Dioxins: Identification of microplastics in water and food using pyrolysis GC with high resolution Orbitrap mass spectrometry

Significance of the topic

Microplastics infiltration into water and food raises health concerns due to their ability to carry toxic additives and environmental pollutants. Reliable detection methods are essential for monitoring contamination and safeguarding public health.

Objectives and Study Overview

This study aims to evaluate pyrolysis–gas chromatography coupled with high-resolution Orbitrap mass spectrometry for identifying common polymer contaminants in milk, meat, and environmental waters. The approach seeks high throughput and sensitivity to detect micro- and nanoplastic particles below the limits of optical techniques.

Methodology

• Sample Preparation
  • Stormwater samples (1 L) spiked with deuterated polystyrene, filtered through 1 μm and 0.7 μm glass fiber filters to collect particulates.
  • Milk and beef samples freeze-dried, milled, spiked with deuterated polystyrene, and extracted via pressurized liquid extraction with dichloromethane.
• Analytical Technique
  • Pyrolysis gas chromatography using Frontier multi shot pyrolizer coupled to a Thermo Scientific TRACE™ 1310 GC and Orbitrap Exploris GC 240 MS.
  • Thermal desorption to reduce background interference.
  • Data processed with Compound Discoverer™ and Chromeleon™ software, employing high-resolution accurate mass (HRAM) libraries for targeted screening.

Instrumentation

• Thermo Scientific Orbitrap Exploris GC 240 mass spectrometer
• Frontier multi shot pyrolizer
• Thermo Scientific TRACE™ 1310 gas chromatograph
• Thermo Scientific Dionex ASE™ 350 Accelerated Solvent Extractor

Main Results and Discussion

• Thermal desorption effectively lowered matrix background, facilitating polymer signature detection.
• Stormwater analysis revealed characteristic pyrolysis fragments of polyvinyl chloride (benzene, naphthalene, fluorene), confirming PVC contamination.
• Milk and beef samples showed styrene, allylbenzene, α-methylstyrene, and toluene peaks indicative of polystyrene; absence of styrene dimers and trimers prevented definitive confirmation.
• High mass resolution (±5 ppm) significantly improved selectivity compared to nominal mass extraction windows simulated for single quadrupole systems.

Benefits and Practical Applications

• Combines sensitivity and selectivity to detect microplastics below optical microscopy limits.
• Enables high sample throughput through automated pyrolysis and targeted data processing.
• Versatile for environmental monitoring and food safety laboratories seeking rapid screening of polymer pollutants.

Future Trends and Potential Applications

• Integration of advanced spectral libraries and machine learning to automate microplastic identification.
• Expansion to a wider range of polymer types, including emerging bioplastics.
• Coupling with isotopic labeling strategies for source apportionment studies.
• Miniaturization and field-deployable pyrolysis-GC-MS systems for on-site monitoring.

Conclusion

Pyrolysis-GC–Orbitrap MS offers a powerful platform for detecting and identifying microplastics in complex matrices with high sensitivity and throughput. The method holds promise for routine monitoring in environmental and food safety contexts.