Microplastics identification by IR imaging measurement

October 9, 2020


A lot of plastic wastes in marine became much serious damaging issue in recent, like not only the coastal landscape have been affected but also to damage natural ecosystem. Such plastics which are difficult to be caught in visible, so-called microplastic, which is thought that has originated from broken pieces of large plastic materials during long drifting or from additives for cosmetic functionality in facial cleanser, toothpaste and so on. Microplastics are concerned about contamination into marine organisms such as fish and shellfish and salt caused by runoff to the river and the sea, commercial drinking water and people taking them, so the amount of accumulation, the type of plastics and the impact on natural ecosystem are actively investigated.

IR microscope is one of the tools to investigate the type of microplastic. By using IR microscope, microplastics can be measured without complicated pretreatment, and distinguished the type of plastic by using the database. In addition, by IR imaging measurement, it becomes possible to analyze not only in-plate ratio calculation but also particle size.

In this application note, we analyzed the type of microplastics in water by IR microscope.


Measurement method

Microplastics in water were collected in a filter (material: Teflon), and IR imaging measurement was carried out. The measurement conditions are as follows.

Instruments: FT/IR-6600 Fourier transform infrared spectrometer , IRT-7200 Multichannel infrared microscope
Measurement mode: Transmission
Detector: Linear array detector
Measurement area: 800 x 800 μm
Measurement time: about 15 minutes


Fig. 1 shows representative spectra obtained by IR imaging measurement and database search results, Fig. 2 is the microscopic observation image of the measuring area and Fig. 3 is the chemical image created by the key band peaks that indicated by red and green arrows.

As a result of the database search, it was found that the plastics observed in the microscope observation image are polystyrene (PS) and polyethylene terephthalate (PET). In this time, Teflon peak was also detected in the spectrum because it was collected on the Teflon filter, but it was able to identify some plastics clearly. Furthermore, it could be visualized the distribution of each component by creating a chemical image.


By using IR imaging measurement, these types of plastics can be identified accurately even such microplastics that couldn’t be confirmed in visual. Currently, microplastics is generally defined as less than 5 mm, but more smaller plastics are subject to analysis. The measurement with IR microscope is effective for more than 10 µm, and Raman microscope is for smaller than 10 µm. Besides, Jasco has convenient accessory tool called IQ frame that can measure the same measurement area easily and quickly with both IR microscope and Raman microscope. And such combination analysis using IR and Raman spectrometers is expected to be a one of convenient and effective multilateral analysis method.

About the Author

Spectroscopy Group