Dear Najat El-Kurdi , most common plastics show rich IR spectra, so this technique is a good one to detect and quantify plastics. The main difference between FTIR and micro-FTIR is the way to excite the sample. With FTIR you need your sample in a cuvette (if liquid or aerosol) , mixed with KBr powder in the shape of a pellet or deposited over a KBr crystal. In all these cases you place your sample in the optical path of your instrument and then the laser beam pass through the whole sample, so that some light will be part of te original beam and part will be the radiation emitted by your sample.

With micro FTIR, you need a microsope to focus the laser beam on your sample. Generally this will work better with solid samples or thin films of liquid samples. The information you get comes mainly from the focal point and it could change abruptly when you displaces your sample or the laser beam from a point to another in the same sample. Imagine you have a tiny piece of plastic, now focus your laser on it, get the spectra, and now you shift the sample some microns away from the plastic particle, now you will not get a plastic spectrum. Of course if you have a larger piece of plastic that is homogeneous in its composition, when you focus on a position of it or another, you should get the same spectra in both positions or any other point into the plastic piece.

FTIR gives you an average information from a sample that has been homogeneized while the micro-FTIR normally let you get a localized information about a particular point in your sample.

Hope this helps. Thanks for asking and good luck with your research work.

Dear Najat El-Kurdi,

Manuel Gómez certainly explained very well the fundamentals and differences of FTIR and micro-FTIR techniques.

I would like to complement by saying that for FTIR, another valid option would be performing it using ATR mode (attenuated total reflectance). This way, the preparation of the KBr pellet is avoidable, since you can perform measurements directly on solid or liquid samples. But I guess it would be difficult to detect microplastics in a sample, because the information would be related to the whole sampling area.

Moreover, about micro-FTIR, which is a very nice 2D imaging technique with spatial resolution, I think it could provide interesting compositional mapping with adequate sampling resolution to allow for microplastic detection (this paper is an example: Article Microplastics in the Black Sea sediments

Good work all and have a nice day!

Manuel Gómez certainly explained very well. But the Fourier Transform InfraRed uses broad spectra of a thermal light source (Globar). Fourier Transform-Raman uses laser light sources. The spatial resolution of a modern Raman system reaches 400 nm. FTIR resolution limited by wavelength - approx. 10microns. Of course, high spatial resolution is only necessary if you want to identify individual particles.

Preprint Microplastics, an Emerging Concern: A Review of Analytical T...