Growing Applications of XRF Spectroscopy: In the Field, the Factory, and the Lab

As a fast, quasi-nondestructive analytical technique, X-ray fluorescence (XRF) spectroscopy is useful for a wide range of applications. To get a sense of the current breadth of XRF’s use and its potential growth in new areas, we asked a panel of experts to comment on the most important application areas for XRF, including the challenges involved and how XRF competes with other techniques.

Geological-related fields are a growing area for XRF application, noted Lora Brehm, a research scientist at Dow Chemical Company. “Geologists, geological engineers, lab technicians, drill geologists, mud loggers, and geochemists are all using XRF,” she said. Some examples include the use of down-hole and portable systems for mining and energy exploration and the use of XRF core scanners for chemostratigraphy studies. “Techniques like inductively coupled plasma–optical emission spectroscopy (ICP-OES) and atomic absorption do not lend themselves to field analysis as they require acid digestion of the sample, but XRF can be readily applied, especially with miniaturization of components.”

Martina Schmeling, an associate professor at Loyola University Chicago, agreed. “The trend is clearly to portability and ease of use in the field,” she said, adding that XRF may also find a place in hydraulic fracturing and gas exploration, given the robustness and ease of use of the method. “XRF has many advantages over the mass spectrometry (MS) methods-the major one being independent of carrier gases and other consumables,” she said. “It is important to keep in mind that there is an XRF spectrometer on Mars, but no ICP-MS.”

Ursula Fittschen, an assistant professor of analytical chemistry at Washington State University, looked more broadly at how XRF competes with other techniques, noting that usage depends on analyte levels and other factors. “Conventional XRF instrumentation is most attractive in all applications where parts-per-million levels are to be analyzed in refractory material,” she said. But for trace elemental analysis in the parts-per-billion range, she noted, ICP-OES is the workhorse, as long as sample material is not limited and digestion is straightforward. For limited samples, micro-analyzing tools like total reflection XRF or graphite furnace atomic absorption spectroscopy may be a better choice. “For detection at the parts-per-trillion level, one needs ICP-MS,” she added.

Several experts mentioned industrial applications for quality control, such as in iron and steel manufacturing. “The precision of steel products is quite high and wavelength-dispersive XRF is needed,” said Jun Kawai, a professor at Kyoto University. “There is one instrument that has 40-crystal spectrometers, making it possible to do quantitative analyses of 40 elements at once with a single XRF instrument.”

Industrial applications of XRF go beyond quality control, noted Don Broton, a principal scientist at CTLGroup. “Phase identification and standardless XRF enhance the capability of manufacturing plants to rapidly assess the use of alternative materials and formulations, as well as the by-products of their respective processes,” he said. “A green future will be enhanced by better characterization of these ‘wastes’ so more and better reuse is achieved.”

Future applications include the study of cultural heritage objects, as well as environmental, medical, and other technical fields, said Christina Streli, a professor at Vienna University of Technology. “The value of XRF will be seen wherever nondestructive investigation is valuable,” she said.

George Havrilla of Los Alamos National Laboratory agreed, adding that XRF is already proving its worth in cultural heritage studies. “The rapid growth of imaging works of art using micro XRF is allowing the discovery of overpainted pictures, giving new insights into the provenance of the art,” he said. “These techniques are also revealing how pigments degrade, leading us to understand that some colors we see in artwork today are not the same as they were when first painted by the artist.”

Havrilla also pointed to recent advances in optical tweezers, which use XRF to enable the mechanical manipulation of single cells, in turn enabling elemental imaging of cell contents in vivo. “This can lead us to new understandings of biological mechanisms,” he said.

Kenji Sakurai, a professor and group leader at the National Institute for Materials Science in Tsukuba, Japan, also sees developments in analyzing chemical states by XRF, including important work being done at synchrotrons using X-ray absorption fine structure (XAFS) and X-ray absorption near-edge structure (XANES) with XRF detection. “I believe that chemical state analysis by XRF will open new opportunities in science and many engineering fields.”

This article is an edited excerpt of “Analysis of the State of the Art: X-ray Fluorescence Spectroscopy.”

The article is part of a special group of six articles covering the state of the art of key techniques, also including, inductively coupled plasma–mass spectrometry (ICP-MS), laser-induced breakdown spectroscopy (LIBS), infrared (IR) spectroscopy, near-infrared (NIR) spectroscopy, and Raman spectroscopy.