Langmuir probe measurements are performed in magnetized expanding plasmas of different eompositions. The influence of the magnetic field on the currents collected by the probe in an argon plasma is investigated at two different flows and for two different probe sizes. The experimental results are compared to existing theories. The theoretically predicted dependence of the ratio of electron to ion saturation current on probe diameter is not observed. An empirically derived function is fitted to the data. Under the assumption that the function fitted to the results in argon is valid for other plasmas, it is possible to determine relative ion densities in magnetized nitrogen and hydrogen plasmas. It is found that the dominant ionic species in both plasmas is the atomic ion (N+ and H+. respectively).