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Identification of microplastics using Raman spectroscopy

Microplastics are found everywhere in the environment including oceans, fish, salt, air, rivers, bottled water and tap water. They accumulate in water and are eaten by animals such a fish and shellfish. These microplastics are then subsequently found in food and water for human consumption. There is a lot of debate and research around how dangerous microplastics are to the human body and, so far, the results are inconclusive.

Raman spectroscopy is ideal for distinguishing polymers, contaminants and dyes. Its fingerprint type analysis offers great potential as a tool in identifying microplastics in marine environments. Commonly employed techniques for studying microplastics are often limited to particle sizes above 300 µm. However, only particles smaller than 150 µm can be absorbed into the human gut and, therefore, this size range could be of vital importance. The high spatial resolution offered by confocal Raman spectroscopy means even the smallest of microplastics can be interrogated.

This application note investigates three polymers, polyethylene (PE), polytetrafluoroethylene (PTFE) and nylon-6, using the Edinburgh Instruments RM5 Raman Microscope. PE is one of the most manufactured polymers, with tens of millions of tonnes made globally each year, much of this being used in packaging, and is one of the top three most commonly found plastics in global aquatic systems. PTFE is a fluoropolymer used frequently for its non-stick properties, for example in frying pans. PTFE shares a very similar structure to PE, however, their synthesis and uses differ significantly. There have been several cases recently where perfluorooctanoic acid (one of the synthesis materials for PTFE) has been found in drinking water in the USA and Australia, this acid is a carcinogen. Nylon-6 is a polyamide which frequently finds use in the automotive industry and in fishing materials. Discarded fishing equipment provides an instant route for nylon-6 to enter the aquatic ecosystem. These three polymers were chosen for their abundance in the Earth’s oceans.