Electrical mobility

The ion mobility is defined in the physical chemistry as the mobility of the ions in a solvent at a given temperature, the drift velocity and the electric field strength. The ion mobility is thus the rate of migration of ions of a given species in water at 25 ° C ( 298 K) in an electric field of 1 V / m at.

The mobility of dissolved ions depends on their size, charge, hydration and other interactions with the solvent. The ion mobility often of inorganic cations and anions is in the range of about 5.10 -8 m 2 / ( s · V). Conspicuous are two exceptions, the hydroxide ions and hydronium ions which have a four - or seven times higher mobility. This is due to the formation of hydrogen bonds and ion migration through the Grotthuss mechanism.

With the ion mobility, the specific conductivity of the electrolyte is related.

Different ion mobility is used in different electrophoresis methods for separating ionic substances in an electric field and, for example, be sent separately to a measurement.

Mobilities of some ions in m2 / (s · V):

The mobility of ions in the electric field is described by the Einstein - Smoluchowski relation in conjunction with the diffusion coefficient of the first Fick law. This representation is also referred to occasionally as " the Nernst -Einstein relationship."


  • Charge of the particles,
  • The Boltzmann constant,
  • Is the absolute temperature,
  • Diffusion coefficient of the particles in the medium

The ion mobility in gas phase plays an essential role in the analytical instruments, such as ion mobility spectrometers. Here, the variation of ion drift velocity is used in an external electric field, in order to achieve separation of different analytes in accordance with the ionization.