Detection method for ionic species based on the electroacoustic effect.

The development and application of a new ion detection method based on the electroacoustic (EA) effect is described. An EA signal, produced by applying a pulsed-type electric field to an electrolyte solution in an electroacoustic cell, is dependent on the electrical and thermal properties of the electrolyte and can be detected by using a conventional gas microphone system. The EA signals, generated in this fashion, are proportional to the square of the amplitude of the pulsed-type electric field and show an inverse dependence on the modulated frequency, as found in other acoustic detection systems. The results of this study demonstrate that the EA signals observed with the new system display a linear dependence on the concentration of the electrolyte over a 3 order-of-magnitude concentration range (ca. 10(-7)-10(-4) M). The detection limit of this system was shown to be as low as 29.9 ppb for an aqueous solution of HCl. The results also indicate that the EA signal is proportional to the equivalent conductivity of electrolytes in aqueous solution. As a consequence, the new method has the potential of being used as a universal detector for ions in solutions. An important property of this detection system is that it can be applied to in situ ion detection, and as a result, it can be employed in kinetic studies to follow the progress of ionic chemical reactions.