Development of a novel semi-automated analytical system of microplastics using reflectance-FTIR spectrometry: designed for the analysis of large microplastics

Abstract

The (semi-) automation of microplastic analysis would dramatically accelerate the otherwise time-consuming and labor-intensive process, enabling more efficient identification of global microplastic distribution. Numerous methods have been proposed for the automated analysis of small microplastics (approximately less than 100 μm) on filters using micro-FTIR (Fourier Transform Infrared Spectroscopy). However, the development of automated analysis technology for relatively larger microplastics (e.g., >500 μm), which can be handled with forceps, has progressed relatively slowly. In this study, we developed a device that enables semi-automated analysis of such large microplastics. This device modifies the reflection measurement accessory of FTIR for microplastic analysis and integrates it with an image recognition camera and a motorized stage. This system allows for the final output of the number, size, and polymer type of microplastics placed on a sample plate into a Microsoft Excel file in a single procedure. The accuracy rate of identifying degraded microplastics (comprising eight types of polymers) collected from environmental sources, including the ocean, using this device was over 98% when compared to the commonly used ATR (Attenuated Total Reflection)-FTIR method. Furthermore, the time required for analysis—from the placement of the sample and size measurement to material identification—was, on average, 6.6 times faster than conventional methods. The current MARS system can reliably and automatically identify environmentally degraded microplastics with a minimum size threshold of 400 μm, and it offers significant advantages in terms of reduced data collection time and high throughput for the processing of large microplastics.