Dc Potential Amperometry
DC Potential Amperometry (DCA) is the simplest technique on the epsilon. A constant potential is applied to the electrochemical cell, and the current response is monitored. Typical applications of this technique include amperometric titrations, amperometric sensors, flow cells (including liquid chromatography with electrochemical detection), etc. DCA is a standard technique on the epsilon. Multichannel amperometry experiments are also available through the addition of the optional bipotentiostat board.
Setting Up a DC Amperometry Experiment
The parameter values for DCA are set using the Change Parameters dialog box (Fig1) in either the Experiment menu or the pop-up menu.
Figure 1. Change Parameters dialog box for DC amperometry.
- Potential values are entered in mV, and time values are entered in minutes or seconds (selected using T-Units)
- The time resolution of the data is specified by the Sample Interval (e.g., the default condition is that a data point is recorded every second).
- The experiment can be run on a hanging mercury drop electrode (i.e., a single drop is used for the entire experiment) using a BASi® CGME by selecting CGME SMDE Mode from Cell Stand / Accessories in the Setup / Manual Settings (I/O) dialog box.
- A rotating disk experiment can be run using a BASi® RDE-2 by selecting RDE-2 from Cell Stand / Accessories in the Setup / Manual Settings (I/O) dialog box and entering the required Rotation Rate under RDE2 Rotation in the Cell dialog box.
- There are two gain stages for the current-to-voltage converter. The default values of these stages that are used for a given current Full Scale value are determined by the software. However, they can be adjusted manually using the Filter / F.S. dialog box. This dialog box is also used to change the analog Noise Filter Value settings from the default values set by the software.
- The default condition of the cell is that the cell is On (i.e., the electronics are connected to the electrodes) during the experiment, and is Offbetween experiments. However, the potential can be switched Onbetween experiments using the Cell dialog box. HOWEVER, THIS OPTION SHOULD BE USED WITH CAUTION SINCE CONNECTING OR DISCONNECTING THE ELECTRODES WHEN THE CELL IS ON CAN RESULT IN DAMAGE TO THE POTENTIOSTAT, THE CELL, AND/OR THE USER!
- A series of identical experiments on the same cell can be programmed using the MR (Multi-Run) option.
- The end of the experiment is determined by the Time Limit (although the experiment can be ended by the user before that time).
- Clicking Exit will exit the dialog box without saving any changes made to the parameter values. Any changes can be saved by clicking Apply before exiting.
- Range of allowed parameter values:
- Potential = -3275 - +3275 mV
- Sample Interval = 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30 and 60 sec
- Time Limit = 0 - 32000 (the maximum value allowed for the Time Limit is also determined by the Sample Interval, since a maximum of 64000 data points can be recorded in one experiment (e.g, the shorter the Sample Interval, the shorter the experiment)).
- Once the parameters have been set, the experiment can be started by clicking Run (either in this dialog box, in the Experiment menu, in the pop-up menu, on the Tool Bar, or using the F5 key).
The Applied Potential is determined by the redox potential of the analyte. For example, if DCA is used for EC detection for HPLC, the potential should be such that the analyte is electrolyzed at the mass-transport limited rate (as determined by hydrodynamic voltammetry). However, the increase in noise and the decrease in selectivity with increasing positive or negative potentials may also need to be considered when selecting the potential value.
