Accurate Microplastic Characterization in Infant Formula

Importance of the Topic

Microplastics are pervasive contaminants found in water, food and consumer products. Infants may be unintentionally exposed through formula, which contains complex matrices of fats, proteins, minerals and carbohydrates. Accurate characterization of microplastics in infant nutrition is critical to assess exposure risks and ensure quality control.

Objectives and Study Overview

This application note describes a workflow for isolating and quantifying microplastics in two commercial infant formula brands using the Agilent 8700 Laser Direct Infrared (LDIR) Chemical Imaging System. The goals were to develop an efficient extraction protocol, validate reagent cleanliness, and demonstrate rapid, automated microplastic identification.

Methodology and Instrumentation

• Sample Preparation: 5 g of formula dissolved in saturated NaCl, centrifuged to yield a cream (upper) and aqueous (lower) layer.
• Digestion: Upper layer treated with 0.1 M NaOH at 50–60 °C, filtered through 14 µm polycarbonate, rinsed into tubes with ethanol.
• Filtration: Both layers filtered onto 25 mm PETG gold-coated membranes (0.8 µm pore) for direct LDIR analysis.
• Quality Control: Milli-Q water, NaCl solution and EtOH screened by LDIR and filtered repeatedly to remove background microplastics before use.
• Instrumentation: Agilent 8700 LDIR with Clarity software Particle Analysis workflow. Scan mode locates particles at 1 442 cm⁻¹; sweep mode acquires full mid-IR spectra matched to the Microplastics Starter 2.0 library. Hit Quality Index thresholds: low (0.65–0.75), medium (0.75–0.85), high (0.85–0.99).

Main Results and Discussion

• Reagent QC: Ultra-pure water initially contained 6 microplastics (PE, PU) out of 184 particles; sat. NaCl showed 81 microplastics across 392 particles. Both were cleared by repeated filtration.
• Infant Formula Brand A: 4 472 particles detected; 97 true microplastics (63 upper layer, 34 lower layer), mainly PE and PP sized 20–100 µm. Many non-plastics were natural polyamides from residual proteins.
• Infant Formula Brand B: 1 078 particles detected; 22 microplastics (9 upper, 13 lower), primarily PC, PE, PP in the 20–100 µm range.
• LDIR differentiated synthetic polymers from cellulosic fibers and other natural materials, eliminating false positives.

Benefits and Practical Applications

• High-confidence polymer identification in complex food matrices.
• Automated, on-filter analysis minimizes solvent handling and contamination risk.
• Fast throughput suitable for routine QC and large-scale monitoring.
• Capability to distinguish microplastics from natural particles like cellulose and polyamides.

Future Trends and Potential Applications

• Incorporation of enzymatic digestion or prolonged heating for enhanced matrix cleanup.
• Expansion of spectral libraries to cover emerging polymers and additives.
• Extension to other food, beverage and environmental samples.
• Integration with AI-driven analytics for fully automated microplastic surveillance.

Conclusion

The Agilent 8700 LDIR Chemical Imaging System with Clarity software offers a streamlined, accurate approach for quantifying microplastics in infant formula. Direct on-filter analysis and rigorous reagent QC ensure reliable results with minimal operator intervention, supporting effective quality control and exposure assessment.

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