PY-GCMS analysis of microplastics in environmental samples using nitrogen as an alternative carrier gas

Significance of the Topic

The widespread release and persistence of microplastics in the environment pose growing risks to ecosystems and human health. Analytical methods that can rapidly identify and quantify microplastics are essential for monitoring contamination and guiding remediation efforts. Pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) is a powerful tool for polymer analysis, and validating its performance with alternative carrier gases helps laboratories overcome helium shortages while maintaining analytical quality.

Objectives and Study Overview

This work establishes and validates a Py-GC/MS protocol using nitrogen as a carrier gas for the quantitation of twelve common microplastics. Key aims include developing calibration strategies, assessing precision, accuracy, sensitivity, and demonstrating that nitrogen can replace helium without compromising method performance.

Instrumentation Used

• Shimadzu GCMS-QP2020NX single quadrupole gas chromatograph–mass spectrometer
• Frontier Lab Py-3030D multi-shot pyrolyzer interfaced in evolved gas analysis and single-shot modes

Methodology and Analytical Protocol

Samples were prepared by weighing polymer standards mixed with calcium carbonate into small cups over a range of masses from 0.4 to 4.0 mg. Evolved gas analysis identified optimal pyrolysis temperatures between 500 °C and 600 °C, with a final single-shot temperature of 600 °C. Characteristic pyrolyzate fragments for each polymer were selected—one quantitative ion and one confirmatory ion. A six-point calibration (five-point for polystyrene) was established, and repeat calibration checks ensured stability. The lower limit of quantification (LLOQ) was defined at the lowest calibration point (0.4 mg).

Main Results and Discussion

• Calibration: Most polymers exhibited linear responses with coefficients of determination (r2) above 0.990. Polystyrene, ABS, and polyurethane required quadratic fits.
• Precision: Repeatability tests on ten replicates yielded relative standard deviations of 0.8–6.6 % at 0.4 mg and 2.0–8.4 % at 3 mg.
• Accuracy: Recoveries ranged from 102.6 % to 133.8 % at 0.4 mg and 101.3 % to 109.2 % at 3 mg (polystyrene at 3 mg was outside calibration range).
• Sensitivity: LLOQs for the twelve polymers spanned from 0.21 µg to 14.58 µg.
• Stability: After 42 injections, signal drift remained below 31 % for all analytes.

Benefits and Practical Applications

Replacing helium with nitrogen offers cost savings and alleviates supply constraints for routine microplastic monitoring. The validated method provides a fast, reliable workflow for environmental laboratories and supports ASTM standards for microplastic analysis. Its robustness and reproducibility make it suitable for quality control, regulatory compliance, and research applications.

Future Trends and Possibilities

Further developments may include:

• Extending the method to real environmental matrices (water, sediment, biota) with automated sample preparation
• Integration with high-resolution mass spectrometry for improved polymer identification and fingerprinting
• Expanding pyrolyzate libraries for emerging polymer materials
• Adopting advanced data analysis tools and machine learning for pattern recognition and quantitation

Conclusion

This study demonstrates that nitrogen can effectively replace helium in Py-GC/MS analysis of microplastics without sacrificing analytical performance. The method delivers reliable calibration, precision, accuracy, and sensitivity across twelve polymer types, offering a practical solution for laboratories facing helium shortages.