X Ray Fluorescence spectrometer (XRF)

XRF Analysis Method

X-ray fluorescence or XRF analysis is the characteristic “secondary” (or fluorescent) emission of X-rays from a material that has been excited by bombardment with high-energy X-rays or gamma rays. XRF analysis is widely used for elemental and chemical analysis, particularly in the examination of metals, glass, ceramics, and building materials, as well as research in geochemistry, forensic science, archaeology, and art objects such as paintings.

How does XRF analysis work?

In XRF analysis, when materials are exposed to short-wavelength X-rays or gamma rays, ionization of their atoms may occur. Ionization involves the removal of one or more electrons from an atom and may occur if the atom is exposed to radiation with an energy greater than the ionization energy. X-rays and gamma rays can be energetic enough to knock tightly bound electrons out of the inner orbit of an atom. Removing an electron in this way makes the electronic structure of the atom unstable, and electrons in higher orbits “fall into lower orbits” to fill the remaining hole.

During the fall, energy is released in the form of a photon, the energy of which is equal to the energy difference between the two orbits involved. The material therefore emits radiation, which is characteristic of the energy of the atoms present. In XRF analysis, the term fluorescence is used for the phenomenon in which the absorption of radiation of a particular energy leads to the re-emission of radiation of a different (generally lower) energy.

What is X-ray fluorescence (XRF) analysis?

An X-ray fluorescence spectrometer (XRF) is an X-ray instrument used for routine and relatively non-destructive chemical analysis of rocks, minerals, sediments, and liquids. The method works on the principles of wavelength dispersive spectroscopy, which is similar to electron microprobe analysis (EPMA). However, an XRF analyzer generally cannot analyze the small sizes typical for EMPA, which are 2-5 microns in size, so XRF analysis is typically used to analyze larger fractions of geological materials. The relative ease and low cost of sample preparation and the stability and ease of use of XRF analysis make it one of the most widely used methods for analyzing major and trace elements in rocks, minerals, and sediments.

Specialized Applications of XRF Analysis

XRF analysis is used in a wide range of applications, including:

• Research in igneous, sedimentary and metamorphic petrology
• Soil investigation
• Cement production
• Ceramic and glass manufacturing
• Metallurgy (e.g., quality control)
• Environmental studies (e.g., particulate matter analysis in air filters)
• Petroleum industry (e.g., sulfur in crude oils and petroleum products)
• Fine analysis in geological and environmental studies

XRF analysis is suitable for investigations performed on:

• Bulk chemical analysis of major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) in rocks and sediments
• Bulk chemical analysis of trace elements with an abundance of less than 1 ppm (Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, U, V, Y, Zr, Zn) In rocks and sediments, detection of trace elements is usually in the order of a few parts per million.

What are the limitations of XRF analysis?

• Relatively large samples, typically greater than 1 gram
• Materials that can be prepared as powders and effectively homogenized
• Materials that are compositionally similar, with complete standards available
• Materials containing large amounts of elements for which absorption and fluorescence effects are well understood

Can XRF analysis be performed on powdered materials?

In most cases, for rocks, ores, sediments, and minerals, the sample is prepared as a fine powder. At this point, it may be analyzed directly, especially for trace element analysis. However, the very wide range of different elements, especially iron, and the wide range of samples in a powdered sample make it difficult to compare accurately with standards. For this reason, it is common to mix the powdered sample with a chemical flux and use a furnace or gas burner to melt the powdered sample. Melting a sample creates a homogeneous sample that can be analyzed and the abundance of elements (now somewhat diluted) calculated.