Study On Raman Spectroscopy And Imaging Detection Method Of Microplastics Released From Tea Filter Bags

Microplastics（MPs）pollution is a public problem of the environment and human health.Plastic filter bags are widely used in sub-packaging of soft drinks,such as polyethylene terephthalate（PET）,polypropylene（PP）,nylon（NY）and polyethylene（PE）,which increase the pollution of MPs in food and environment.Raman imaging technology can obtain the imaging map by collecting the data on the surface of the filter membrane,which can be used to observe the number,shape,position and other information of MPs.In this study,Raman imaging combined with chemometrics was used to establish a MPs for detecting the release of tea filter bags.It provides a method for detection and monitoring of MPs released from tea filter bags.The main research contents are as follows:（1）Determine the optimal test conditions for Raman spectroscopy and imaging.Through the comparison of the Raman spectra of PET,PP and NY filter bags,the Raman spectrum conditions of the filter bags were determined,which were:785 nm laser,10%laser intensity,10 s integration time,scanning times 1.Before the Raman imaging of MPs released from teabags,the digestion and enrichment conditions of the tea soup were optimized,and 30%hydrogen peroxide was selected for 48 h of digestion,and the MPs were enriched on the glass microfiber filter（GMF）by filtration.Finally,the optimal parameters of Raman imaging were determined based on the Raman intensity and imaging effect of PET:785 nm laser,800～1800 cm^-1 spectral range,integration time 0.3 s,step size3μm×3μm.（2）A method combining Raman imaging with chemometrics for identifying MPs released from filter bags was established.The characteristic peak intensity,peak area and direct classical least squares（DCLS）were used to image MPs respectively.After comparison and analysis,it could be concluded that the Raman imaging analysis combined with DCLS was more effective and reliable for the identification of MPs.Three samples were selected and soaked at different time and temperatures.The results showed that 94%of the filter bags released MPs,and the amount and type of MPs released had no correlation with soaking time and temperature.Through microscopic and Raman imaging observations,it was found that most of the identified MPs were fragments and particles,and a few were fibrous（620～840μm）.Compared with PET and PP material filter bags,NY material filter bags have the lowest risk of releasing MPs.According to the source analysis of tea filter bags,most of the MPs were debris and particles adsorbed on the surface of filter bags and strings.（3）To explore the feasibility of pre-washing to reduce the release of MPs from filter bag to tea.The above three kinds of filter bags were selected for cleaning and soaking respectively.The filter membrane and filtrate were filtered from tea soup as objects.The MPs on the filter membrane was analyzed by Raman imaging,and the content of MPs in the filtrate was analyzed by pyrolysis-gas chromatography-mass spectrometry（Py-GC-MS）.Results the number of MPs on the filter membrane decreased with the increase of cleaning times.The quantitative curves of PET,PP,NY6 and PE were constructed,and the correlation coefficients were 0.9997,0.9901,0.9991 and 0.9919,respectively.It was known that there were smaller plastic particles in the tea soup filtrate,and it was estimated that the tea filtrate of single sample A,B and C contained 8.1～30.2μg,0.9～2.9μg and 0～4.0μg,respectively.Through the above analysis,it was confirmed that cleaning could remove the plastic which was easy to fall off from the filter bag.