XRF analysis
X-ray fluorescence (XRF) is an analytical method that is widely used to determine the elemental composition of rocks, minerals, cement, ceramics, metals, and petroleum. XRF analysis is based on the characteristic wavelengths of X-rays emitted by the atoms in the sample.
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What is XRF analysis used for?
XRF is a non-destructive analytical method commonly used to identify and determine the concentrations of both major and minor elements within a sample. XRF can be used in geophysical soil surveys, mining, and environmental studies, as well as in product development and quality control in industries including metallurgy, petroleum, cement, ceramics, and glass.
How does X-ray fluorescence work?
In XRF analysis, the sample is irradiated with a high-energy X-ray beam. While some of the X-rays scatter from the sample (see a comparison between XRF and XRD below), some are absorbed by the atoms in the sample and the atoms start emitting fluorescent light. The emitted fluorescent X-ray energy is characteristic of the specific element being analyzed. This is the key principle of XRF which makes it a fast and accurate analytical tool for elemental composition analysis.
Two modes of XRF are commonly applied: energy-dispersive X-ray fluorescence (EDXRF) and wavelength-dispersive X-ray fluorescence (WDXRF). EDXRF directly measures the energies of the emitted X-rays from the sample. It is used for fast identification and quantification of elements and requires minimal sample preparation. In WDXRF, a crystal is used to diffract the incoming X-rays in different directions, allowing for the separation of elements based on their wavelengths. The higher resolution of WDXRF provides improved detection limit and sensitivity, at the expense of longer analysis times and higher instrument prices.
Difference between XRF and XRD
When the sample is irradiated with the X-rays, some of them are absorbed in the atoms, and some scatter. X-ray fluorescence utilizes the absorbed X-rays and the fluorescent light that the absorption creates, while X-ray diffraction analyzes the diffraction patterns produced by the scattered X-rays.
XRF is most often used in environmental studies of rocks and minerals and for quality control in metallurgy and fossil fuels. XRD can be used to analyze crystalline minerals, but it is also used on polymers, pharmaceuticals, and food products. See the X-ray diffraction method page for further information.
XRF and XRD are complementary methods and are usually performed together to identify the elements, impurities, and phases of the samples as a whole. This approach is commonly employed for substance identification under EU chemicals legislation, including REACH submissions.
Sample requirements and preparation
XRF can be used to characterize powders, solids, and liquids. Solid samples are usually cut and polished to achieve a smooth surface or crushed to a fine powder. The loose powder samples can be analyzed as they are, or they can be pressed into pellets. Grinding and pelletizing the powders for XRF yields more homogeneous samples compared to loose powders. If the powder has a wide range of elements and grain sizes, the sample can be mixed with a chemical flux and melted in a furnace or with a gas burner to get accurate results. Melting produces a homogenous, glass-like material from which the elements and their amounts are easier to determine.
For trace element and contamination analyses, the closely related TXRF method (total reflection X-ray fluorescence) is a more appropriate option. Even though XRF can theoretically detect the emission of X-rays from almost all elements, in practice XRF spectrometers have limited ability to accurately measure elements with an atomic number smaller than 9.
Need an XRF analysis?
Measurlabs offers high-quality XRF testing services for a variety of industries and sample materials. If you have any questions about your sample or its suitability for the method, our experts are always happy to help. Do not hesitate to contact us to tell us more about your testing needs and to request a quote for testing services.
Suitable sample matrices
- Rocks, minerals, ores, sinters, and slags
- Sediment, soil, and slurry
- Cement, clinkers, lime, clays
- Glass and ceramics
- Catalysts
- Solid or powdered metals
- Crude oil and petroleum products
Ideal uses of XRF analysis
- Compositional analyses of earth samples in geology and environmental studies
- Soil surveys in geophysics
- Research of rocks (petrology)
- Examination of ores in mining
- Product development and quality control in metallurgy and the manufacturing of cement, ceramics and glass
- Determination of metal loading of supported metal catalysts
- Analyzing the composition of fossil fuels in the petroleum industry
- Checking the sulfur and lead content of gasoline
- Compositional analyses of jewelry
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Frequently asked questions
Small spots of the sample cannot be analyzed with XRF and thus the sample has to be relatively large. Samples typically have to weigh more than one gram and contain relatively large amounts of elements whose absorption and fluorescence effects are reasonably well understood. In order to perform a proper identification of the elements, compositionally similar standards for the sample material have to be available.
XRF can determine concentrations from 100 wt% (weight percentage) even to sub-ppm levels. However, the limit of detection for trace elements is typically on the order of a few ppm.
Theoretically, XRF can detect the emission of X-rays from an atom of virtually any element. However, in practice, most XRF spectrometers have limited ability to accurately measure elements with an atomic number less than 11.
XRF cannot detect the differences between different isotopes of the same element. Instead, isotope analysis is possible to perform with secondary ion mass spectrometry (SIMS) or thermal ionization mass spectrometry (TIMS). XRF also cannot distinguish ions of the same element with different valence states. Information about the ion composition can be obtained, for example, from wet chemical analysis or Mossbauer spectroscopy.
XRF is suitable for the analysis of relatively large samples weighing more than one gram. Geological and petrological samples, such as rocks, ores, minerals, and soil are especially well-suited for the analysis, but industrial products like ceramics and glass as well as petroleum products are also suitable.
When analyzing major elements, usually Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P can be determined. In the case of trace elements, usually Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, U, V, Y, Zr, and Zn are well-detected by XRF.
Especially, when studying rocks, ores, sediments, and minerals, the material should be ground down to a fine powder and homogenized. Sometimes, especially when analyzing trace elements, the analysis can be performed directly from the powder, but commonly the powdered sample has to be homogenized by melting it down with a chemical flux.
Measurlabs offers a variety of laboratory analyses for product developers and quality managers. We perform some of the analyses in our own lab, but mostly we outsource them to carefully selected partner laboratories. This way we can send each sample to the lab that is best suited for the purpose, and offer high-quality analyses with more than a thousand different methods to our clients.
When you contact us through our contact form or by email, one of our specialists will take ownership of your case and answer your query. You get an offer with all the necessary details about the analysis, and can send your samples to the indicated address. We will then take care of sending your samples to the correct laboratories and write a clear report on the results for you.
Samples are usually delivered to our laboratory via courier. Contact us for further details before sending samples.