X-Ray fluorescence (XRF) is the emission of fluorescent X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. The X-ray fluorescence (XRF) method is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science and archaeology.

Applications of X-Ray Fluorescence Spectroscopy (XRF)

X-Ray fluorescence is used in a wide range of applications, including Quantitative analysis of bulk and trace elements in:

  • All metals and alloys (e.g. to check for conformity against specification)
  • XRF is a vital tool for RoHS Testing of electrical and electronic products to ensure RoHS compliance
  • Raw materials (e.g. mineral powders, oxides etc)
  • Glass (including major and minor components, colour elements etc)
  • Sputtered or plated layer thickness and/or composition
  • Routine process monitoring
  • Environmental studies (e.g., analyses of particulate matter on air filters, Environmental dust samples)
  • Waste acceptance Criteria and WAC testing
  • Composition of plating baths, solutions, effluent samples
  • Qualitative and semi-quantitative analysis of unknown materials and powders
  • Petroleum industry (e.g., sulfur content of crude oils and petroleum products)
  • Paints, adhesive, sealants and Gasket Filler materials fingerprinting.

Principle of X-Ray Fluorescence Spectroscopy (XRF)

The testing sample is irradiated with X-rays within the instrument. If an X-ray photon is absorbed by the testing sample of sufficient energy then an electron is emitted via the photoelectric effect resulting in an electron hole in the atom. An inner shell electron will then fall back to fill this hole resulting in the release of electromagnetic energy with a frequency characteristic of the element present.

The technique is quantitative and can be used on bulk powders, solids and liquids. Additionally it can be used on thin-film samples – e.g. filter papers used in environmental monitoring.

The X-Ray Fluorescence (XRF) method depends on fundamental principles that are common to several other instrumental methods involving interactions between electron beams and x-rays with samples, including: X-ray spectroscopy (e.g., SEM – EDS), X-ray diffraction (XRD), and wavelength dispersive spectroscopy (WDS).

Advantages of XRF

X-Ray fluorescence is particularly well-suited for investigations that involve:

  • bulk chemical analyses of trace elements (>1 ppm; Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, U, V, Y, Zr, Zn) in rock and sediment
  • bulk chemical analyses of major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) in rock and sediment

Limitations of XRF

In theory the XRF has the ability to detect X-ray emission from virtually all elements, depending on the wavelength and intensity of incident x-rays. However…

  • In practice, most commercially available instruments are very limited in their ability to precisely and accurately measure the abundances of elements with Z<11 in most natural earth materials.
  • XRF analyses cannot distinguish ions of the same element in different valence states, so these analyses of rocks and minerals are done with techniques such as wet chemical analysis or Mossbauer spectroscopy.
  • XRF analyses cannot distinguish variations among isotopes of an element, so these analyses are routinely done with other instruments (see TIMS and SIMS).