To analyze the elements in a sample, scientists can use X-ray fluorescence (XRF), which can be performed with a benchtop or portable platform. Each option offers its own benefits and shortcomings.
The key benefit of portable XRF is in the name—portable. “Most portable systems can be run from a battery pack, making them flexible for use in virtually any location,” says David Fleming, professor of physics at Mount Allison University (Sackville, New Brunswick, Canada).
“The main difference between portable XRF and benchtop instruments is the power,” says Edenir Rodrigues Pereira-Filho, a chemist at the Federal University of São Carlos in Brazil. “Consequently, the sensitivity will be affected.”
The highest power and sensitivity come in benchtop XRF platforms. Still, Pereira-Filho notes that “portable XRF is suitable for fast alloy identification and to analyze a material for the presence of a specific element.” But that works only if enough of the element is in the sample. “If the concentration is around two to 10 percent or higher, it is possible to obtain results with relatively good accuracy,” he explains.
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Sample preparation is also easier with the portable approach. “The sample can be measured intact and nondestructively, so you will have the sample for future measurements as well,” says Aaron Specht, research fellow at the Harvard T.H. Chan School of Public Health (Boston, MA). Even if using a sample as is, “typical portable XRF systems have detection limits of parts per million or slightly less,” he says.
There are certain inconveniences associated with benchtop XRF, says Pereira-Filho. “Depending on the instrument, the sample must be cut in order to fit inside the sample chamber.”
To measure elements at lower levels, scientists need a benchtop XRF platform or other method, such as inductively coupled plasma-mass spectrometry (ICP-MS). For example, Pierre Masson, director of the Unit of Research and Service in Plant and Environmental Analyses at the Centre de Recherches INRA de Bordeaux (France), and his colleagues used lab-based XRF to analyze elements in plant samples, and found it faster than ICP-MS.
In some cases, though, portability really helps. “Portable XRF systems can be better for applications where factors such as cost, speed of results, and capability for on-site measurement are critical,” says Fleming.
Applications of portable instruments
The range of uses of portable XRF continues to expand. For Specht’s doctoral thesis, he adapted portable XRF to measure lead in human shinbones. “We were able to develop a calibration to accurately measure lead in people’s bones in three minutes by simply placing the portable XRF on their shin with our special equipment settings,” he says. “Since bones are a slow-growing organ, for adults one measure of bone lead can give us information on their lead exposure from the past 20 to 30 years.” Specht and his colleagues have used this method in studies of lead exposure in humans and wildlife.
Fleming’s research group is currently testing a portable XRF approach to assess levels of various elements in human toenail clippings, he says. “In the future, a portable XRF approach for this type of application could be especially useful, as it would return results to individuals quickly and at low cost.”
Specht works with lab-based methods of element detection, including ICP-MS, to find ways to make portable XRF as effective as possible. “Ultimately, portable XRF still has the limitations in detection limit, but with more powerful systems, it can be used in many more applications than previously thought.”