Quantitative Analysis Of Microplastics By TGA-FTIR-GC/MS

Microplastic is a new type of global pollutant with small size,wide distribution,easy to be eaten by organisms and accumulated in the food chain.As a global pollutant,microplastic is not only a source of environmental pollutants,but also a carrier for toxic pollutants.The ecological risk and food safety caused by microplastic pollution in the environment had became a research hotspot.However,the lack of accurate and efficient microplastic qualitative and quantitative analysis methods had become one of the bottlenecks of the above research.TGA-FTIR-GC/MS integrated the latest thermal gravimetric,spectroscopic,chromatographic and mass spectrometry technologies.It could not only obtain the real-time weight loss information,but also obtain the corresponding infrared spectra.It could also separate and qualitatively the complex pyrolysis products produced at a certain temperature by gas chromatography-mass spectrometry,which had great research value for the control of the characteristics of micro-plastics and the confirmation of information analysis.So,this research developed the microplastics quantitative analysis method by TGA-FTIR-GC/MS based on the common plastics such as polyethylene,polypropylene,polyvinyl chloride,polystyrene and polymethyl methacrylate.It was the first time to develop a quantitative analysis method for microplastics by TGA-FTIR-GC/MS.Some parameters of experimental conditions were blank.Taking polystyrene microplastics as an example,the effects of heating rate,atmosphere and gas flow rate on the pyrolysis behavior of microplastics were investigated.The FTIR characterization was used to observe the changes of product functional groups during pyrolysis of microplastics.GC/MS collected pyrolysis products at different temperatures to analyze changes in the product duringmicroplastics pyrolysis.The results showed that the microplastic pyrolysis product would not change during the pyrolysis process,but the concentration was proportional to the severity of the pyrolysis reaction.The experimental conditions were finally determined through the comprehensive analysis of the data produced by TGA,FTIR and GC/MS.The pyrolysis products of microplastics were complex and diverse.The precondition of establishing quantitative analysis method of microplastics by TGA-FTIR-GC/MS was to deeply understand the pyrolysis behavior of different microplastics.Under the best experimental conditions,the pyrolysis behavior of polyethylene,polypropylene,polyvinyl chloride,polystyrene and polymethyl methacrylate microplastics were investigated.The results showed that except for the weight loss process of polyvinyl chloride,other microplastics had only one weight loss process,and the microplastic pyrolysis products were closely related to the types of microplastics.The pyrolysis products of polyethylene were mainly alkanes,olefins and diolefins.the pyrolysis products of polystyrene were mainly styrene monomers and dimers.the pyrolysis products of polypropylene were mainly composed of methyl olefins and alkadienes.The pyrolysis product of polyvinyl chloride were mainly composed of hydrogen chloride,benzene and aromatic compounds.The pyrolysis products of polymethyl methacrylate were mainly composed of mainly methyl methacrylate and butyl acrylate.According to the specificity and abundance of different types of microplastic pyrolysis products,an indicator for establishing a quantitative analysis method for microplastics were determined.The indicators of polyethylene were alkane and olefin.The indicator of polystyrene were styrene and its dimer.The indicator of polypropylene were 2,4-dimethylhept-1-ene.The indicator of polyvinyl chloride were naphthalene.The indicator of polymethyl methacrylate were methyl methacrylate and butyl acrylate.Based on the relationship between the area of indicators ions and the mass of microplastics,a quantitative analysis method based on TGA-FTIR-GC/MS was established.The results of methodological and practical tests show that the method is rapid,efficient,with low quantitative limit,and can simultaneously detect various types of microplastics in different environments.Appropriate indicators and treatment methods should be selected for samples with different substrates.Otherwise the test results may be biased.This method can be complementary to the established micro-infrared and micro-Raman spectroscopy,and has a good application prospect in the field of micro-plastics detection.