Identification of polymer species in a complex mixture by pyrolysis-gas chromatography-atmospheric pressure chemical ionization-high resolution time-of-flight mass spectrometry as a basis for environmental microplastic analysis

Abstract

Pyrolysis-gas chromatography coupled with atmospheric pressure chemical ionization-high resolution time-of-flight mass spectrometry (Py-GC-APCI-TOFMS) was applied for the reliable identification of polymer species in a complex mixture to establish this system as a platform for environmental microplastic analysis. The method was evaluated on a model sample of mixed microplastics comprised of five major polymers: polyethylene (PE), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PSt), and poly(ethylene terephthalate) (PET). The representative ions in the mass spectra of the pyrolyzates were identified by Py-GC-APCI-TOFMS measurements of the individual polymer species. The unique APCI ionization/fragmentation process and the high mass resolution of TOFMS were exploited to confirm the presence of the respective polymer species in the extracted ion chromatograms (EICs) of the mixed sample for the selected key ions. PE and PP were successfully and uniquely identified in the mixed sample by focusing on specific fragment ions of the pyrolyzates formed during APCI (m/z 114.093 ± 0.020 and m/z 156.139 ± 0.020, respectively). The resultant EICs allowed for the specific analysis of these species, even in the presence of interfering species produced from the other polymers. Similar processes were applied to the detection of PVC, PSt, and PET in the mixed sample. These results demonstrated that Py-GC-APCI-TOFMS is a promising tool to characterize a complex mixture of environmental microplastics.