In normal configuration, the light beam samples perpendicularly the electrode surface. Normal configuration provides optical information related to the changes that take place in the solution adjacent to the electrode and on the electrode surface. The optical path length coincides with the diffusion layer thickness, which is usually in the order of micrometers. This arrangement is the most suitable when the compound of interest is deposited or adsorbed on the working electrode, because it provides information about all processes occurring on the electrode surface.
UV-Vis absorption SEC in normal arrangement can be performed using both transmission and reflection phenomena.
* Normal transmission
In normal transmission, the light beam passes through a optically transparent working electrode, collecting information about the phenomena that take place on the surface of the electrode and on the solution adjacent to it. Electrodes in this configuration must be composed of materials that have great electrical conductivity and adequate optical transparency in the spectral region of interest.
The external reflection mode was proposed to improve the sensitivity and to use non-transparent electrodes.
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* Normal reflection
In normal reflection, the light beam travels in a perpendicular direction to the working electrode surface on which the reflection occurs. The reflected beam is collected to be analyzed in the spectrometer. It is also possible to work with other incidence and collection angles. This configuration is an alternative when the working electrode is non-transparent. In this configuration, the optical path-length in solution is on the order of twice the diffusion layer thickness. It should be noticed that growth of films on the electrode surface could cause optical interference phenomena. As it is based on reflection phenomenon, in many cases reflectance is used as unit of measurement instead of absorbance.
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