Application of Fluorescence Microscopy Combined with Magnetic Solid-Phase Extraction for the Identification and Determination of Microplastics in River Waters

Abstract

A method is proposed for the identification and determination of microplastics, which includes their extraction with a magnetic sorbent based on reversed-phase carbon, followed by determination by fluorescence microscopy. Polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, polyurethane, polycarbonate, and polyamide fibers (Nylon) were selected as test samples. The determination method was developed using model mixtures containing several microplastics of the same type. Model mixtures of microplastics aged using abiotic and biotic environmental factors were also used. Based on an analysis of solutions containing model mixtures, the performance characteristics of the developed method were estimated. Microplastics were stained using a solution of Eosin Na (Y) in isopropyl alcohol upon heating. High variability in color within a single type of microplastic has been found, which complicates the identification process. With aging, the fluorescence intensity of most polymers decreased. The presence of colored microplastics did not significantly affect the spectral characteristics and fluorescence intensity. The problems arising in establishing the limits of detection and determination due to the specifics of fluorescence microscopy are considered. The limits of detection for microplastics are between 1.0 and 5.0 µg/L. The method for the identification and detection of microplastics was tested using river water analysis as an example. It was found that polyethylene and polypropylene predominate in water bodies; their concentrations are 94 ± 33 and 43 ± 15 μg/L, respectively. Natural water also contains polyethylene terephthalate (5 ± 2 μg/L) and polycarbonate (8 ± 3 μg/L).