differences notably arising possibly from a slight difference in catalyst loading a slight difference in the structure of the active layer or a slight difference in the compositions of the materials used to manufacture the meas this solution therefore allows very small differences to be detected which differences would not be detectable with conventional u201c quality control methods u201d in the context of a pilot mea manufacturing line this solution may be used to test the reproducibility of the meas by taking samples from a given batch or from various batches it may also be advantageous to test variation in reproducibility by injecting a stream at the cathode also containing a polluting species in the conventional case where the oxygen feed may notably take the form of an air feed it may be advantageous to inject a controlled amount of a species such as so x or no y the polluting species may be injected into one of the streams feeding the electrodes anode or cathode but may also be injected in order to act on the membrane for example nh 3 may be injected into the fuel h 2 or into the oxidant air use of this type of pollutant for example allows slight differences in the ion exchange capacity of the proton exchange membranes to be evaluated the pollutant may therefore also be ammonia ammonium ions nh 4 or any other cations able to exchange through the ionomer membrane na ca k etc the difference in performance.