A positioning device for optimal positioning of infrared accessories, usable in all FTIR spectrometers, in the X-Y-Z planes of the spectrometer with an additional angular adjustment in the X-Y plane in order to optimize the infrared energy reaching the spectrometer detector. All accessories are mounted on the sample stage of the positioning device by means of a single positioning pin and all accessories are equipped with a blocking shield which assures that all energy which reaches the detector of the spectrometer has transited the attenuated total reflectance crystal.