A novel approach for the quantification of the mass of micro and nanoplastic particles from filter samples

The widespread use and improper disposal of plastics have led to significant pollution in oceans, rivers, and landfills by these materials. This pollution threatens biodiversity and the health of ecosystems. Improperly disposed, large plastic waste may breakdown into small microplastics (5mm), which enter the food chain through ingestion by wildlife and thus also poses a serious concern to humans.

Traditionally, the detection of these particles is almost exclusively carried out by spectroscopic methods, such as infrared and Raman spectroscopy, while electron microscopy and thermoanalytical methods are not widely used tools in microplastic studies. This leads to major knowledge gaps in the degradation and environmental fate of plastic pollution, particularly for nanoplastic particles since the most used spectroscopic and visual detection methods have lower spatial resolution of ca. 20 µm (FTIR) and 1 µm (Raman), leading to a lower size cut-off. This leaves a gap for thermoanalytical methods, which can analyze plastic particles regardless of their size and are able to build a relationship, effectively trading information on polymer-specific particle size distributions for information on the mass of particles of a certain polymer.

We present a novel approach that combines a multiwavelength carbon analyzer with a photoionization time-of-flight mass spectrometer for analysis of microplastic particles from quartz fiber filters. The temperature of the oven of the carbon analyzer is continuously ramped with ca 20 °C min^-1 to trigger the thermal decomposition of different plastic polymers (Figure 1 top panel). The major fraction of the evolving pyrolysis gas is passed over MnO₂ substrate, which is held at 850°C for complete oxidation of carbonaceous gases. The forming CO2 is transferred to a non-dispersive infrared spectrometer for quantification of the total carbonaceous material. A minor fraction of the evolving pyrolysis gas from the decomposition of the plastic is sampled by a photoionization mass spectrometer upstream of the MnO₂ substrate to capture the chemical composition of the evolving gases. The information of the mass spectrometer is used for specifying and quantifying individual polymer types.

Figure 1 Deconvolution of a mixture of polystyrene particles (blue), polyethylene terephthalate (yellow), and high-density polyethylene (red-orange) by the photoionization mass spectrometer. The top panel shows the sequential evolution of the individual polymers during analysis, and the lower panels show the polymer specific mass spectra used to identify the individual plastic types.