This work proposes a method to measure the I–V characteristic of a plane probe for each one of the ion species present in a low-pressure plasma, by using as the ammeter a mass spectrometer whose probe entrance can be biased at an arbitrary electric potential. From the I–V characteristic, the corresponding ion energy probability distribution function of each ion species in the plasma is obtained. Moreover, the corresponding ion temperature and the plasma potential are obtained. These results are in good agreement with those obtained from classical Langmuir probes and mass spectrometry methods.