Newswise — Researchers at the Technical University of Munich (TUM) have devised an automated analysis technique to measure the concentrations of microplastics in the environment, including drinking water and food. Microplastics, which are minuscule particles with diameters smaller than 5 millimeters, are pervasive in our surroundings and can accumulate contaminants and toxins. Dr. Natalia Ivleva, from the Chair of Analytical Chemistry and Water Chemistry at TUM, emphasizes the urgent need for accurate analytical methods to determine the size, concentration, and composition of these particles. Together with her team, she has successfully developed a novel process to address this crucial issue.
Detecting microplastic particles posed significant challenges for the researchers, and they had to surmount several hurdles. The primary obstacle was the issue of low concentrations. In bodies of water such as rivers, a substantial volume of suspended solids and fine sand exists, with plastic particles comprising less than 1 percent of the total. Consequently, isolating these microplastic particles became the first crucial step before accurately determining their concentrations and chemical composition.
Previous methods relied on analyzing the residues released when samples were subjected to heat. However, this approach lacked the capability to ascertain the precise number, size, and shape of the plastic particles, rendering it insufficient for the researchers' purposes. To overcome these limitations, the team developed a new and improved process for identifying and quantifying microplastics
Plastics can be identified through light scattering
According to Dr. Ivleva, our approach sets itself apart from others as it is particle-based, involving the direct analysis of particles rather than their destruction. To achieve this, we employ Raman microspectroscopy, a method that utilizes a monochromatic laser to illuminate a sample and then detects the light scattered by the molecules. By comparing the scattered light with the laser source, we gain valuable information about the substance being studied.
When examining plastic particles with a diameter larger than 1 µm (micrometer), we first isolate them from the aqueous solution through filtration. Subsequently, these particles are detected under a microscope and subjected to laser light illumination. As plastics like polyethylene, polystyrene, and polyvinyl chloride display distinctive ways of scattering photons, each material generates signals akin to a unique fingerprint. This characteristic behavior allows us to differentiate between different types of plastics and study them in a precise and targeted manner.
Automation instead of manual measurements
The development of the tracing process was a long and laborious endeavor, with the chemist recalling the initial days of manual measurements, which took months to investigate just a few thousand particles. However, over time, the team has made significant progress and successfully automated the detection of microplastics. What used to take weeks to analyze can now be accomplished within a matter of hours.
Though the process still involves filtering out the tiny particles from the aqueous solution and placing the filter under the Raman microspectroscope, the team's software handles all subsequent steps. Using a light microscope, the software localizes the plastic particles, takes photographs, measures them, and distinguishes particles from fibers. These data are then utilized by the software to compute the number of particles and fibers and identify the image sections necessary for statistically significant results in the subsequent Raman spectroscopy.
During the next stage, the sample is exposed to the laser, and the scattering is detected and analyzed. This provides a rapid and reliable analysis of various attributes, including the number, size, shape, and composition of the microplastics.
The team's hard work has culminated in the creation of the open-source TUM-Particle Typer 2 software, which is now available to researchers worldwide. This software represents a significant advancement in the field, enabling more efficient and accessible analysis of microplastics for researchers around the globe.
Nanoplastics require special detection processes
To explore nanoparticles with diameters less than 1 µm, Dr. Ivleva's team has undertaken a modified approach. According to the researcher, these tiny nanoparticles pose challenges as they are difficult, if not impossible, to distinguish using a light microscope. To detect them, a two-step process is implemented involving size fractionation and subsequent identification.
To achieve this, the team employs a field flow fractionation (FFF) system. This system creates a water flow that captures the nanoparticles and separates them based on their size by transporting them at varying speeds. By utilizing a specially developed device in conjunction with Raman spectroscopy, the team can chemically characterize different types of nanoplastics.
Dr. Ivleva emphasizes that these novel analytical methods enable swift and precise investigations of the concentration, size, and composition of both micro- and nanoplastics. Consequently, this advancement opens up avenues for studying the impact of these particles on the environment and human health with greater accuracy and efficiency.
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