department's 8 MV Tandem FN Van de Graaff accelerator. The concentrations of the elements calcium (Ca) to cadmium (Cd) in hair are reported for 50 subjects. The analytical procedure is suitable for non-invasive clinical analysis for evaluation of nutritional states and for environmental exposure to toxic metals.     

Selenium determination in biological samples by X-ray emission spectroscopy

Determination of Se in blood serum by PIXE and XRF is presented. Two different sample preparation methods combined with two modes of sample excitation are compared. Both methods are shown to be suitable for Se determination in blood serum and in standard reference materials (horse kidney IAEA H-8 and bovine liver NBS 1577a).     

Determination of the elemental homogeneity of selected biological organs by 2MeV proton induced X-ray emission analysis

The use of finite size sub-samples to derive elemental concentrations which are representative of a tissue or organ as a whole are subject to errors arising from the heterogeneous nature of biological specimens. Proton induced X-ray emission (PIXE) analysis is employed to identify element variances in porcine liver, kidney and heart and sampling factors, which are the minimum mass of sample required to reduce concentration variability to a given level, are calculated. This analysis highlights the inhomogeneous nature of biological specimens and the need for clearly defined sampling protocols.     

X-ray emission spectroscopy of nitrogen-rich compounds

Nonresonant X-ray emission spectroscopy was used to compare the nitrogen-rich compounds ammonium nitrate, trinitrotoluene, and cyclotrimethylene-trinitramine. They are representative of crystalline and molecular structures of special importance in industrial and military applications. The spectral signature of each substance was analyzed and correlated with features in the electronic structure of the systems. This analysis was accomplished by means of theoretical simulations of the emission spectra and a detailed examination of the molecular orbitals and densities of states. We find that the two theoretical methods used (frozen-orbital density functional theory and real-space Green's function simulations) account semiquantitatively for the observed spectra and are able to predict features arising from distinct chemical complexes. A comparison of the calculations and the data provides insight into the electronic contributions of specific molecular orbitals, as well as the features due to bandlike behavior. With some additional refinements, these methods could be used as an alternative to reference compounds.     

Analytical use of proton-induced X-ray emission

Proton-induced X-ray emission, PIXE, is capable of simultaneous quantitative determination of 10–15 elements. An introduction to the physical properties of the method is given and detection limits are shown for a routine analysis of a thin aerosol sample. Examples of applications to both thick and thin samples are presented. Human tooth dentine is analysed for lead, with simple sample preparation, indicating lead values of a few ppm for Swedish children. Quantitative analyses of several other elements are obtained simultaneously. Cascade impactors are used for sampling aerosols in work environment during welding operations giving information of size distribution and concentrations of the elements present. The aerosol is dominated by particle sizes between 0.5 and 2 μm as measured by the impactor, but the size distributions are different for different elements and welding techniques and depend on the distance from the welding source. The relative abundance of the elements found in the aerosol indicates the presence of fractionation mechanisms.     

Determination of rare earth elements by radioisotope induced X-ray emission spectroscopy

A ring-shaped, 10⁹ Bq²⁴¹Am radioisotope source was used for the excitation of K-shell X-rays from rare earth elements (56<Z<64), present in powdered geological material. In order to improve the efficiency of the measurement of these elements in the concentration range down to 10 ppm, the optimum geometry of the system was found. The results obtained are presented and discussed.     

Influence of sample charging on satellite spectra during particle induced X-ray emission analysis

We demonstrate how the fine structures of particle induced X-ray emission spectra are influenced by build up of charge in insulating materials. We have measured silicon Kα satellite spectra emitted from fused quartz (SiO₂) that had been bombarded with 1.5 MeV He⁺ ions under various conditions of electron shower. For the insulating fused quartz, the diagram line (KL⁰) appears much stronger than the KLⁿ multiple-vacancy satellites (n ⩾ 1) making the satellites difficult to discern. However, when an electron shower is applied to the fused quartz, the diagram line is lowered according to shower conditions and the KL¹, KL² and KL³ satellites appear prominently. Emission of a strong diagram line from insulating fused quartz is principally due to the charging of the sample and its subsequent discharge.