Abstract: A method for routine identification of materials of plastic components with the assistance of infrared spectroscopy with which an infrared reflection spectrum is taken from the surface of a plastic component to be investigated and compared to a set of reference spectra, whereby the material of the plastic component under investigation is correlated to a class of plastic materials represented by one of the reference spectrum, is characterized in that the plastic component under investigation is positioned with the assistance of a video device (25, 26) and in that the infrared reflection spectrum is recorded in the range of the mid-infrared (MIR) in a wave length region between 400 and 4,000 cm.sup.-1. In this fashion even plastics which, for example, are filled with carbon can be routinely identified. It is preferred when the first derivative of the recorded IR spectrum with respect to wave number is taken and compared to the first derivative of the IR spectra of the reference spectra.

Abstract: An auxiliary device enabling reflection measurements to be carried out by an IR spectrometer designed for the performance of transmission measurements comprises two deflecting mirrors (22, 23) to be positioned in the straight beam section of the spectrometer and two focussing reflector arrangements (26, 2, 27) of which the first forms at the location of the sample (16) to be investigated by the reflection method a reduced image of the focus (30) situated within the ray of beams (28) deflected by the first deflecting mirror (22) while the said second focussing reflector arrangement forms an enlarged image of the said reduced focus at a distance before the said second deflecting mirror (23) so that the beam of rays (33) emitted by the said second deflecting mirror forms a prolongation of the beam of rays inciding upon the said first deflecting mirror just as if the auxiliary device did not exist.