Abstract: Disclosed is a device for qualitative and quantitative in-vitro or in-vivo analysis of a sample by means of ATC (Attenuated Total Reflectance) while utilizing at least one radiation source, an ATR element as well as a detector unit. The present invention is distinguished by the combination of the following features: the radiation source generating a primary beam aimed at the ATR element, the primary beam impinging on the ATR element at an angle of .alpha., which is larger than the critical angle of the total reflectance .alpha..sub.T at the interface between an optically dense medium and a less dense one; the to-be-analyzed sample whose layer near the surface interacts with the primary radiation can be disposed on at least one side of the ATR element, a detector unit corresponding to the incidence angle of said primary radiation in the ATR element detects the radiation emitted from the ATR element.