This book focuses on the detection of mercury (II) ions in aqueous solutions under the effects of electromagnetic fields. The interaction between the electric field transmitted through the test solution and the external magnetic field provided induces Lorentz forces, thus magneto-hydrodynamic (MHD) flow, which can be used to stir and mix the sample solution uniformly without the use of any mechanical moving parts or rotating electrodes. This research develops an ultra sensitive mercury sensor by combinatorial approach of MHD with analytical technique for ultrasensitive detection of mercury ions.