Langmuir probe measurements are performed in magnetized expanding plasmas of different compositions. Under the assumption that a function fitted to results in argon is valid in other plasmas, it is possible to investigate the
influence of the magnetic field in nitrogen and hydrogen plasmas. It is found that the electron density in nitrogen can be increased by a factor of 10 by the application of a magnetic field of 4.5 mT. In hydrogen the density can be
increased by a factor of 100 by a magnetic field of 20 mT. The dominant ionic species in the magnetized nitrogen and hydrogen plasmas is found to be the atomic ion (N+and H+, respectively).