General Principles of Voltammetry

The instrumentation for voltammetric measurements consists of two main parts the electronics, mostly a polarograph, and the electrochemical cell. 

The electronics consist of a very stabilized voltage source (potentiostat), devices for the superimposition of different pulses and waves, timer for synchronization, amplifier for the measurement of current in the range of picoamperes to milliamperes, recording units like x/t or x/y recorders, visible display unit (VDU), and printer. In modem instmments the use of microprocessors and computers has resulted not only in simplification of the voltammetric measurement but also in an increase in the accuracy and precision of the analyses. 

The electrochemical cell consists of a vessel of appropriate size (from a few jjlL to several mL) containing a mixture of the supporting electrolyte and the solution to be analyzed in which the working electrode, the reference electrode, the auxiliary electrode, a gas inlet tube, and a stirring device are immersed. 

Working electrodes (WEs) are those at which the electrode processes occur. They are usually made of an inert material which is not affected by electrode reactions. Different kinds of working electrodes can be used for voltammetric analyses. The choice of the electrode depends on the metal to be determined, on the kind of accumulation to be used, as well as on the voltage range to be applied. 

Nowadays there are two main types of stationary mercury electrodes. One type consists of a capillary joint to a displacement vessel into which a micrometer gauge rod is screwed. The drop size is determined by the screw thread of the micrometer and the rotation [6]. The other type uses a microvalve (needle valve or flat valve) instead of the micrometer rod to determine the drop size by the time the valve is opened (usually a few msec). 

---