WCPS: Investigation of Microplastic Size and Number Changes During Simulated UV-Degradation Using Single Particle ICP-MS/MS

Significance of the Topic

The persistence of microplastics (MPs) in aquatic and terrestrial environments poses serious ecological and human health concerns. Reliable quantification of MP size distributions and number concentrations, especially in the sub-micrometer to micrometer range, is critical to understand fragmentation dynamics, transport behavior, and potential risks. Single particle inductively coupled plasma tandem mass spectrometry (spICP-MS/MS) offers a promising analytical approach to address these challenges by enabling high-throughput, element-specific particle detection.

Objectives and Study Overview

This study aimed to develop and apply an Agilent 8900 ICP-QQQ spICP-MS/MS method using 13C detection to track changes in particle size and number concentration of polystyrene (PS) microplastics during simulated UV-degradation. Key goals included establishing calibration across a wide particle size range (0.8–5 μm), determining nebulization efficiency and detection limits, and monitoring the fragmentation kinetics under controlled UV exposure.

Methodology

• Preparation of PS microplastic suspensions at nominal diameters of 0.8, 1.0, 1.8, 3.0, and 5.0 μm via multistep dilution in 18.2 MΩ·cm deionized water and homogenization by stirring, ultrasonication, and vortexing.
• Simulated UV-degradation: suspensions exposed to a 36 W UV lamp for 0, 12, 16, and 20 h with continuous stirring to prevent settling. Aliquots were collected at each time point.
• spICP-MS/MS analysis: 13C measured in MS/MS no-gas mode (Q1 = Q2 = m/z 13) to improve signal-to-noise and minimize interference from 12C. Data acquisition used 0.1 ms dwell time over 60 s per run.
• Calibration: mean counts per second (CPS) plotted against particle volume yielded a linear response (R2 = 0.9999) across 0.8–5 μm, establishing size quantification parameters.

Applied Instrumentation

• Agilent 8900 Tr​iple Quadrupole ICP-MS (ICP-QQQ) equipped with MicroMist glass concentric nebulizer, quartz spray chamber, quartz torch (1.0 mm i.d.), and nickel interface cones.
• Self-aspiration via 0.51 mm i.d. PTFE tubing; sample inlet flow ~0.08 mL/min; nebulizer gas ~0.78 L/min.
• Instrument settings: RF power 1600 W; sampling depth 6 mm; KED 5 V; Q1 and Q2 at m/z 13; acquisition time 60 s. Single Particle module in MassHunter v5.1 handled calibration and particle calculations.

Key Findings and Discussion

• Particle size calibration: strong linearity between CPS and particle volume confirmed accurate sizing from 0.8 to 5 μm. Background 13C signals limit the lower size detection boundary.
• Nebulization efficiency (ηneb) varied with particle size from ~1.9% (0.8 μm) down to ~0.5% (5 μm), resulting in number concentration limits of detection (LODs) between 2.0×106 and 6.9×106 particles/L.
• Mixed-size discrimination: a mixture of 1.8, 3, and 5 μm PS beads at mass ratios 1:4.6:20.1 produced distinct CPS populations, demonstrating the method’s capability to resolve multiple size classes in a single run.
• UV-degradation dynamics: initial 5 μm suspensions (total ~1.87×108 particles/L) showed progressive fragmentation. After 20 h, total particle counts rose to ~5.74×108 particles/L, with a substantial shift toward sub-micrometer (0.8–1.8 μm) fragments, revealing rapid secondary MP formation.

Benefits and Practical Applications

• Enables quantitative tracking of MP fragmentation from micro- to nanoscales under simulated environmental stressors.
• Provides element-specific, high-throughput monitoring of polymer particles without complex sample prep or optical biases.
• Applicable to quality assurance in water testing, environmental monitoring, nanoplastic research, and regulatory compliance.

Future Trends and Potential Applications

• Extension to mixed polymer types using multi-element isotopic labeling or collision/reaction cell strategies.
• Integration with on-line separation (e.g., field-flow fractionation) to resolve complex environmental matrices.
• Standardization of spICP-MS/MS protocols for regulatory frameworks assessing nano- and microplastic pollution.
• Coupling with toxicological assays to correlate size-resolved particle data with biological outcomes.

Conclusion

This work demonstrates that Agilent 8900 ICP-QQQ spICP-MS/MS, targeting 13C, can accurately size and count PS microplastics across sub-micrometer to micrometer scales and track UV-induced fragmentation dynamics. The method’s sensitivity, broad dynamic range, and element specificity offer a robust analytical platform for environmental fate studies and risk assessment of micro- and nano-plastic contaminants.

References

• Javier Delgado-Gallardo et al., ACS ES&T Water, 2021, 1(4), 748–764.
• E. Bolea-Fernandez et al., Journal of Analytical Atomic Spectrometry, 2020, 35, 455–460.
• Ziyi Liu et al., Environmental Science & Technology Letters, 2022, 9(1), 50–56.