Portable XRF devices put this technology in the field for art, environmental studies, and more
Two scientists from the University of California at Los Angeles (UCLA) explored the chemical composition of Chinese blue-and-white porcelain.1 The researchers focused on porcelain from Jingdezhen and Zhangzhou, which produced large amounts of this product in the late 16th to early 17th centuries. As the investigators pointed out: “scientific analysis has often relied on sophisticated laboratory-based instrumentation, a methodology that can be used neither for large sets of archaeological sherds nor in the field.” So, they turned to field-worthy technology, including portable X-ray fluorescence (pXRF).
The researchers analyzed pieces of porcelain found in Indonesia and the Philippines, and the results showed that levels of elements, especially zirconium and thorium, could reveal where the piece was produced—in this work, Jingdezhen or Zhangzhou. They noted: “The composition of the cobalt-based blue pigment was also easily identified with pXRF, highlighting the Fe-poor and Mn-rich compositional pattern in accordance with the local asbolite ores used during this time period.”
Using pXRF makes for fast and efficient chemical analysis of items in the field. Scientists can compare devices from a range of suppliers, including Bruker (Billerica, MA), Olympus (Tokyo, Japan), Oxford Instruments (Abingdon, U.K.), and Thermo Fisher Scientific (Waltham, MA). When asked about some of the key applications of pXRF, Kim Russell, market and sales development at Bruker Nano Analytics, lists mineral exploration, consumer-product screening, scrap-metal sorting, alloy-grade identification, and more. “For instance, a handheld XRF configured in a tripod or extension pole is ideal for the analysis of pigments in a fresco or painting, as well as for the mosaic pattern in the middle of a floor you’re not permitted to stand on,” Russell says.
Portable X-ray fluorescence (pXRF) can be used to analyze plastic pieces found on beaches.XRF is a form of spectrometry that analyzes the elements in the sample. Energy from the device—radiation—causes atoms in a sample to be excited and emit X-ray photons of characteristic energies related to the element. These energies are essentially an elemental fingerprint that can be used to identify and quantify the elements that make up a sample. In addition, this technique does not destroy the sample. A benchtop XRF platform provides lower detection limits, but pXRF is “good for 5 parts per million for many metals,” says marine chemist Andrew Turner of Plymouth University (U.K.). “People think the main drawback is limited detection, but you need to weigh that against the convenience.” Combine the convenience and the detection capabilities, and pXRF can be used in many ways.
Measuring microplastics
Some of the most varied possibilities for using pXRF involve environmental science, such as analyzing microplastics found on beaches. Writing on the U.S. National Oceanic and Atmospheric Administration (NOAA) website, research scientist Stefanie Whitemire of the Baruch Institute of Coastal Ecology & Forest Science at Clemson University in South Carolina explained, “Microplastics are plastic pieces measuring less than five millimeters in size, and in recent decades there have been many studies that indicate a strong presence of this type of debris in marine and coastal environments.” As Whitemire points out: “Unfortunately, the presence of microplastics in the marine environment poses risks to wildlife.”
Turner used pXRF to explore beach microplastics.2 “On some beaches after a storm, microplastic dominates the strandline of a beach,” he says. To study the elements in a plastic, it is usually dissolved in a strong acid at high temperature, which creates waste, and some elements evaporate. Turner wanted to develop a method that can be used easily in the field. From this work, Turner found more lead and cadmium in the plastics than he had expected, because these substances are now banned. “You can attribute finding so much of those elements to the fact that some of the plastic in the ocean is 30 or 40 years old.” Turner has also used pXRF to analyze elements in seaweed, bird feathers, boat paints, and more.
Measuring metals
Many other environmental applications of pXRF can be found, limited only by a scientist’s imagination. A team of scientists from Australia applied this technology to sites contaminated by metals.3 They wanted to know the value of increased environmental sampling that could come from using portable technology. They also wondered if this technology could lower the cost of environmental decision-making. To find out, they applied pXRF to soil samples at five sites with metal contamination. For comparison, the scientists performed in situ pXRF measurements and inductively coupled plasma/mass spectrometry (ICP/MS). The results showed that more sampling reduced uncertainty. In addition, the team noted: “Real-time pXRF data enabled efficient, on-site decision making for further judgmental sampling, without the need to return to the site.” Plus, pXRF cost less than taking samples to a lab for ICP/MS analysis. They also noted that “a probabilistic site assessment approach was applied to demonstrate the advantages of integrating estimated measurement uncertainties into site reporting.”
In Korea, two scientists applied pXRF to soil samples from abandoned mining areas. They studied the soil concentrations to find areas with higher concentrations of toxic elements than surrounding areas, which they called hot spots. They did note that relatively low accuracy of the pXRF data required transformation based on ICP/MS results. They concluded: “The method implemented in this case study may be utilized in the field for the assessment of statistically significant soil contamination and the identification of areas for which an additional survey is required.”
Metal pieces or slivers found in food products can also be measured. “Plant managers need to identify these foreign bodies and quickly determine their source in order to take corrective action on the manufacturing floor,” Russell explains. “To be most effective, all production floor alloys are identified and catalogued with the handheld XRF.” With every possible culprit catalogued, says Russell, “a matching library can be set up on the handheld XRF to identify the source of the metal contaminant found in the food.”
Purchase the right performance
When shopping for a pXRF product, Russell encourages customers to consider several basic features: range of detectable elements, range of detection limits, and available preloaded calibrations. “Then, you need to consider usage features—lightweight, rugged, safe, easy-to-read display, data collection setups, data transfer, and available accessories,” she says. “You also need to look for features that deliver answers in the form you need: pass/fail, yes/no, alloy ID, precious metal assessment, elemental composition, and/or spectra.”
Depending on the application, the software also makes a big difference. “If the handheld is not used for standard point-and-shoot analyses, you also need to consider the availability of usergenerated quantitative analysis/correlation software and advanced/flexible qualitative analysis software,” Russell notes.
Turner points out that a pXRF is simple to use and includes safety mechanisms. Nonetheless, when using a pXRF, scientists must be careful. “A portable XRF is a mobile radiation source,” he says, “and you have to be trained to use it.”
Taking an instrument to a sample’s natural site allows more opportunities to study a larger number of samples, to do so quickly, and to be able to review the data later. The accuracy of this technology makes it a powerful tool to take to the field for chemical analysis.
References
- Fischer, C; Hsieh, E. Export Chinese blue-and-white porcelain: compositional analysis and sourcing using non-invasive portable XRF and reflectance spectroscopy. J. Archaeol. Sci. 2017, 80, 14–26.
- Turner, A. In situ elemental characterisation of marine microplastics by portable XRF. Mar. Pollut. Bull. 2017; doi: 10.1016/j.marpolbul.2017.07.045. [Epub ahead of print]
- Rouillon, M.; Taylor, M.P. et al. Reducing risk and increasing confidence of decision making at a lower cost: in-situ pXRF assessment of metal-contaminated sites. Environ. Pollut. 2017, 229, 780–9.
- Kim, S.M. and Choi, Y. Assessing statistically significant heavy-metal concentrations in abandoned mine areas via hot spot analysis of portable XRF data. Int. J. Environ. Res. Public Health 2017; doi:10.3390/ijerph14060654.
Mike May is a freelance writer and editor living in Texas. He can be reached at mike@techtypercom