FT-IR Spectroscopy for Microplastic Classification

Microplastics (MPs) have emerged as one of the most pressing environmental challenges of the 21st century. Humans produce between 19–23 million metric tons of plastic end up in our sources of water (1). This number does not include the amount of plastic found in other environments, such as the desert or forest. Microplastics can be transported via air, originating from sources such as road traffic and ocean sprays (1). Natural weather occurrences such as wind and precipitation can transport microplastics to new environments as well (1).

Close-up side shot of hands shows microplastic waste contaminated with the seaside sand. Microplastics are contaminated in the sea. Concept of water pollution and global warming. | Image Credit: © Pcess609 - stock.adobe.com

Microplastics have damaging effects on the environment. For example, if microplastics find their way into the soil of desert landscapes, they can damage the growth of the flora and fauna in that environment (2). This makes it crucial for environmental scientists to find, classify, and detect microplastics in the environment to safeguard the environment.

Spectroscopy techniques can play a role in this endeavor. A recent review article published in Infrared Physics & Technology led by Collins Nan Andoh and other researchers from several universities in Ghana explored how Fourier transform infrared (FT-IR) spectroscopy can help address this problem (3). The researchers demonstrate in their article that FT-IR spectroscopy has great utility in this field.

Microplastics, defined as plastic particles smaller than 5 millimeters, originate from a variety of sources, including degraded larger plastics and synthetic textiles (2,3). These tiny pollutants infiltrate diverse environmental matrices, such as soil, water, and air, posing significant risks to ecosystems and human health (1–3).

FT-IR spectroscopy uses the interaction of infrared (IR) light with materials to identify their chemical composition, making it particularly effective for characterizing the polymers found in microplastics. According to the authors, FT-IR stands out because of its ability to detect functional groups, determine particle size and shape, and track pollution sources (3). However, like all techniques, FT-IR has its challenges, including its limitations in analyzing mixtures of plastics, detecting very small microplastics, and the need for specialized expertise and well-maintained equipment (3).

The review article explored the pros and cons of using FT-IR spectroscopy by comparing it to other spectroscopic techniques. Techniques such as Raman spectroscopy and pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) each offer unique advantages. For example, Raman spectroscopy excels in detecting smaller particles but can struggle with fluorescence interference (3). On the other hand, FT-IR provides a broader application range and is often used in conjunction with other methods to overcome its limitations, enhancing the accuracy and depth of microplastic analysis (3).

The review emphasizes the importance of advancing FT-IR technology to address its current shortcomings. Enhancements in speed, accuracy, and sensitivity—especially for detecting low concentrations of microplastics—are crucial (3). FT-IR methodologies are also continuing to be worked on and improved, usually in collaboration with analytical chemists, researchers, and engineers.

One of the key insights from the review article is FT-IR's capability to contribute to understanding the environmental interactions and fate of microplastics. By providing detailed information on chemical composition, particle morphology, and pollution pathways, FT-IR spectroscopy plays a vital role in formulating targeted strategies to mitigate the impact of microplastics (3). This is particularly important as policymakers and environmental agencies worldwide grapple with the growing microplastic crisis (3).

Although FT-IR spectroscopy has its limitations, it offers numerous advantages for microplastic detection. This review article highlighted how FT-IR spectroscopy is set to continue to be used in this space, especially in conjunction with other analytical methods (3). As the field of microplastic research continues to evolve, FT-IR is set to be one of the top techniques in microplastic detection.

References

1. Wetzel, W. Measuring Microplastics in Remote and Pristine Environments. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/measuring-microplastics-in-remote-and-pristine-environments (accessed 2024-12-19).
2. Wetzel, W. Microplastics in the Desert: A Growing Concern in Phoenix Soils. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/microplastics-in-the-desert-a-growing-concern-in-phoenix-soils (accessed 2024-12-19).
3. Andoh, C. N.; Attiogbe, F.; Ackerson, N. O. B.; Antwi, M.; Adu-Boahen, K. Fourier Transform Infrared Spectroscopy: An analytical technique for microplastic identification and quantification. Infra. Phys. Technol. 2024, 136, 105070. DOI: 10.1016/j.infrared.2023.105070