Air pollution is a huge public health hazard, and pollution levels and constituent parts are routinely monitored. Sample preparation methods required by commonly used analytical methods are destructive, expensive and time-consuming and carry contamination risks. Professor Laura Borgese and Dr Fabjola Bilo of the University of Brescia, Italy, have developed Smart Store® – a new portable, non-destructive system that enables researchers to prepare samples in a rapid, sustainable, and economical manner.
It is common knowledge that human activities have caused pollution in the environment, particularly in urban areas. Particulate matter is a prominent pollutant in the air which can cause, for example, respiratory and cardiovascular diseases. It can also accumulate in the food chain, bringing both health and ecological risks. To safeguard public health, scientists routinely monitor the concentration and size of particulate matter; they also determine its chemical composition to help reveal the specific origins of each pollutant.
The processes for carrying out this important work are well established but can be expensive and time-consuming. Professor Laura Borgese and Dr Fabjola Bilo, of the University of Brescia, Italy, have developed the Smart Store® system to address these problems, and their spin-off company, Smart Solutions, is ensuring that this useful technology is readily available to scientists.
Currently, air-quality monitoring is carried out by filtering particulate matter from the air at monitoring stations at various locations, and then sending the samples to an analytical laboratory. Typical analytical practice is then to dissolve the filter membrane in an acidic solution using microwaves, and then identify the elements in the resulting sample using atomic absorption spectroscopy (the chemical elements are identified based on the absorption of light by atoms in the gas state) or inductively coupled plasma spectroscopy (plasma is used to induce the emission of light by chemical elements).
Common elements detected in particulate matter are aluminium, calcium, iron, magnesium, potassium, and silicon, usually present in their oxidised states. Other potentially toxic elements, such as the heavy metals cadmium, arsenic, chromium, lead, and nickel, may also be present.
These elemental analysis methods involve destruction of the sample, which may be expensive, and they are time-consuming. The use of acid to digest the samples is not environmentally friendly and may preclude the detection of trace elements. There is also a risk that samples could be lost or contaminated during handling or transport.
Smart Store® is used to prepare samples that are then analysed using TXRF spectrometers. This process involves exposing the atoms in the particulate matter sample to X-rays. This results in an electron being ejected from an inner shell of the atom and the vacancy becomes filled with an electron from an outer shell of the atom. This movement of the electron to the lower energy inner shell releases a fluorescent X-ray, the energy of which depends on the chemical element being tested. If the energy of the applied X-ray is insufficient to dislodge an inner shell electron, then there is no fluorescence.
Total reflection X-ray fluorescence is a variation of X-ray fluorescence, in which the geometry of the instrumentation is optimised so that chemical elements can be detected at lower levels.
Normally, when X-rays are applied to a sample, some of the X-rays are reflected and some are refracted through the sample. However, there is a minimum glancing angle for the applied X-rays below which all of the X-rays are reflected and none are refracted, which maximises the intensity of the signal received by the detector. Furthermore, if the detector is placed close to the sample along the angle of reflection, then this too will enhance the fluorescence signal.
This particular X-ray fluorescence method has the advantage of being able to determine the chemical composition of particulate matter without the need to dissolve samples in acids, or indeed for any destruction of the sample. Furthermore, this technique can be used while the particulate matter is on the filter, which minimises sample handling and the associated risks of sample contamination and material loss.
The Smart Store® instrument includes an automatic device for standardising the sample-handling procedure. The device fixes the material to be tested on a filter membrane between two sheets of adhesive polymers and cuts it into a disc 30mm in diameter. The sample can be stored for re-testing and this approach does not preclude the option of destructive testing later.
Suitable filter types include acetate cellulose, polytetrafluoroethylene (PTFE), polycarbonate, borosilicate, and quartz. PTFE filters are usually preferred since they have lower impurities than quartz and a smoother surface.
This X-ray fluorescence method does not require the sample to be dissolved or suspended in a matrix (a medium for handling the sample). It was demonstrated that it possible to quantitatively measure the amounts of each element in a particulate matter sample with linear calibration, i.e., the intensity of the fluorescence is proportional to the concentration of the chemical element.
Effective, efficient and sustainable
The SMART STORE® system has been created ‘by scientists for scientists’. This means that it is straightforward for the general scientist to use, as well as serving the identified needs of a wider community of X-ray fluorescence users.
A significant benefit is that Smart Store® is portable, which means that the user can prepare their sample at the air monitoring station. This eliminates the need to transport the filters to an analytical ‘wet’ lab and the associated risks to the sample. The user requires only a few micrograms of particulate matter collected on the filter and the TXRF measurements can be performed in less than ten minutes.
The Smart Store® has a dedicated and customised calibration module. This assists scientists by implementing appropriate algorithms to generate the calibration curves for known amounts of chemical elements made using reference materials, in a dedicated section of the instrument software, which is accessible through a web platform.
The system also has a classification app for android, and online software to record and share data and analytical information. Each sample corresponds to a datasheet and a unique QR code for the correspondence between physical material and digital archive. All information is stored in the cloud, available for registered users.
Professor Borgese and Dr Bilo have found that their method produces results that are comparable to those afforded by atomic absorption spectroscopy and inductively coupled plasma spectroscopy. They predict that it will enable the detection of trace elements which may not have been observed using other methods. This method will open up new analytical opportunities due to the possibility of sample screening, significantly reducing the environmental impact of laboratory analysis.
Analytical methods developed using SMART STORE®, coupled with TXRF, have already been shown to accurately quantify low levels of lead, and Professor Borgese aims to demonstrate this accuracy for other important chemical elements in the environment such as cadmium, arsenic, nickel and mercury.
The researchers are investigating how this new technology could be used to assess the presence of toxic elements in soil, water, and waste. They have a particular interest in biomonitoring – the assessment of pollutants in organisms and in ecosystems. X-ray fluorescence has already been used to assess particulate matter on leaves from trees, and Professor Borgese considers that SMART STORE® technology may be used to assess the quality and safety of both food, cosmetics, and the emerging field of pharma.
The research team are also investigating the use of other non-destructive analytical methods for assessing pollutants.
- Borgese, L, Zacco, A, Bontempi, E, Depero, L, (2014). A new method for sample preparation and chemical analysis of atmospheric aerosols. DUST2014 – 1st International Conference on Atmospheric Dust, Conference Article.
- Borgese, L, Bilo, F, Zacco, A, et al, (2020). The assessment of a method for measurements and lead quantification in air particulate matter using total reflection X-ray fluorescence spectrometers. Spectrochimica Acta Part B, [online] Volume 167, Article 105840. DOI.org./10/1016/j.sab.2020.105840 [Accessed 06 Jul. 2021].
- Cirelli, P, Bilo, F, Tsuji, K, et al, (2021). Calibration methods for the analysis of Pb-loaded air filters by total reflection X-ray fluorescence spectrometers. Spectrochimica Acta Part B, under revision.
- Bacon, J, Butler, O, Cairns, W, et al, (2021). Atomic Spectrometry Update – a review of advances in environmental analysis. J Anal At Spectrom. [online] Volume 36, 10–55. DOI:10.1039/D0JA90074E [Accessed 06 Jul. 2021].
The development of sample preparation methods for direct analysis, dedicated to environmental monitoring and pollution assessment, drug purity, food and cosmetic safety.
This work was supported by Regione Lombardia Bando Innodriver S3 – edizione 2019, Misura B (CUP E88I20000060007).
- Annalisa Zacco, Elza Bontempi and Laura E Depero, Chemistry for Technologies (Chem4Tech) Laboratory, Department of Mechanical and Industrial Engineering, University of Brescia
- Andrea Buccelli, Eng, AMD Engineering S.r.l
- Diego Moscardi, Webbergate S.r.l
Laura Borgese PhD is Associate Professor in the Department of Mechanical and Industrial Engineering, University of Brescia, and CEO of Smart Solutions.
Fabjola Bilo PhD is researcher of the National Interuniversity Consortium of Materials Science and Technology, member of the board of Smart Solutions, and has a Manager for Excellence masters degree.
Smart Solutions s.r.l. – Via Corfù 106 – 25124 Brescia, Italy