Fast and Simple Material Identification of Plastic Debris Using FTIR Spectrometry

Significance of the Topic

Global plastic production now exceeds 400 million tons of waste annually, much of which contaminates natural ecosystems including shorelines. Reliable, rapid analytical methods for identifying polymer types in environmental debris are essential to understand pollution sources, degradation pathways and to inform mitigation strategies. Fourier transform infrared (FTIR) spectroscopy, particularly with attenuated total reflectance (ATR), offers a cost-effective approach to characterize diverse plastics, from macro-debris to microplastics.

Objectives and Study Overview

This application note describes a streamlined workflow for polymer-type identification of weathered plastic fragments collected from Mordialloc Beach in Victoria, Australia. The primary aims were to demonstrate how the Agilent Cary 630 FTIR spectrometer with ATR can be used to:

• Prepare beach-collected samples for spectral analysis
• Generate a user-defined polymer library from standard reference materials
• Acquire and compare ATR spectra using a similarity-based search
• Rapidly report qualitative identifications with confidence metrics

Methodology and Instrumentation

Sample Collection and Preparation:
Plastic fragments exhibiting visible environmental degradation were randomly collected; nine distinct samples were selected. Hard plastics were sectioned into ~2 mm slices to maximize contact with the ATR crystal.
Instrumentation and Software:
An Agilent Cary 630 FTIR spectrometer fitted with a diamond ATR module was controlled via Agilent MicroLab software. The picture-driven interface guides each analytical step, reducing user training and error.
Operating Parameters:

• Spectral range: 4000–650 cm⁻¹
• Resolution: 4 cm⁻¹
• Background scans: 64; sample scans: 64
• Library search method: Similarity algorithm against a user-generated polymers library
• Confidence thresholds: green >0.95, yellow 0.90–0.95, red <0.90

Main Results and Discussion

Of the nine analyzed samples, eight were identified as polypropylene and one as high-density polyethylene. Hit quality indices (HQI) ranged from 0.9465 to 0.9940 for polypropylene and 0.9711 for polyethylene. Color-coded results displayed directly on the instrument screen facilitated instant assessment of identification confidence. The workflow demonstrated consistent, high-quality matches even for weathered debris, illustrating the robustness of the ATR-FTIR approach and the ease of maintaining a custom spectral library within MicroLab.

Benefits and Practical Applications

This method provides multiple advantages for environmental researchers and quality-control laboratories:

• Minimal sample preparation and rapid analysis for high throughput
• Intuitive, image-driven software reduces operator variability
• Customizable libraries allow targeted identification of relevant polymers
• On-site or laboratory use supports both field campaigns and routine monitoring

Future Trends and Opportunities

Advances in portable and imaging-based infrared instruments will further expand microplastics research capabilities. Emerging technologies include laser direct infrared (LDIR) chemical imaging for submicron particles, handheld FTIR for in-field screening and compact benchtop units for decentralized testing. Integration of artificial intelligence in spectral matching, automated library updates, and coupling with microscopy and mass-based quantification will enhance real-time environmental monitoring and pollution source tracing.

Conclusions

The Agilent Cary 630 FTIR spectrometer with ATR and MicroLab software offers a fast, simple, and reliable solution for polymer identification of plastic debris. The turnkey workflow—from sample preparation through color-coded reporting—supports rapid decision-making and contributes to improved understanding of plastic pollution in natural environments.

References

1. United Nations Environment Program, Our Planet is Choking on Plastic, accessed April 2023.
2. Andrady A. L., Weathering and Fragmentation of Plastic Debris in the Ocean Environment, Marine Pollution Bulletin, 2022, 180:113761.
3. Lavers J. L.; Rivers-Auty J.; Bond A. L., Plastic Debris Increases Circadian Temperature Extremes in Beach Sediments, Journal of Hazardous Materials, 2021, 416:126140.