Research in micro plastics is a current trend in scientific research in the environmental area, circular economy and water resources. The detection of polymers from different matrices has relevance for the development of methodologies that make it possible to obtain a useful technique for standardization in the analysis of microplastics. The objective of this research is the detection of polymers by infrared microscopy, which is a method that uses the Fourier transform and that interprets the signals resulting from the vibration of particles of the polymeric samples of the physical–chemical degradation coming from river and biological from Tenebio molitor. The samples taken from frass and river water went through digestion to obtain the polymers, they were analyzed by reflection tests, a spectral analysis and a comparison by libraries were obtained to identify their chemical structure. The OMNIC Picta software tools were used, which resulted in count and area data that occupy the total frass and river samples, distinguishing the chemical structure of each polymer. The chemical identity of the microplastics sampled from the different matrices was obtained, thus demonstrating the power of the method to obtain a structural understanding of polymer degradation in controlled environments such as the polymer biodegradation process by T. molitor and natural environments in the degradation samples due to physicochemical effects in water matrices.