Abstract: A method is disclosed for identifying the presence or concentration of a target species in a sample by transmitting a wave of ultrasonic vibration through the sample and calculating, from measured values for time of flight of the wave through the sample and its attenuation during that time, an identification parameter dependent on the type or concentration of the target species in the sample and independent of the distance travelled by the wave through the sample. The method is more convenient to use than existing identification techniques because of the removal of distance from the measurements and calculations necessary. The method is of particular use in identifying polymers, for example, in reclamation and recycling processes. An apparatus for performing the method is also disclosed.