Potentiostats experimental apparatus

The cell in Figure 2 is a typical apparatus used in LL studies. However, recently small interfaces, called here microinterfaces, were shown to have some experimental advantage. The purpose of this modification was to use the same advantage that the ultramicroelectrodes have. Ultramicroelectrodes help to overcome solution resistance difficulties that originate from a potential shift due to an uncompensated iR drop. As the interfacial area becomes smaller, the diffusion geometry becomes a spherically symmetric process, which means that the ratio of charge transport current versus solution resistance increases and, ultimately, renders the iR drop minimal. In ITIES studies, restriction of the interfacial area and use of a current amplifier for voltammetric studies is a viable alternative to a four-electrode potentiostat. 

Experimental facilities for dc polarography are available in most laboratories. It is strongly recommended that three-electrode circuitry is used for even the simplest experiment. Potentiostat circuits capable of dc mode experiments can be made cheaply and it is counterproductive to use old fashioned two-electrode equipment. The more advanced forms of polarography and stripping voltammetry do require that commercial apparatus be available but one piece of equipment can often be used for all the experiments. The experiments suggested are designed for the most part to occupy a three hour laboratory period. 

Figure 9 is a schematic diagram of the apparatus for a transmission experiment. A typical experimental study proceeds as follows. Conventional electrochemical techniques (usually cyclic voltammetry) are used to establish the potentials where the processes of interest occur, e.g., adsorption and desorption potentials. The working electrode potential is then modulated between these values at a low frequency (typically 10 to 10 Hz) using a computer-controlled potentiostat. The choice of modulation frequency is not critical except, of course, it should be considerably less than the time constant... 

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