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Energy Dispersive X-ray Fluorescence (EDXRF) spectroscopy provides one of the simplest, most accurate and most economic elemental analytical methods for the determination of the chemical and/or elemental composition of many types of materials. The technique is generally non-destructive, requiring little if any sample preparation, and is suitable for almost all sample types. X-ray Fluorescence (XRF) spectrometric analysis can be employed to measure a wide range of atomic elements, from sodium (11) through uranium (92), while providing elemental detection limits from low parts-per-million (ppm) to high weight percent (%wt). In addition to elemental analysis, EDXRF spectrometers may be used to measure the thickness and composition of multi-layer thin films.

In X-ray fluorescence (XRF), an electron can be ejected from its atomic orbital by the absorption of a light wave (photon) of sufficient energy. The energy of the photon (hν) must be greater than the energy with which the electron is bound to the nucleus of the atom. When an inner orbital electron is ejected from an atom (middle image), an electron from a higher energy level orbital will be transferred to the lower energy level orbital. During this transition a photon maybe emitted from the atom (bottom image). This fluorescent light is called the characteristic X-ray of the element. The energy of the emitted photon will be equal to the difference in energies between the two orbitals occupied by the electron making the transition. Because the energy difference between two specific orbital shells, in a given element, is always the same (i.e. characteristic of a particular element), the photon emitted when an electron moves between these two levels, will always have the same energy. Therefore, by determining the energy (wavelength) of the X-ray light (photon) emitted by a particular element, it is possible to determine the identity of that element.

For a particular energy (wavelength) of fluorescent light emitted by an element, the number of photons per unit time (generally referred to as peak intensity or count rate) is related to the amount of that analyte in the sample. In EDXRF spectroscopy, the counting rates for all detectable elements within a sample are usually calculated by counting, for a set amount of time, the number of photons that are detected for the various analytes' characteristic X-ray energy lines. It is important to note that these fluorescent lines are actually observed as peaks with a semi-Gaussian distribution because of the imperfect resolution of modern detector technology. Therefore, by determining the energy of the X-ray peaks in a sample's spectrum, and by calculating the count rate of the various elemental peaks, it is possible to qualitatively establish the elemental composition of the samples and to quantitatively measure the concentration of these elements.

Rigaku X-ray spectrometers may be used in conjunction with Fundamental Parameters (FP) software to allow for elemental quantification of completely unknown samples without standards. For example, the Rigaku NEX CG energy dispersive X-ray fluorescence analyzer is powered by a new qualitative and quantitative analytical software, RPF-SQX, that features Rigaku Profile Fitting (RPF) technology. The software allows semi-quantitative elemental analysis of almost all sample types without standards – and rigorous quantitative analysis with standards.

Featuring Rigaku’s famous Scatter FP method, the software can automatically estimate the elemental concentration of unobserved low atomic number elements (H to F) and provide appropriate corrections. RPF-SQX greatly reduces the number of required standards, for a given level of calibration fit, as compared to conventional EDXRF spectrometric analytical software. As elemental analysis standards are expensive, and can be difficult to obtain for many applications, the utility of RPF-SQX can significantly lower the cost of ownership and reduce workload requirements for routine energy dispersive X-ray fluorescence based elemental analysis.

X-ray Transmission (XRT) gauging has long been an accepted technique for the measurement of sulfur (S) in heavy hydrocarbon process streams. Whether used for pipeline switching, crude oil blending or to assay or blend marine and bunker fuels, the Rigaku NEX XT XRT process analyzer is well suited to rigorous process environments, with pressures up to 1480 psig and temperature up to 200°C. X-ray transmission gauging involves measuring the attenuation of a monochromatic X-ray beam at a specific energy (21 keV) that is specific to sulfur (S). In practice, a process stream passes through a flowcell where sulfur (S), in the hydrocarbon matrix, absorbs X-rays transmitted between an X-ray source and detector. The recorded X-ray intensity is inversely proportional to the sulfur concentration, thus the highest sulfur levels transmit the least X-rays.

X-ray Transmission (XRT) gauging has long been an accepted technique for the measurement of sulfur (S) in heavy hydrocarbon process streams. Whether used for pipeline switching, crude oil blending or to assay or blend marine and bunker fuels, the Rigaku NEX XT XRT process analyzer is well suited to rigorous process environments, with pressures up to 1480 psig and temperature up to 200°C.

XRT Method
X-ray transmission gauging involves measuring the attenuation of a monochromatic X-ray beam at a specific energy (21 keV) that is specific to sulfur (S). In practice, a process stream passes through a flowcell where sulfur (S), in the hydrocarbon matrix, absorbs X-rays transmitted between an X-ray source and detector (see schematic at left). The recorded X-ray intensity is inversely proportional to the sulfur concentration, thus the highest sulfur levels transmit the least X-rays.

Transmission of X-rays through the flowcell is given by the following equation:

T=I/I_o=exp-dt[μ_m(1-C_s)+ μ_sC_s]

where:

  I = measured X-ray intensity (after flowcell, in photons/sec) 
  I_o = initial X-ray intensity (before flowcell, in photons/sec) 
  d = density of the hydrocarbon stream 
  t = thickness of the flowcell path (in cm) 
  μ_m = molar absorptivity for the hydrocarbon matrix @ 21 keV (cm²/gm) 
  μ_s = molar absorptivity for sulfur @ 21 keV (cm²/gm) 
  C_s = weight fraction of sulfur (% wt/wt)

Applied Rigaku Technologies, Inc. (ART) is a new research and development, manufacturing, sales, service and support subsidiary of Rigaku Americas Corporation dedicated to energy dispersive X-ray fluorescence (EDXRF) and related elemental analysis technologies.

This new U.S.-based "EDXRF Center of Excellence" is located in an all new 20,000 square foot facility in the northwest quadrant of Austin, Texas. As an affiliated company of the Rigaku XRF product group based in Osaka, Japan, ART will participate in the co-development of novel and cost-effective X-ray based analytical instruments and techniques to better serve the metrology requirements of the company's expanding global customer base. The objective of this innovative organization structure is to provide — industry, academe and governments — worldwide access to the latest in X-ray analytical technologies while delivering to customers a partnership-level service and support experience.

The company designs and manufacturers benchtop Energy Dispersive X-ray Fluorescence (EDXRF) elemental analysis instrumentation for non-destructive analytical chemistry applications, including atomic spectroscopy (spectrometry), quantitative and qualitative elemental analysis. Current instruments include the state-of-the-art polarized (cartesian geometry) Rigaku NEX CG EDXRF spectrometer and the new lost-cost Rigaku NEX QC EDXRF elemental analyzer. In addition, ART offers a 3rd generation X-ray Transmission (X-ray Absorption) process gauge for the determination of sulfur (sulphur) in a wide variety of heavy viscous hydrocarbon matrices, including bunker fuels, crude oil, and residuums.