Last Updated: 5/20/19 by Tim Paschkewitz
Before a new experiment can begin, the instrument circuitry must be configured to meet the needs of a particular electrochemical technique. The configuration step includes various “cell switching” actions such as adjusting the current range, selecting various filter circuits, turning on (or off) various relays, connecting the external cell to the control amplifier, choosing the mode (open circuit, potentiostat, or galvanostat) of the working electrode(s), and finally, applying the initial signal level to the working electrode(s). More on cell switching is found within the knowledgebase.
Unless careful steps are taken to minimize cell switching glitches, all of this initial commotion is likely to cause a few minor interruptions in cell control and some transient current flow at the working electrode. After a few milliseconds or so, these transients die away, and the cell comes to equilibrium with the new instrument settings.
In most cases, you do not want these instrument-induced current transients to be recorded as part of the experimental results. The purpose of the induction period is to provide a short period of time for the cell to equilibrate with the initial instrument settings before the active portion of the experiment begins. Data are not recorded during the induction period.
The default duration of the induction period is usually three (3) seconds or less. The default signal level (unless otherwise specified) is typically selected to match the initial signal level of the waveform being applied to the working electrode during the active measurement portion of the experiment. The figure below shows the induction period (and relaxation period
) controls which are normally found on the Advanced tab for an experiment specification
(but in some cases, these fields are on the Basic Tab) (see Figure 1). In this figure, an induction period with default duration and signal levels is used because the “Auto” checkbox is checked.
Figure 1. Typical Induction and Relaxation Period Settings in AfterMath
In general, the signal level applied to the working electrode(s) during the induction period should be chosen so that there is no significant current at the working electrode (i.e., a condition at which no redox process is occurring at the working electrode).
In a potentiostatic experiment
, choosing the right potential requires some prior knowledge or experience with the electrochemical system being studied.
In a galvanostatic experiment
, of course, simply choosing to apply zero amperes during the induction period will minimize the amount of electrochemical activity at the working electrode.
Immediately after the induction period duration ends, the active portion of the experiment begins. The precise point in time where the active portion of the experiment begins is taken to be time zero, and all data subsequently recorded during the experiment is time-stamped against this time zero.
If you do not wish to use the default settings for the induction period duration or signal levels, then you can uncheck the “Auto” checkbox as shown in the figure below (see Figure 2). When this box is unchecked, then you may set the duration and signal levels to any values that you wish. In the example below, the duration of the induction period has been set to 500 ms and the signal level for the working electrode has been set to 450 mV .
Figure 2. Manually Set Induction and Relaxation Period Settings
This means that as soon as the experiment begins (i.e., just after the Perform button is pressed), the working electrode will be held at 450 mV for 500 ms . During this time, no data is acquired. After the 500 ms induction period duration has passed, then the appropriate waveform for the electrochemical technique is applied to the working electrode and active measurement of the experimental results also begins.