A device for measuring a spectrum of a light beam in a wavelength range chosen beforehand, device called a spectrometer, the spectrum being generated by a fluid to be analyzed, the spectrometer including: at least one light source; a measurement cell including the fluid to be analyzed; a measurement detector placed on an optical pathway taken by a measurement optical beam being emitted by the light source and encountering the measurement cell; and a reference detector placed on an optical pathway taken by a reference optical beam being emitted by the light source and not encountering the measurement cell, wherein the spectrometer is borne by an automotive vehicle and includes an element for forming an incident optical beam emitted by the at least one light source, and for dividing the optical beam into a measurement beam and a reference beam, in the form of a waveguide.