Identification of Microplastics Using a Custom Built Micro-Raman Spectrometer

Microplastics are plastic particles less than 5 mm in size but larger than 0.1 μm. Widespread microplastic pollution in aquatic and terrestrial environment is raising serious concern globally due to its detrimental impacts on living beings. This urge for the necessity of a sensitive analytical tool, which can facilitate reliable identification of microplastics. Micro-Raman spectroscopy enables molecular level structural details of samples and thus highly preferable for the identification of microplastics in water. Besides being a non-destructive technique enabling fast analysis, this technique requires minimal/no sample preparation. The present work demonstrates the performance of a custom built Micro-Raman spectrometer for the discrimination of various microplastics in water based samples. Micro- Raman analysis have been found quite successful in the identification of Polystyrene (PS), Polyethylene terephthalate (PET), High Density Poly ethylene (HDPE), Low Density Poly ethylene (LDPE) etc. The Micro-Raman spectral data have been capable enough for the discrimination of high-density polyethylene (HDPE,> 0.940 g/cm3) and low-density polyethylene (LDPE,< 0.930 g/cm3) microplastics, especially due to the variations in the C-H stretching vibrations (2825-2970 cm-1). The ratio of intensities of asymmetric CH2 stretching mode (2879 cm-1) and the symmetric CH2 stretching mode (2847 cm-1) are found to be higher for HDPE with respect to LDPE. Moreover, intensity variations were also observed for the antisymmetric and symmetric C-C stretching bands present at 1059 cm-1 and 1126 cm-1 respectively. The band at 1167 cm-1 arising from CH vibration have also shown an intensity enhancement in HDPE samples.