Chronoamperometry (CA) employs three electrodes in a steady solution with a square wavefunction as the input for the working electrode. The potential difference between the working and reference electrode starts out at zero, and no redox reaction can occur at the working electrode. The voltage then jumps immediately on the working electrode and the potential difference between the working and reference electrode is great enough to induce a redox reaction at the working electrode. The redox reaction immediately depletes the oxidant in the vicinity of the electrode, while increasing the reductant. The resultant density gradient leads to a flow of oxidant toward the electrode and reductant away from the electrode. This moving charge can be measures by an ammeter and is called the diffusion current. The current response to this sweep in potential is characterized by an immediate jump in current which drops off as the oxidant is depleted. The diffusion current, i(t), can then be related to the analyte concentration, C, and its diffusion coefficient, D by the following equation:
where n is the number of moles, and A is the area of the electrode. The applied potential is constant for a given time, and then drops back to its initial value. Now that there is reductant near the electrode, this initial potential will reoxidize the product from the first reaction, and a current will flow in the opposite direction. If this is a reversible process, the voltogram will have horizontal symmetry.
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