Rapid, automated analysis of microplastics using laser direct infrared imaging and spectroscopy

, Kerstan Andreas.

Environmental researchers wish to measure the size, shape, and chemical identity of every plastic particle in a sample. Because smaller particles are thought to be the most biologically relevant, this analysis must extend to particles on the micron scale. Unfortunately, traditional techniques such as visual inspection are slow, manually intensive, and prone to operator bias. As a result, investigators have recently turned to chemically specific vibrational spectroscopy, which can be used in a microscope format for particle analysis at greater speeds. Spectral microscopes acquire a spectrum guided by a visible-light image to determine a particle's chemical identity along with its size and shape. Still, these instruments have drawbacks. Raman microscopes struggle to identify fluorescent particles, while array-based FTIR (Fourier transform infrared) microscopes generate a large number of spectra which are redundant or taken in the empty space between particles. Finally, the massive datasets generated by these microscopes introduce processing and storage challenges. Since IR spectroscopy is a useful method for microplastics analysis, alternative methods of generating and focusing IR light on a sample may overcome some of these difficulties with existing techniques. A Quantum Cascade Laser (QCL) is a tunable semiconductor laser than generates light in the mid-Infrared regions commonly known as the fingerprint region. Such a light source allows tight focusing of the bright infrared light at the precise center of each particle and this can facilitate rapid and accurate identification of micron-scale particles. In this paper, we present results of studies using an Infrared spectrometer utilizing a Quantum Cascade Laser for the characterization and quantitation of microplastics.

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