Analysis of Microplastics

July 8, 2021

Microplastics are possibly the greatest hazard to the environment since the ozone layer depletion and global warming. Unfortunately for life on Earth, microplastics are now spread across the entire planet. The race is on to identify the nature, cause, and effects of these materials, and to find suitable remedies for environmental clean-up.

Scientists are now studying details of the global distribution of microplastics. Plastics are easily ground down into micro particles by environmental action, such as oceanic movement. As a result, microplastics are not just found in the environment, but also the entire food chain.

There are many analytical techniques being used, but one of the most important is molecular spectroscopy, and in particular, the vibrational measurements offered by Raman and IR. This makes microscopy an extremely important tool, not only in the identification of chemical composition, but also the shape and size distribution. When IR and Raman Microscopy are used, the physical nature of the particles can be observed together with the distribution and chemical composition.

Raman Microscopy

Confocal Raman microscopy is a great technique for microplastics as it is non-contact and non-destructive, the observation can be made simply using low power objectives over a wide field of view, or with a high power objective on smaller particles. Mixed samples including inorganics can be identified.  Spectral libraries can be used for component identification.

NRS-4500 Raman spectrometer

Infrared Microscopy Microscopy is probably more suited to large particle sizes, greater than 10 microns. The transmission allows for reduced sample prep and non-contact sampling, but ATR is also useful for mapping larger particles and for mixed polymer materials. The larger IR spectral databases of organic substances is a major attraction to users when identifying unknown foreign materials.

FT/IR-6700 + IRT-7200 IR microscope system

FTIR-ATR Spectroscopy

ATR offers a “preparation-free” measurement of samples and is ideally suited to plastic particles as they deform well and make good contact with the prism under pressure. Diamond is an excellent prism material as it is virtually indestructible and is transparent to visible light, which can be used for sample observation. For microplastics that are large enough to be measured without a microscope, chemical identification is easy with a typical ATR, and the ATR ProOne View also provides a visual record of the particles being measured.

ATR accessory