Sample Preparation Method and FTIR Analysis Method for Microplastics Sampled from Rivers

Sample Preparation and FTIR Analysis of River Microplastics

Significance of the Topic

Microplastics are pervasive contaminants in aquatic environments, posing risks to ecosystems and human health. Reliable monitoring and characterization of these particles are essential for understanding their distribution, sources, and degradation pathways. Improved sample preparation and analytical methods enhance data quality and support global efforts to standardize microplastics surveys.

Objectives and Overview

This study outlines a workflow for sampling microplastics from rivers, preparing them for analysis, and characterizing their chemical degradation using Fourier transform infrared (FTIR) spectroscopy. The approach employs a portable sampling device and a standardized laboratory protocol to remove contaminants and isolate plastic particles, followed by spectral evaluation to identify polymer type and oxidative damage.

Methodology and Instrumentation

The procedure consists of:

1. Field sampling with a buoyant Albatross microplastic collector submerged for 3 minutes to capture particles from river water.
2. Sieving the collected material through 2 mm and 0.1 mm meshes to separate target particles.
3. Chemical treatment using 30 % hydrogen peroxide at 60 °C for 3 days to digest organic contaminants.
4. Gravity separation with 5.3 M sodium iodide solution to concentrate microplastics in the supernatant.
5. Air-drying the isolated particles before FTIR analysis.

Instrumentation

The analysis was performed on a Shimadzu IRSpirit FTIR spectrophotometer equipped with a QATR-S diamond single-reflection ATR accessory, using:

• Spectral resolution: 4 cm⁻¹
• Number of scans: 45 accumulations
• Wavenumber range: 4000–600 cm⁻¹
• Detector: DLATGS
• Apodization: SqrTriangle
• Software: Plastic Analyzer method package with a UV-degraded plastics library

Key Results and Discussion

FTIR spectra of the isolated particles matched polyethylene (PE) degraded by 550 hours of UV exposure. Characteristic absorption bands at ~3400 cm⁻¹ (O–H stretching) and ~1750 cm⁻¹ (C=O stretching) indicated oxidative alteration. An additional feature near 1050 cm⁻¹ suggested silicate residue, highlighting the importance of contaminant removal steps. The use of a dedicated UV-damaged plastics library enabled rapid and reliable identification of polymer type and degradation state.

Practical Implications and Applications

The described workflow offers a straightforward and reproducible approach for environmental laboratories to monitor microplastic pollution. Key benefits include:

• Minimized sample contamination through controlled chemical digestion and density separation.
• Rapid polymer identification and degradation assessment without extensive operator expertise.
• Scalability for routine monitoring in rivers, estuaries, and coastal waters.

Future Trends and Opportunities

Advancements may include automated sampling platforms, integration of complementary techniques (e.g., Raman spectroscopy), expansion of spectral libraries for diverse polymer types, and development of in-field ATR devices. Machine learning could further enhance spectral interpretation and classification of complex environmental samples.

Conclusion

This study demonstrates a robust method for sampling, preparing, and analyzing riverine microplastics using FTIR spectroscopy. The workflow achieves high reliability in polymer identification and degradation assessment, supporting environmental monitoring and comparative studies across different regions.