36 May / June 2021

Analysis of Microplastics in Environmental Samples by Pyrolysis/Thermal


by Nick Jones1 1

3 , Juergen Wendt1 , Stephanie Wright2 , Elena Hartner3 ,Thomas Groeger3

Leco European Application and Technology Center, Berlin (Germany) 2Imperial College, London (UK)

Helmholtz Zentrum, Munich (Germany)

Microplastics (MP) are an emerging pollutant which are widely distributed in the environment. Understanding the impact of their growing prevalence on the environment and human health is an important field of research. Analysis of MP in environmental samples is performed using various methods and instruments based either on spectroscopy or thermo-analytical methods combined with chromatographic separations. In this study, the applicability of using Pyrolysis/Thermal Desorption (Py/TD) coupled to single and multi-dimensional Gas Chromatography-Time of Flight Mass Spectrometry (GC(xGC)-TOFMS) as a tool for analysis of MP in environmental samples was evaluated by a series of proof of principle experiments using polymer standards and environmental aerosol samples.

Plastics are synthetic polymers mostly made from petrochemical sources. Starting industrially in the 1950s, the rate of production has been increasing annually. In 2019, around 368 million metric tons of plastics were produced worldwide [1].

Most plastics do not degrade. Instead, they slowly fragment into smaller particles, referred to as microplastics (MP) and nanoplastics (NP) based on the wide variability in size. Microplastics may have complex toxicological consequences for the environment and human health [2], and research activities in this field are increasing. Therefore, reliable analytical strategies for the characterisation of microplastics are needed to inform toxicology studies and extrapolate to environmental exposure.

Fourier-Transform Infrared (FTIR) and Raman spectroscopy are established techniques, which are practically useful for the identification of single microplastic particles. Unfortunately, they have well understood limitations when dealing with polymer-chemical mixtures, small particle sizes, and sample analysis time. The use of Pyrolysis (Py) and Thermal Desorption (TD) in combination with Comprehensive Gas Chromatography (GCxGC) and Time- Of-Flight Mass Spectrometry (TOF-MS) is an alternative tool for MP analysis in

environmental samples. This approach requires minimal sample preparation and provides powerful chromatographic separation with high quality deconvoluted mass spectral data allowing for MP degradation products, additives, and other complex mixtures of chemicals found in the environment to be resolved, detected and identified.

In order to demonstrate the feasibility of the selected instrument configuration, a proof of concept study was carried out.

Experimental Reference Materials

Nine polymer standards, available in fine powder or granule forms, were used: polystyrene (PS), polyvinylchloride (PVC), polyethylene (PE), polypropylene (PP), poly(bisphenol carbonate) (PC), polyethylene terephthalate (PET), polymethylmethacrylate (PMMA), nylon-6 (N6), and nylon-6,6 (N66) with average molecular weights (Mw) from 25000-35000 g/mol. The granules were mechanically ground using an analytical mill. Approximately 100-200 µg of individual or mixtures of the solid polymers were placed into deactivated micro vials, which were then placed in deactivated inlet liners without any further preparation prior to analysis.

A C7-C40 n-alkane standard was prepared

at a concentration of 10mg/L-1 calculate linear retention indices.

in order to

Environmental Aerosol Samples

‘PM10, high volume air samplers’, sited by urban road sides in London, UK and in Augsburg, Germany, were used to collect 24-hour samples of particulate matter (and associated chemicals) in aerosols with an aerodynamic diameter of <10 µm onto deactivated quartz filters with a diameter of 47mm and a pore size of 0.8 µm. After sample collection, 4-5mm diameter circular cross sections of the filter were obtained using biopsy punches and transferred to deactivated inlet liners.

Instrumentation and Methods

The reference materials and environmental aerosol samples were analysed using a LECO Pegasus®

BT 4D system equipped

with a thermal modulator and interfaced with an OPTIC-4 injector (GL Sciences BV) The sample liners were either placed manually in the OPTIC inlet or transferred automatically using a liner exchange device (LINEX). The OPTIC inlet was heated rapidly either from 40-250°C at 2°C/sec for thermal desorption analyses or from 50-600°C at 60°C/sec for pyrolysis analyses. Two GC

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