X Ray fluorescence spectrometry

The XRF technique has a true multi-element analysis capability and requires no foreknowledge of the elements present in the sample. As such it is very useful for the examination of many of the types of samples encountered in the plastics laboratory. 

This technique is very useful for solid samples especially if the main constituents (matrix) are made of low atomic weight elements and the sought impurities or constituents are of relatively high atomic weight. 

Typically, instruments will determine from a few percent down to parts per million in a solid sample. 

WDXRF tends to be most accurate and precise method for trace element determinations. EDXRF instruments tend to lose precision for traces of light elements in heavy element matrixes unless longer counting times are used. With short counting times, for example, the coefficient of variation for a minor constituent element determination by an energy 

Due to the simple spectra and the extensive element range (sodium upwards in the periodic table) that can be covered using an Si(Li) detector and a 50 kV X-ray tube, EDXRF spectrometry is perhaps unparalleled for its qualitative element analysis power. 

EDXRF instruments rely on solid-state energy detectors coupled to energy discriminating circuitry to distinguish the radiation by its energy level and measure the amount at each level. Most X-ray detectors now in use are solid-state devices which emit electrons when X-rays are absorbed, the energy of the electrons being proportional to that of the incident X-rays and the quantity proportional to the intensity. 

Samples are irradiated with high-energy radiation, usually X-rays, to produce secondary X-rays which are characteristic of the individual elements present. The 

Metal species detected by ion chromatography Detection limit (mg/1)  

In the laboratory, XRF analysis is usually performed in a vacuum chamber or in an atmosphere of an inert gas (like helium) so that low-energy photons are not absorbed by air. In general, the sensitivity of the method increases with the atomic number of the analyte and in solid samples the limit of detection for many elanents is typically in the mg kg (ppm) range. One advantage of the technique is the ability to perform a nondestructive assay of several elements simultaneously, although the accuracy for quantitative analysis is quite limited. Due to their simplicity and small size, handheld XRF devices are available and can be carried into the field for onsite analysis as described in detail recently (Bosco 2013). 

Alternative sources of primary X-rays now include synchrotron radiation (Pollard et al., 2007 290). The synchrotron is a large electron accelerator which produces electromagnetic radiation across the entire spectrum, with high spectral purity and very high beam intensity. At specific stations around the storage ring, particular sections of the electromagnetic spectrum are selected 

Beer s Law, the intensity of the beam [I(k)] after travelling a distance x through the solid is given by  

In an EDXRF system, the two tasks of energy measurement and detection are carried out simultaneously. In a WDXRF system, on the other hand, the 

In a competitive process, the excess energy can be dissipated by emission of a second or Auger electron from an outer shell of the atom, leaving it in a doubly ionised excited state. The relative importance of AES and XRF depends upon the atomic number (Z) of the element involved. High Z values favour fluorescence, whereas low Z favours AES. This fact, taken together with X-ray absorbance in air, makes XRF into a method which is not very sensitive for elements with atomic numbers below Z 10. Measurements of solid samples are normally made under vacuum, as the absorption of air renders analysis of elements lighter than Ti impossible. 

The sample format used for XRF measurement is typically compressed fine particle size powder (2-10 mm thick, 20-50 diameter), moulded film or 

Dynamic range Minimum detection limit Precision Accuracy 

Presence of neighbouring elements matrix effects no memory effects 

Relatively inexpensive (low power) to very expensive (high power spectrometers) 

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Elemental Analysis Atomic absorption spectrometry X-Ray fluorescence spectrometry Plasma emission spectrometry... 

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

Elemental chemical analysis provides information regarding the formulation and coloring oxides of glazes and glasses. Energy-dispersive x-ray fluorescence spectrometry is very convenient. However, using this technique the analysis for elements of low atomic numbers is quite difficult, even when vacuum or helium paths are used. The electron-beam microprobe has proven to be an extremely useful tool for this purpose (106). Emission spectroscopy and activation analysis have also been appHed successfully in these studies (101). 

AH of these properties of x-rays are used to measure various properties of materials. X-ray appHcations can be placed into three categories based on which of the above phenomena are exploited. These categories are x-ray radiography, x-ray fluorescence spectrometry, and x-ray diffraction. 

X-ray fluorescence spectrometry consists of the measurement of the incoherent scattering of x-rays (phenomenon 3 above). It is used primarily to determine the elemental composition of a sample. 

X-ray fluorescence spectrometry is a technique for measuring the elemental composition of samples. The basis of the technique is the relationship between the wavelength or energy of the emitted incoherently scattered x-ray photons and the atomic number of the element. This relationship estabHshed in 1913 is... 

Zinc smelters use x-ray fluorescence spectrometry to analyze for zinc and many other metals in concentrates, calcines, residues, and trace elements precipitated from solution, such as arsenic, antimony, selenium, tellurium, and tin. X-ray analysis is also used for quaUtative and semiquantitative analysis. Electrolytic smelters rely heavily on AAS and polarography for solutions, residues, and environmental samples. 

The determination of cesium in minerals can be accompHshed by x-ray fluorescence spectrometry or for low ranges associated with geochemical exploration, by atomic absorption, using comparative standards. For low levels of cesium in medical research, the proton induced x-ray emission technique has been developed (40). 

GENERALIZED DESCRIPTION OF POWDER AND POWDER SLURRY-LIKE MATERIALS IN X-RAY FLUORESCENCE SPECTROMETRY... 

Among the vitally necessary elements the most important are Fe, Zn, K, Ca, S. Some of them are imbedded in the stmcture of many ferments, amino acids, intracellular liquid, the other define transmembrane electrical potential. In the paper the contents of elements in whole blood and semm by X-ray fluorescence spectrometry is studied. 

Tetra-alkyl lead compounds in air Personal monitoring with atomic absorption analysis or electrothermal atomization or X-ray fluorescence spectrometry or on-site colorimetry 9... 

MDHS 7 Lead and inorganic compounds of lead in air (X-ray fluorescence spectrometry)... 

FCC feedstocks contain sulfur in the form of organic-sulfur compounds such as mercaptan, sulfide, and thiophenes. Frequently, as the residue content of crude oil increases, so does the sulfur content (Table 2-5). Total sulfur in FCC feed is determined by the wavelength dispersive x-ray fluorescence spectrometry method (ASTM D-2622), The results are expressed as elemental sulfur. 

Nineteen bone samples were prepared for analysis of the trace elements strontium (Sr), rubidium (Rb), and zinc (Zn). The outer surface of each bone was removed with an aluminum oxide sanding wheel attached to a Dremel tool and the bone was soaked overnight in a weak acetic acid solution (Krueger and Sullivan 1984, Price et al. 1992). After rinsing to neutrality, the bone was dried then crushed in a mill. Bone powder was dry ashed in a muffle furnace at 700°C for 18 hours. Bone ash was pressed into pellets for analysis by x-ray fluorescence spectrometry. Analyses were carried out in the Department of Geology, University of Calgary. 

Method abbreviations D-AT-FAAS (derivative flame AAS with atom trapping), ETAAS (electrothermal AAS), GC (gas chromatography), HGAAS (hydride generation AAS), HR-ICP-MS (high resolution inductively coupled plasma mass spectrometry), ICP-AES (inductively coupled plasma atomic emission spectrometry), ICP-MS (inductively coupled plasma mass spectrometry), TXRF (total reflection X-ray fluorescence spectrometry), Q-ICP-MS (quadrapole inductively coupled plasma mass spectrometry)... 

Morrison JL, Richardson JM (1996) Preliminary assessment of barium determination in Zinn-waldite ZW-C by X-ray fluorescence spectrometry. Geostds Newslett 20 65-69. 

Taggart JE Jr, Lindsay JR, Scott BA, Vivit DV, Bartel AJ, Stewart K C (1993) Analysis of geological materials by wavelength-dispersive X-ray fluorescence spectrometry. In Badecker PA, ed. U.S. Geological Survey Bulletin 1770. Methods for Geochemical Analysis, pp E1-E19. 

Table 8.38 Main features of wavelength-dispersive X-ray fluorescence spectrometry (WDXRF)...

R. Jenkins, X-Ray Fluorescence Spectrometry, Wiley-Intersdence, New York, NY (1999). 

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