FT-IR microscopy is the most common approach found in microplastic research. The workflow is very simple, and the results offer high precision and reliability. Especially FT-IR imaging by focal-plane arrays is a state-of-the-art solution. If you want to know more about our FT-IR instrument setup look at the LUMOS II and HYPERION websites.
Depending on the sample you can either use transmission (contact free, IR light completely passes MP) or attenuated total reflectance (ATR, needs contact, IR light slightly penetrates MP surface). Measurements in reflection are also possible (contactless, IR light must pass MP twice) but will not be discussed at this point.
Transmission measurements are the standard approach but require special filters that allow IR light to freely pass to the detector. Depending on preference you can choose from Teflon (PTFE) membranes, metal mesh, silicon and aluminum oxide filters, which all have specific advantages and disadvantages. However, aluminum oxide filters are quite popular and thus will be used as an example on our website and in our videos. ATR on the other hand doesn’t need complex sample preparations or special filters. Microplastics can be directly analyzed on standard nitrocellulose filters and even on top of sediments or other complex matrices.
In the case of drinking water or beverage analysis, the liquid is filtered through an appropriate filter material and subsequently analyzed. If your analyzing river or sea water, material like wood, sand or seaweed needs to be removed by density separation. For this, salt solutions of various concentrations are used. The prepared samples should be dried thoroughly before subjected to IR analysis. In some cases, enzymatic digestion and/or treatment with H2O2 prior to sample filtration may be necessary to remove organic and biological contaminants.
The easiest way is to first detect interesting particles with visual methods and then characterize them point by point with chemical mapping. This “point-and-shoot” approach is very feasible but can require a lot of time if manual search is applied. As a result, automated visual identification is a key requirement for an effortless workflow in microplastic analysis by FT-IR mapping. After measurement, clear identification is readily available by infrared spectral reference libraries for all commonly found polymers.
Although an automatic visual detection reduces human error, this method poses the risk of missing smaller particles as their contrast might be low. To eliminate the human factor almost completely, FT-IR imaging is the safer approach. FT-IR or focal-plane array (FPA) imaging is the state-of-the-art solution to microplastic analysis. It is faster and offers a higher spatial resolution compared to single-point mapping analysis.
Usually, imaging analyzes a whole filter loaded with microplastic particles in one session. Since evaluation is carried out by chemical information only, the chance to miss smaller particles, that have low visual contrast, is significantly reduced. Please watch our video to learn more about FT-IR imaging of microplastics.
Again, it is hard to find a definitive answer to this question. Researchers such as the pioneering Alfred-Wegener-Institute and Aalborg University are relying on FPA technology. However in some cases, in which lower concentrations of microplastics are characterized, mapping experiments offer higher efficiency.
As experts in vibrational (micro) spectroscopy with a long-standing experience in MP analysis by FT-IR we support you in finding the most fitting solution to your demands in microplastic investigations. Don’t hesitate to contact us if you need more information.