A device for detecting the concentration of a given component in a solution, preferably the concentration of urea in solution with water includes a means for emitting radiation, at least one means for receiving radiation, which is prearranged for determining at least one characteristic of the radiation, and a light guide, which is prearranged for optically connecting the emitting means to the receiving means, wherein the light guide has at least one surface that is to come into contact with the solution so as to determine an interface of separation between the propagation medium and the solution. Control means are configured for obtaining a value indicating the concentration of the compound in the solution as a function of the signal coming from the receiving means.