Combined analysis of plastic particles by Infrared and Raman microscopy

Download PDF May 10, 2021

Introduction

Figure 1. IQ Frame

Infrared microscopy (IR) and Raman microscopy are excellent methods for the analysis of molecular structure from molecular vibrations, each of these analytical method has its own distinct merits. On the one hand, there is a large database of IR spectra for organic substances, a major attraction to users when identifying unknown foreign materials. IR is also useful for the analysis of proteins that are more challenging by Raman spectroscopy. On the other hand, Raman spectroscopy is well suited to the analysis of organics, inorganic and carbon-based materials, which can be more arduous by IR.

By combining both techniques it is possible to obtain much more detailed information than from either analysis by itself. The accuracy of this comparative analysis has been dramatically improved by the newly developed IQ frame*1), an accessory in which IR and Raman measurement can be performed at exactly the same sample position (Fig. 1). To demonstrate this, in this application note, the component distribution of a sample sprayed with plastic particles was sequentially analyzed using both IR and Raman micro-spectroscopy.

Experimental

IRT-7000 FT-IR microscope
Figure 2. IR microscope system IRT-7200 + FT/IR-6700

1: IR microscopy

As a result of analyzing the component distribution of plastic particles using an FT/IR-7200 high-speed imaging linear-array IR microscope (Fig. 2), protein was found in addition to four plastics: polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS ) (Fig. 3).

Figure 3. Result of IR component analysis

 

Figure 4. Raman microscope system NRS-4500

2: Raman microscopy

Imaging measurement was performed at the same position as by IR in (Fig. 3) with a high-speed imaging Raman microscope NRS-4500QRI using EMCCD (Fig. 4). IQ Frame was used to transfer the measurement positions between the Raman and IR microscope stages.  The component distribution of the plastic particles was re-analyzed and carbon was found in addition to the four plastics previously identified by IR: polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS ) (Fig. 5).

In (Fig. 3), protein was detected in addition to the four plastics, whereas in (Fig. 5), carbon was detected without protein detection. These results are obtained because Raman spectroscopy has low detection sensitivity for protein, but it is good for carbon analysis.

Fig.5 The result of Raman component analysis

3: Overlay of the imaging results of IR and Raman analysis

As a result of the sample imaging shown in (Fig. 3) and (Fig. 5), only five components could be detected in the plastic particle sample by either IR or Raman spectroscopy separately. However, the results of combined analysis using IQ Frame indicated that six different components could be detected and imaged.

Figure 6. Overlaid image of IR and Raman

In order to visualize the complete analytical information, both sets of imaging data were overlaid (Fig. 6), this showed the protein detected by IR analysis together with the five other components, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS) and carbon detected by Raman analysis. These results demonstrate that using the strong points of both IR and Raman analysis can be combined to be more useful than a single analytical technique alone.

Reference
*1 100-AN-0016

System Configuration: IR Microscopy System
ModelDescriptionP/N
Main UnitFT/IR-6600FT/IR Spectrometer7085-J002A*2
AttachmentIRT-7200Linear Array Infrared Microscope7081-J064A*3
OptionsSH02-IRiQ Frame for IR7071-J136A*4

*2 FT/IR-4600/4700 and FT/IR-6700/6800 can also be used.
*3 IRT-5200 is also available. Please note that IPS-5000 XYZ auto stage is required for this measurement.
*4 SH02-IR+ is also available if the customer already has SH02-RM.

System Configuration: Raman Microscopy System
ModelDescriptionP/N
Main UnitNRS-4500-532QRIRaman Spectrometer with EMCCD7118-J061A*5
Options532nm Laser power upgrade (100mW) (Factory Option)6882-J207A*6
SH02-IRiQ Frame for IR7071-J137A*7

*5 NRS-5500/7500 can also be used.
*6 Using the standard laser (20 mW), the result in this note is obtained.
*7 SH02-RM+ is also available if the customer already has SH02-IR.

Measurement Conditions: IR Microscopic System
ModeTransmission mode (16x Cassegrain objective)
Resolution8 cm-1
Accumulationx1
Measurement Area
400 µm x 400 µm (12.5 μm x 12.5 µm/pixel)
Measurement Points32 x 32 points (1024 points, measurement time: approx. 10 seconds)
Measurement Conditions: Raman Microscopic System#columnspan#
Objective Lens20x
Exposure Time0.5 secs
Accumulationx1
Measurement Area
348 µm x 368 µm (4 µm x 4 µm interval)
Measurement Points88 points x 93 points (8184 points, measurement time: approx. 70 min.)

In this note, only the area used for analysis is displayed from the measured area.

Keywords

Raman microscopy, FTIR microscopy, IQ Frame, QRi, mapping, microplastics, protein

About the Author

Dr. Carlos Morillo received his Post Doc at Advanced Industrial Science & Technology in Fukuoka and was a Research Scientist at Kyushu University in Japan where he lived for several years. Carlos received his Doctor of Engineering from Kyushu University and his Masters and BS from Simon Bolivar University in Caracas Venezuela. He is an Applications Scientist at JASCO.