Differential Pulse Stripping Voltammetry

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Differential Pulse Stripping Voltammetry

Description

Differential Pulse Stripping Voltammetry (DPS) is an extension of the Differential Pulse Voltammetry technique. It works identically to Differential Pulse Voltammetry except it includes an “accumulation” step.

 

In the accumulation step, analytes are plated or otherwise accumulated on the electrode. Typically, the accumulation is done for tens or hundreds of seconds. The accumulated material is then removed (stripped) from the electrode quickly. Accumulating analyte on the electrode increases the mass of material available for the electrochemical reaction. Currents are higher, so the level of detection falls dramatically. In some systems, Sampled DC Stripping Voltammetry can achieve sensitivity in the parts-per-trillion (ppt) range.

 

You can plot and analyze the data files from this test with Gamry’s Echem Analyst 2™.

 

Setup Parameters

The setup for Differential Pulse Stripping Voltammetry adds two input parameter to the setup for Differential Pulse Voltammetry - Setup Parameters. These new parameters are Conditioning and Accumulation Time.

 

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The accumulation phase of the test is done at Initial E. In a typical stripping voltammetry test this is a voltage where analytes plate onto the electrode surface. You therefore must choose an Initial E where this will occur.

 

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The accumulation phase must have reproducible transport of the analyte to the electrode surface. We strongly recommend stirring whenever the accumulation time is greater than 3 s. If you do not stir, random vibration in the lab environment will lead to extremely poor run-to-run reproducibility. Most electrochemical cells can be used with a magnetic stirrer and a stir bar in the electrolyte.

 

7 - Differential Pulse Stripping Voltammetry

 

Parameter

Description

Units

Pstat

Select the potentiostat/galvanostat to perform the experiment. Each radio button corresponds to an installed potentiostat. You can select only one potentiostat at a time. Potentiostats that are already in use are marked with an asterisk. They can be selected but cannot be used.

 

Test Identifier

A string that is used as a name. It is written to the data file, so it can be used to identify the data in database or data manipulation programs. The Identifier string defaults to a name derived from the technique's name. While this makes an acceptable curve label, it does not generate a unique descriptive label for a data set. The Identifier string is limited to 80 characters. It can include almost any normally printable character. Numbers, upper- and lower-case letters, and the most common punctuation characters including spaces are valid.

 

Notes...

Enter several lines of text that describe the experiment. A typical use of Notes is to record the experimental conditions for a data set.

 

Notes defaults to an empty string and is limited to 400 characters. It can include all printable characters including numbers, upper- and lower-case letters, and the most common punctuation including spaces. Tab characters are not allowed in the Notes string. Press the Notes button on the right-hand side to open a separate Notes dialog box.

 

Output File

The name of the file in which the output data are written. By default, it is saved in the default file directory.

 

The input can be a simple file name with no path information. In this case the output file is located in the default file directory. The default file directory is specified in the Gamry.INI file under the [Framework] section with a Key named DataDir. The default path can be changed using the Path command in the Options menu. It can also include path information, such as C:\MY GAMRY DATA\YOURDATA.DTA. In this example, the data are written to the YOURDATA.DTA file in the MY GAMRY DATA directory on drive C. The default value of the Output File parameter is an abbreviation of the technique name with a *.DTA filename extension. We recommend that you use a *.DTA file name extension for your data file names. The data analysis package assumes that all data files have *.DTA extensions.

 

If the script is unable to open the file, an error message box, Unable to Open File, is generated. Common causes for this type of problem include:

•Invalid file name.

•The file is already open under a different Windows® application.

•The disk is full.

 

After you click the OK button in the error box, the script returns to the Setup where you can re-enter the file name.

 

Initial E

The starting potential of the scan segment. This potential is specified versus the reference electrode potential (vs. Eref).

volts (V)

Final E

The final potential of the scan segment. This potential is specified versus the reference electrode potential (vs. Eref).

volts (V)

Step Size
Differential Pulse Voltammetry - single step

mV

Pulse Size E

mV

Sample Period

seconds (s)

Pulse Time

seconds (s)

Noise Rejection

Specify how a measurement is taken. When Noise Rejection is off, a single point is taken for the measurement. When Noise Rejection is on, data points are taken and averaged for the duration of a line cycle. The line cycle is either 50 or 60 Hz. The speed at which data acquisition is taken varies based on the instrument used. PC5 family potentiostats take data at a rate of 33.333 µs/sample.

 

I/E Range Mode

Select the current range mode and choose between Auto mode or Fixed mode.

 

If set to Auto mode, the I/E Range changes depending on the measured current to optimize the current resolution/error. Auto-ranging does not work well for very small currents or faster sample periods. Do not use Auto mode with sample periods faster than ~1 s.

 

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We recommend Fixed mode, which sets the I/E Range based on the specified Max Current.

 

Max Current

Max Current controls the current measurement range if I/E Range is set to Fixed mode. If I/E Range is set to Auto mode, Max Current specifies the maximum expected starting current.

 

The software adjusts the current range based on the Max Current input. In order to use the most sensitive range that will not overload, the software chooses the current range based on a value that is 89% of the full-scale current range.

 

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The Max Current parameter is a current, not a current density.

 

If your current data look very choppy and stepped, the problem could be a poorly selected current range. If you enter a Max Current value of 10 mA and the maximum current in your sweep is only 100 mA, you are only using 1/100th of the potentiostat's A/D converter range. The result is a significant quantization error. Rerun the test entering a smaller Max Current value.

 

If your current data show perfectly flat and horizontal regions, the current has most likely overloaded the potentiostat's current-measurement circuits. Check that the value that you entered for the Max Current parameter is larger than the actual measured cell current. Try rerunning the test with a larger value for the Max Current.

mA

Electrode Area

The surface area of the sample that is exposed to the solution. The software uses the sample area to calculate the current density and corrosion rate (if applicable). If you do not want to enter an area, we recommend that you leave it at the default value of 1.00 cm².

 

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Do not enter a value of zero!

cm2

Conditioning

You may condition the electrode as the first step of the experiment, e.g., to remove an oxide film from the electrode or to grow one. Conditioning ensures that the metal sample has a known surface state at the start of the experiment. This step is done potentiostatically for a set amount of time.

 

Turn the conditioning phase On or Off with the Conditioning switch check box. Conditioning E is the potential applied during the conditioning phase of the experimental sequence. The conditioning potential has an allowed range of ±8 V. The resolution is 0.25 mV. If you have iR-compensation enabled for the data acquisition phase of your experiment, it is also turned on during conditioning. Conditioning E is always specified vs. Eref, because the open-circuit potential is not measured until after Conditioning is completed.

 

The Conditioning Time is the length of time that the sample is potentiostatted at Conditioning E. The minimum time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

seconds (s), volts (V)

Accum. Time

The potential of the working electrode is maintained at the Initial E for the specified time.

seconds (s)

Equil. Time

The duration during which the cell remains at the initial potential, with the cell turned on before data acquisition begins. It allows the system to equilibrate before the actual experiment starts. No data are recorded during this step.

 

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The input parameter must be an integer. If equilibration is not required, set this value to 0.

seconds (s)

IRComp

Choose the type of iR-compensation to be used during data acquisition. There are two settings:

•None: No iR-compensation is performed.

•PF: Positive-feedback iR-compensation takes a user-entered correction value (PF Corr.) which corrects for the uncompensated resistance. Because this value is entered at the beginning of the experiment and not measured after every point, this compensation method is suitable for fast experiments.

 

PF Corr.

The resistance compensated for with positive feedback (PF) selected under IRComp. This value should be between 80–95% of the uncompensated resistance Ru. You cannot compensate for 100% with PF IRComp enabled.

ohm

Advanced Pstat Setup

The Advanced Pstat Setup checkbox, if checked, opens the Hardware Settings window, to control specific aspects about your hardware. If you are not an advanced user or simply wish to use the default hardware settings as specified in the scripts, just un-check this box. If you wish to specifically set some hardware items, check this box. The Hardware Settings window opens upon clicking the OK button.

 

Electrode Setup

The Electrode Setup checkbox, if checked, opens the Electrode Setup window, to control specific aspects about your electrode. If you are not an advanced user, or simply wish to use the default electrode settings, just un-check this box. If you need to specifically set the electrode type, the stir/purge conditions, or some hardware items, check this box. The Electrode Setup window opens upon clicking the OK button.