Analyzing Colored Microplastics with the Agilent 8700 Laser Direct Infrared (LDIR) Chemical Imaging System

Importance of the Topic

Microplastics are pervasive environmental contaminants that can accumulate dyes and pigments, complicating their identification by conventional spectroscopic methods. Colored microplastics may interfere with Raman-based analysis due to fluorescence and overlapping spectral features, leading to misclassification. Reliable detection and characterization of colored particles are essential to assess their distribution, ecological impact, and to inform remediation strategies.

Objectives and Overview of the Study

This application note evaluates the performance of the Agilent 8700 Laser Direct Infrared (LDIR) Chemical Imaging System for automated identification of colored polyethylene terephthalate (PET) microplastics. The primary goals are:

• To determine whether dyes or pigments in brown, white and blue PET microplastics affect LDIR-based detection and identification.
• To assess the accuracy, confidence levels and throughput of a fully automated particle analysis workflow.

Methodology and Instrumentation

Samples of brown, white and cobalt blue 100 mL PET bottles were ground into fine powder, suspended in ethanol, and deposited on a low-e infrared reflective glass slide. After drying, the slide underwent an automated imaging and analysis sequence with the Agilent 8700 LDIR system equipped with Clarity software. Key steps included:

• Initial rapid infrared scan at 1,442 cm⁻¹ to locate particles based on C–H absorbance.
• Automated high-resolution spectral acquisition for each detected particle.
• Library matching using the Microplastics Starter 2.0 spectral library, with hit quality index thresholds (low: 0.65–0.75; medium: 0.75–0.80; high: 0.80–0.99).

Main Results and Discussion

More than 150 particles were detected per scanned area for each color. Identification rates of PET microplastics exceeded 96% for all colors, with high-confidence matches for 76.6% (brown), 89.7% (white) and 84.9% (blue) of particles. Spectral overlays showed nearly identical absorption profiles for all colored PET samples, indicating that colorants do not generate additional infrared peaks. High-magnification visible images further supported robust particle classification.

Benefits and Practical Applications

Implementing the Agilent 8700 LDIR system offers:

• Automated, high-throughput identification unaffected by particle color.
• Elimination of time-consuming method optimization or specialized dye libraries.
• Comprehensive particle statistics including size, count and composition.

Future Trends and Applications

Advancements may include expanding spectral libraries to encompass a broader range of polymers and additives, integrating LDIR with complementing techniques for complex matrices, and deploying portable imaging units for field monitoring of microplastics in diverse environmental samples.

Conclusion

The Agilent 8700 LDIR Chemical Imaging System reliably identifies colored PET microplastics with high confidence and throughput. Its automated workflow circumvents challenges posed by dyes and pigments in Raman analysis, streamlining routine microplastics characterization in environmental and industrial applications.

Reference

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