Accurate Microplastic Analysis of Bottled Drinking Water

Importance of the topic

Microplastics, particles between 1 µm and 5 mm, have become pervasive due to plastic pollution and pose potential health risks via ingestion. Bottled water consumption is rising globally, making reliable methods to detect and quantify microplastics in drinking water crucial for public health and regulatory monitoring.

Objectives and study overview

This study employed the Agilent 8700 LDIR Chemical Imaging System to accurately identify and quantify microplastics in two commercial bottled water brands. Additionally, the Agilent Cary 630 FTIR spectrometer with a diamond ATR module was used to trace the source of contamination by characterizing the polymer composition of bottle and cap materials.

Methodology and instrumentation

• Sample preparation: Two 600 mL bottled water samples were filtered through 0.8 µm polyester (PETG) gold-coated membranes using a small-pore glass frit vacuum system to collect particles. Filters were rinsed, mounted, and secured for analysis.
• LDIR analysis: The Agilent 8700 LDIR system, controlled by Clarity software, performed automated Particle Analysis using scan and sweep modes to locate particles via IR imaging at 1442 cm⁻¹ and acquire full mid-infrared spectra for library matching.
• ATR-FTIR confirmation: Bottle and cap fragments (~5 mm) from each brand were directly measured with the Agilent Cary 630 FTIR spectrometer using a diamond ATR accessory. Spectra were compared to a user-generated polymer library for identification.

Main results and discussion

Brand A yielded 98 detected particles, with four confirmed microplastics (75% polyethylene, 25% polyethylene terephthalate) sized 20–100 µm. Brand B showed 1 112 particles, of which 33 were microplastics (69% PE, 9% PET, 24% PA) ranging from 20 µm to 703 µm. Non-plastic particles included cellulosic and natural polyamides. ATR-FTIR analysis identified the bottles as PET and caps as high-density PE, suggesting PE contamination likely originated from bottle handling.

Benefits and practical applications

• The on-filter LDIR method minimizes sample handling, reducing contamination risk and increasing throughput.
• Automated Particle Analysis provides rapid quantification and chemical classification of microplastics in environmental and QA/QC workflows.
• FTIR polymer identification offers a straightforward approach to trace contamination sources, with intuitive software reducing training requirements and user error.

Future trends and potential applications

Advancements will focus on expanding spectral libraries for diverse polymers, integrating automated microplastic analysis into large-scale environmental monitoring, and standardizing protocols for regulatory compliance. Combining LDIR imaging with advanced data analytics may further enhance throughput and detection sensitivity.

Conclusion

The combined application of Agilent 8700 LDIR imaging and Cary 630 FTIR spectroscopy delivers a robust workflow for detecting, quantifying, and attributing the source of microplastics in bottled water. This approach supports high-throughput analysis with high confidence, benefiting environmental studies, quality control laboratories, and public health assessments.

Used instrumentation

• Agilent 8700 Laser Direct Infrared (LDIR) Chemical Imaging System
• Agilent Cary 630 FTIR Spectrometer with diamond ATR module
• Sterlitech polyester (PETG) gold-coated membrane filters, 0.8 µm

Reference

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