Vernier Go Direct Manual page 3

while the current is measured between the working electrode and the counter
electrode on the SPE.
Number of Segments: You will be able to choose from a 1-, 2-, or 3-segment
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CV. This is the number of segments in the potentiostat's waveform. The
number of segments determines the number of potentials you must set. One-
segment will be linear sweep voltammetry with simply an initial and final
potential setting. A two-segment CV will have an initial and final potential,
along with one switching potential. A three-segment CV will have an initial
and final potential, along with two switching potentials.
Potentials: You will need to set each potential to dictate the potentiostat's
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waveform, including the Initial and Final Potentials, along with applicable
Switching Potentials. To illustrate the importance of these settings, let us use
the example of a 3-segment CV. First, set the number of segments to 3. The
Initial Potential is the potential at which you wish the voltammogram to start.
In this example, we will set it to 0 mV. From here, the potential must sweep in
either a negative or positive direction from the initial potential; therefore, in
this case, Switching Potential 1 cannot be 0 mV. Setting Switching Potential 1
to +750 mV means the CVS will sweep in a positive direction from 0 mV to
+750 mV. Note: You cannot sweep more than 2000 mV in one direction and it
is not recommended to sweep more than 1600 mV in one direction. From
Switching Potential 1, the CVS must sweep in a positive or negative direction
to Switching Potential 2. Setting Switching Potential 2 to –500 mV means the
CVS will now sweep from +750 mV to -500 mV. The Final Potential is where
the CVS will conclude the experiment acquisition.
Sweep Rate: The Sweep Rate is the rate at which the individual segments
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sweeps will occur in mV/s.
Current Range: The Current Range sets the allowed current range for the CV.
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The High Current Range is ±1000 μA, Medium is ±100 μA, Low is ±10 μA,
and Lowest is ±1 μA. Setting to a lower current range will increase resolution
of your CV; however, if the current range is set too low, the CV cannot
proceed. Note: The range values are not absolute, you may be able to get some
additional current on any particular setting but this will vary from instrument
to instrument.
Bulk Electrolysis
In this setting, the potentiostat holds the potential of the working electrode at one
value and measures the resulting current over time. In this type of experiment, the
analyte is converted from its original oxidation state to a new oxidation state either
through reduction or oxidation. Analyzing the resulting data can help determine
the electric charge passed over time. The experimental parameters to set are the
potential (mV), rate (s), and duration (s).
Open-Circuit Potentiometry
This experiment is a passive experiment whereby the counter electrode circuitry of
the potentiostat is bypassed. In this mode, only the resting potential measured
between the reference and working electrode is measured. This is not to say that
the chemical system is at equilibrium. In fact, some systems may be far from
equilibrium and their passive potential changes as a function of homogeneous
reactions. What makes OCP unique is that is a purely electrolytic measurement,
thermodynamically. The experimental parameters to set are the rate (s) and
duration (s).
Using the Internal Resistor
The system contains an internal resistor that is a 1000 Ω resistor. Click or tap the
[+] for the CVS and enable the Use Internal Resistor option. You can engage this
internal resistor to troubleshoot the instrument or to do a demonstration of Ohm's
law as described in our experiment titled "Cyclic Voltammetry Basics: Ohm's
Law". Note: Do not attach an external SPE when using the Internal Resistor.
Cleaning your SPE
While this is not common, you may wish to clean your SPE before running certain
experiments. We recommend running a 2-segment CV with Initial Potential of
1000 mV, Switching Potential 1 of –1000 mV, and Final Potential of 1000 mV.
Set the Sweep Rate to 100 mV/s and Current Range to High. You can choose to
repeat it if you wish. The recommended cleaning solution for most applications is
0.1 M H SO .
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Using the Product with LabQuest App
Preparing your Instrument for Data Collection
1. Insert a screen-printed electrode (SPE) into the SPE connector on the Cyclic
Voltammetry System (see Figure 1). Avoid touching the black electrode part
of the SPE.
2. Fill the scintillation vial about halfway full (~10 mL) with your sample. Insert
the scintillation vial into the clip on the stand. Carefully guide the Cyclic
Voltammetry System with the SPE attached downward into the vial and snap
the instrument into place, as shown in Figure 2.
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Figure 1