In some cases you want to carry out your measurements in the field, in several places and have results available immediately. That is why PalmSens has developed a portable battery-powered potentiostat and a USB-powered potentiostat that you can connect directly to your phone.
An impedance analyzer is a device that can measure how a particular substance or electrode surface responds to a a potential that is constantly increased and decreased within certain predefined limits (a potential wave).
If you want to apply a current to a liquid, such as mercury, and want to observe the change of potential, you need a device that can control the former and measure the latter. Such a device is called a galvanostat.
If you want to do electrochemical measurements with a specific purpose in mind, you may need an economically priced potentiostat. Palmsens has several attractively priced instruments for you.