Quantitative sizing of microplastics up to 20 µm using ICP-TOFMS

Area of Science:

• Environmental Science
• Analytical Chemistry
• Materials Science

Background:

• Accurate quantification of microplastics (MPs) is crucial for environmental monitoring.
• Inductively coupled plasma-time-of-flight-mass spectrometry (ICP-TOFMS) is a powerful tool for elemental analysis, but its application to MP sizing has limitations.
• The upper size limit for MP detection using ICP-TOFMS needs to be better understood and potentially extended.

Purpose of the Study:

• To evaluate the upper size limit of microplastics measurable by ICP-TOFMS.
• To investigate the effectiveness of different sample introduction systems for extending this limit.
• To validate particle sizing using ICP-TOFMS measurements.

Main Methods:

• Tested four sample introduction systems with certified microplastic standards (polystyrene, PMMA, PVC) in suspension (3-20 µm).
• Compared pneumatic nebulization with a falling-tube device and a vertical downwards-pointing ICP-TOFMS.
• Quantified particle size using dissolved citric acid and analyzed chlorine signals for PVC particles.

Main Results:

• Pneumatic nebulization detected microplastics up to 10 µm.
• Falling-tube device and vertical ICP-TOFMS extended the upper size limit to 20 µm.
• Critical size values determined were 2.3 µm (PS), 2.4 µm (PMMA), 3.0 µm (PVC), and 3.9 µm (PVC via chlorine signal).

Conclusions:

• Sample introduction systems significantly impact the upper size limit for microplastic analysis by ICP-TOFMS.
• Falling-tube and vertical ICP-TOFMS methods enable the detection of larger microplastics up to 20 µm.
• ICP-TOFMS is a viable technique for sizing microplastics, with critical size values established for tested polymers.