CHALLENGES IN MICROPLASTICS IDENTIFICATION IS ONE DETECTION METHOD ENOUGH? ANNA ELERT, ROLAND BECKER, ERIK DÜMICHEN, PAUL EISENTRAUT, JANA FALKENHAGEN, HEINZ STURM, ULRIKE BRAUN Federal Institute for Material Research and Testing (BAM) Berlin
Motivation: - MPs: how big is that problem? Sampling methods Sample preparations Analysis - Need to compare the results Harmonization of the methods METHODS: Optical Microscopy Spectroscopic: (Raman, FTIR) Chemical Extraction: TED-GC-MS, SEC 2
Reference material OPTICAL MICROSCOPE DLS MP after cryo-milling Soil reference material (<125 µm) contains of 1% PE,PP,,PET Courtesy of Dr. K. Altmann 3
Spectroscopic Methods: Confocal Raman Microscope Basic Information Spectra resolution < 3cm -1, Pixel resolution 0,5 µm Different wavelengths Maximum scan size 1800µm x 2000µm (190x200µm) Witec Alpha 300 4
Raman Counts Raman counts Results: Raman imaging PE PET PE PET 3000 2500 2000 1500 1000 500 PP 3000 2500 2000 1500 1000 500 PP 3000 2500 2000 1500 1000 500 Raman shift (cm -1 ) 3000 2500 2000 1500 1000 500 Raman shift (cm -1 ) More detail information about chemistry on the surface of particles Time consuming (finding particles) Fluorescence 5
170µm Spectroscopic Methods: FTIR Microscope (Transmission Mode) Agilent Technologies Basic Information 170µm One FPA field FPA detector: 4,096 spectra can be measured simultaneously covering sample areas 170x 170µm (1 FPA field) pixel resolution of 2.7 µm. Maximum scan size: 961 FPA fields 5.27x 5.27mm Brucker Hyperion 3000 µm 5
Results: FTIR imaging PE PP PE PP Integration for PP/PE 3020-2770 cm -1 PET Integration for 3124-3080 cm -1 Integration for PET 1769-1630 cm -1 Optical image 15x PET 3500 3000 2500 2000 1500 1000 Wavenumber 1/cm Chemical image NO PET detected PE PP PP PP 3500 3000 2500 2000 1500 1000 Wavenumber 1/cm Big area up to 4x3 mm Poor signal to noise ratio Sample thickness less 100µm Long acquisition times (6h) Poor reproducibility 7
Absorbance Comparison between RAMAN and FTIR in transmission Wesch C., Elert A-M., Wörner M., Braun U., Klein R., Paulus M., Scientific Reports, 2017 accepted FTIR 50µm 1.5 C=O C=C 1611 No. 55 PP (ref) 1.0 1740 0.5 0.0 3500 3000 2500 2000 1500 1000 RAMAN C=C C-O-C PP Ref No. 55 Wavenumber (1/cm) 1614 Raman more surface sensitive Aging status 1459 Optical image x20 3500 3000 2500 2000 1500 1000 500 rel. 1/cm 8
Chemical Extraction Method TED-GC-MS Basic Information Identification via decomposition products Sample amount: 20-50 mg, 300-600 C, 10 K/min, 30 ml/min N 2 Good results (PP, PE, ) Polymer LOD in µg PE 1,6 PP 0,44 0,20 PET 0,68 PA6 0,52 E. Dümichen et al., Assessment of a new method for the analysis of decomposition gases of polymers by a combining thermogravimetric solid-phase extraction and thermal desorption gas chromatography mass spectrometry, Journal of Chromatography A 1354 (2014) 117-128 PA6.6 2,8 PMMA 0,20 SBR 0,27 9
Results: TED-GC-MS m/ z 105 +Isomers m/ z 69 m/ z 55 m/ z 91 RM# 1 Good reproducibility Fast analysis (YES/NO) No preparation needed reference No information about size or aging status of particles PET PP PE 12 13 17 18 21 22 26 27 28 Retention time (min) Possible quantification! 10
Chemical Extraction Methods Size Exclusive Chromatography SEC Basic Information Solvents: THF for and HFIP for PET, PP and PE need high temp. SEC Sample amount 500mg Agilent 1100 Detection of extract with IR ATR 11
W(log M) W(log M) area Results: SEM and RP-LC (quantification) 1.2 1.0 Microplastic in Soil - RM #1 PET 1.2 1.0 Microplastic in Soil - RM #1 6000 Recovery rate 99% 0.8 0.6 0.8 0.6 4000 0.4 0.2 0.4 0.2 2000 RM#1 0.0 10 3 10 4 10 5 10 6 Molmasse [g/mol] 0.0 10 3 10 4 10 5 10 6 Molmasse [g/mol] 0,5 1,0 1,5 2,0 2,5 3,0 3,5 concentration [mg/ml] PET PET [g mol -1 ] from Ref. from RM Ref. RM M w 92.5 93.0 208.7 205.7 Big amount of sample Information about Mw distribution Quantification possible Only PET, (for PP, PE high temp. SEC) No information about size of particles Polymer has to be dissolved Information about degradation status 12
Result information Assesment of the methods Parameters Sample amount Raman Chemical FTIR imaging TED-GC-MS scanning extraction 1 µg 1 mg 20 mg 500 mg Sample preparation Single particle Single particle layer on IR transparent As received As received substrates Measurement time for representative results ~ 40 min 3-6 h 3 h 2 h Identification PE, PP,, PET PE, PP,, PET PE, PP,, PET, PET Quantification No No Yes Yes Particle size Yes Yes No No distribution Aging Status Yes Yes/No No Yes 13
Summary Scientific question what information need to be known before analysis TED-GC-MS, SEC fast and quantitative analysis Spectroscopy (FTIR, RAMAN) particle size, more detail analysis Combination of several parallel approaches - broader understanding 14
Acknowledgement: BAM, TF Microplastics Team THANK YOU FOR YOUR ATTENTION!