A reliable ion-chromatographic (IC) method with a novel double chamber bulk acoustic wave (DCBAW) detector was developed for monitoring five important inorganic cations (Na(+), K(+), NH(4)(+), Ca(2+), Mg(2+)) in biological culture media. A Shimpack IC-C1 analytical column with 5 mM hydrochloric acid and 2 mM acetonitrile as mobile phase was used. All investigated inorganic cations could be detected and qualified in the range of 0.1-100 mg/l. Results showed that the consumption velocities of Mg(2+) and K(+) are related to the growth of the cells and decrease fastest during the first 2-5 h. Mg became a growth limiting factor at concentration below 0.1 mg/l. The concentrations of the other cations stayed nearly constant during the whole fermentation process. The simple sample preparation, short analytical time and accurate results made it a useful tool for the on-line monitoring, controlling and optimization of the fermentation process.