Fourier Transform Infrared Spectroscopy
Fourier transform infrared spectroscopy is applicable to a wide variety of chemical
applications, such as the case of polymers and organic compounds. It is the most
used technique to identify polymer in sediment samples. It uses the infrared spectrum of emission or absorption generated using infrared radiation to excite the
sample, which allows to identify the type of plastic accurately (Frias et al. 2010;
Harrison et al. 2012; Ng and Obbard 2006; Reddy et al. 2006; Thompson et al. 2004;
Vianello et al. 2013). When the infrared radiation reaches a sample, part of the
radiation is absorbed by the sample, and another part passes through it. The resulting
information is a characteristic spectrum associated to the chemical structures
presented in the sample. In microplastic identification application, one important
advantage of Fourier transform infrared spectroscopy is it allows the analysis of
polymers without destroying the sample.
Pyrolysis-Gas Chromatography in Combination with Mass Spectrometry
Another technique that allows evaluating the chemical composition of plastic particles is pyrolysis-gas chromatography in combination with mass spectrometry. Currently, this technique is widely applied to synthetic and natural polymers. In this
technique the polymers are converted to products of lower molecular weight by the
action of heat. The composition and relative abundance of the products obtained in
the pyrolysis are characteristic for a given polymer. The correct determination of this
information allows the identification of materials that cannot be determined in any
other way. Then, this technique is based on the analysis of thermal degradation
products generated during the thermal processing of the sample (Fries et al. 2013;
Nuelle et al. 2014).
The main disadvantages of this technique are that particles must be placed
manually in the pyrolysis tube and lower particles cannot be manipulated manually.
In addition, the method lets the analysis of only one sample per test, and, therefore,
large quantities of sample are not suitable for processing. Finally, compared with
spectroscopic methods, the major disadvantage is that it is destructive.
Raman Spectroscopy
Raman spectroscopy, together with the Fourier transform infrared spectroscopy, is
another important and commonly used spectroscopy technique that provides chemical information of microplastics (Araujo et al. 2018; Cole et al. 2013; Imhof et al.
2012, 2013; Murray and Cowie 2011; Van Cauwenberghe et al. 2013). The analysis
is based on the examination of light dispersed by sample when a monochromatic
laser source (between 500 and 800 nm) impacts on it. The result is a characteristic
Raman spectrum that allows the identification of each type of polymer. It is a
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V. Godoy et al.
Fourier transform infrared spectroscopy is applicable to a wide variety of chemical
applications, such as the case of polymers and organic compounds. It is the most
used technique to identify polymer in sediment samples. It uses the infrared spectrum of emission or absorption generated using infrared radiation to excite the
sample, which allows to identify the type of plastic accurately (Frias et al. 2010;
Harrison et al. 2012; Ng and Obbard 2006; Reddy et al. 2006; Thompson et al. 2004;
Vianello et al. 2013). When the infrared radiation reaches a sample, part of the
radiation is absorbed by the sample, and another part passes through it. The resulting
information is a characteristic spectrum associated to the chemical structures
presented in the sample. In microplastic identification application, one important
advantage of Fourier transform infrared spectroscopy is it allows the analysis of
polymers without destroying the sample.
Pyrolysis-Gas Chromatography in Combination with Mass Spectrometry
Another technique that allows evaluating the chemical composition of plastic particles is pyrolysis-gas chromatography in combination with mass spectrometry. Currently, this technique is widely applied to synthetic and natural polymers. In this
technique the polymers are converted to products of lower molecular weight by the
action of heat. The composition and relative abundance of the products obtained in
the pyrolysis are characteristic for a given polymer. The correct determination of this
information allows the identification of materials that cannot be determined in any
other way. Then, this technique is based on the analysis of thermal degradation
products generated during the thermal processing of the sample (Fries et al. 2013;
Nuelle et al. 2014).
The main disadvantages of this technique are that particles must be placed
manually in the pyrolysis tube and lower particles cannot be manipulated manually.
In addition, the method lets the analysis of only one sample per test, and, therefore,
large quantities of sample are not suitable for processing. Finally, compared with
spectroscopic methods, the major disadvantage is that it is destructive.
Raman Spectroscopy
Raman spectroscopy, together with the Fourier transform infrared spectroscopy, is
another important and commonly used spectroscopy technique that provides chemical information of microplastics (Araujo et al. 2018; Cole et al. 2013; Imhof et al.
2012, 2013; Murray and Cowie 2011; Van Cauwenberghe et al. 2013). The analysis
is based on the examination of light dispersed by sample when a monochromatic
laser source (between 500 and 800 nm) impacts on it. The result is a characteristic
Raman spectrum that allows the identification of each type of polymer. It is a
10
V. Godoy et al.