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BAS 100B/W Instruction Manual

Electrochemical workstation
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BAS 100B/W Version 2.3
March 2001
MF-9094
INSTRUCTION MANUAL
Electrochemical Workstation
B i o a n a l y t i c a l
S y s t e m s , I n c
2701 Kent Avenue
W e s t L a f a y e t t e
I n d i a n a 4 7 9 0 6

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  • Page 1 BAS 100B/W Version 2.3 March 2001 MF-9094 INSTRUCTION MANUAL Electrochemical Workstation B i o a n a l y t i c a l S y s t e m s , I n c 2701 Kent Avenue W e s t L a f a y e t t e...
  • Page 2 Use for this purpose and accountability for the same rests entirely with the user. The BAS logo is a registered trademark of Bioanalytical Systems, Inc. MS-DOS and Windows are registered trademarks of Microsoft Corporation.

  • Page 3: Table Of Contents

    1. INTRODUCTION........................... 1-1 2. INSTALLATION ............................ 2-1 2.1 INSTALLATION OF THE BAS 100B ELECTROCHEMICAL ANALYZER........2-1 2.2 INSTALLATION OF CPU BOARD FOR BAS 100B/W UPGRADE..........2-9 2.3 INSTALLATION OF REPLACEMENT ROMS IN THE BAS 100B/W..........2-10 2.4 PERSONAL COMPUTER (PC) INSTALLATION................2-11 3.
  • Page 4 6. MATH MENU ............................6-1 6.1 OPERATORS ............................6-1 6.2 SMOOTH ..............................6-1 6.3 DERIVATIVE/INTEGRAL ........................6-3 6.4 CONVOLUTION............................ 6-4 6.5 BACKGROUND............................. 6-5 6.6 AVERAGE.............................. 6-5 7. ANALYSIS............................... 7-1 7.1 RESULTS GRAPH..........................7-1 7.2 RESULTS OPTIONS..........................7-7 7.3 CALIBRATION............................7-9 7.4 STANDARD ADDITION ........................

  • Page 5: Introduction

    1. Introduction This is the Operation Manual for the BAS 100B/W Electrochemical Workstation. It is the fourth generation of a microprocessor-based Electrochemical Analyzer series that started in 1983. The BAS 100B/W uses the latest advances in Personal Computer (PC) technology to increase the efficiency and versatility of the user interface. The MS Windows interface allows instrument control and data storage and processing, together with data presentation on the PC monitor, laser printer or digital plotter.
  • Page 6 Differential Pulse Stripping Voltammetry Linear Sweep Stripping Voltammetry Osteryoung Square Wave Stripping Voltammetry Time Base Amperometric Differential Pulse Triple Pulse Miscellaneous Bulk Electrolysis with Coulometry Electrocapillary Curve Impedance Programmable Potential Wave Form Table 1-1. Electrochemical repertoire of the BAS 100B/W.
  • Page 7 192 KB 116 KB Video RAM 6 KB Cell stand port Custom port for control of BAS Cell Stands and Controlled Growth Mercury Electrode Accessories port Custom parallel port for control of BAS Modules and other accessories Data link port...
  • Page 8 Potentiostat ±12 volts minimum Output compliance voltage Applied voltage range -3.276 volts to +3.276 volts Minimum potential step size 100 microvolts ±2.5 millivolts Absolute accuracy Reference input impedance >10 ohms Maximum output current 190 milliamperes Risetime <2 microseconds Slew rate 10 Volts/microsecond minimum Stability 500 microvolts/day...
  • Page 9 2. Retain the container, packing material and damaged goods until the examining agent has made an inspection report. In all of the above cases, do not return damaged goods to BAS without first contacting our customer service personnel for a Return Authorization Number...
  • Page 10 (by our option) by return of the item to our factory, or shipment of a repaired or replacement part. BAS will not be obliged, however, to replace or repair any piece of equipment that has been abused, improperly installed, altered, damaged or repaired by others.
  • Page 11 Warranty Card Each BAS analyzer system is shipped with a warranty card which should be completed and returned by the end user. This card will enable us to identify and contact the individual responsible for the operation of the instrument. Please return the card as soon as possible so that we may inform you of product updates and other pertinent technical information.

  • Page 12: Installation

    2. Installation The installation of the BAS 100B/W Electrochemical Workstation can be divided into 2 parts: installation of the BAS 100B Electrochemical Analyzer and installation of the Personal Computer (PC). These will be considered in turn. 2.1 Installation of the BAS 100B...
  • Page 13 Figure 2-1. Rear panel of BAS 100B (the ports that are not required for the BAS 100B/W are omitted). VOLTAGE SELECT PCB FUSE FUSE PULL Figure 2-2. Power connector and voltage select.
  • Page 14 Before plugging the Analyzer power cord into a power socket, confirm that the correct voltage has been selected in the power cord connector. This is done as follows: a. Remove the power cord from the power cord connector (the location of this connector is shown in Figure 2-1).
  • Page 15 Analyzer (Figure 2-1) and the other end is attached to the electrodes. This may be a direct connection using the general purpose cable sent with the Analyzer or one for attachment to a cell stand such as the BAS C3 Cell Stand.
  • Page 16 Analyzer (Figure 2-4). Figure 2-4. Attaching cell lead to BAS 100B. There are 3 cell stand configurations available for the BAS 100B/W Workstation (through Setup in the File menu). One configuration (C2) is for the BAS C2 Cell...
  • Page 17 The purging and stirring functions on the BAS C3 Cell Stand can be controlled manually or through the BAS 100B/W. The REMOTE port on the rear of the Cell Stand is connected via a 25 pin ribbon cable to the CELL STAND port on the rear panel of the Analyzer.
  • Page 18 Later versions of the BAS100A and BAS 100B have a jumper on the back panel board to disconnect line 22. However, line 22 is connected on the BAS 100B/W, so the position of the jumper must be switched in order for the knock function of the 303A to operate, 2.
  • Page 19 SMDE or HMDE when the scan is complete. Accessories This port allows the BAS 100B/W to sense and control the accessories and special function modules available to the BAS 100B/W. The accessories that use this custom port are the Low-Current Module, the Power Module/Potentiostat, the Rotating Disk Electrode and the AC Impedance Module.

  • Page 20: Installation Of Cpu Board For Bas 100B/W Upgrade

    A. Analog Board B. I/O Board C. CPU Board a) Remove white plastic board support (item 1). NOTE: early BAS 100A models do not have the board support. b) Loosen four designated screws (Item 2) on card rack and slide card retainer plates outward.

  • Page 21: Installation Of Replacement Roms In The Bas 100B/W

    2.3 Installation of Replacement ROMs in the BAS 100B/W a) Remove the CPU as described in section 2.2 b) Lay CPU board (Figure 2-8) on a flat surface. Components of the CPU board are sensitive to static. Do not lay the board on carpeting, plastic (e.g., bubble wrap), or other surfaces that build up static charge.

  • Page 22: Personal Computer (Pc) Installation

    2.4 Personal Computer (PC) Installation Machine Requirements The BAS Windows software was written for use on BAS PCs. Other IBM compatible PCs may be able to run this software, but there are no guarantees. The MINIMUM requirements for the BAS Windows software are: a) 80386 processor running at 16 MHz, together with a math co-processor.
  • Page 23 Setting up the BAS PC is described in more detail in the enclosed User's Guide. Once the above connections have been made, the system unit and monitor can be powered up.
  • Page 24 Figure 2-10. Install dialog box. 5. The BAS 100W software is opened by double-clicking the BAS 100W icon. Before any operation, it is advisable to check that the communication parameters are correct. These are contained in the Setup dialog box in the File menu (Figure 2-11).
  • Page 25 The knock/dispense routines for the SMDE and CGME modes of the Mercury Electrode are also controlled by the BAS 100B/W, so the Cell Stand option must be set accordingly (the SMDE option can also be used for the PAR 303A SMDE).

  • Page 26: File Menu

    3. File Menu 3.1 File Dialog Box The BAS 100W software uses standard Windows file dialog boxes for transfer of data files between disk drives and the main memory and for other file manipulation. The Load Data File dialog box is shown in Figure 3-1.

  • Page 27: Load Data

    The Load Data command reloads a data file previously saved by the 100W software, in either binary (.BIN) or text (.TXT, .CRL, .SPC and .TAB) format. .TXT files from earlier BAS File Service programs can also be loaded. 3.3 List Data The List Data command lists the data currently in main memory.

  • Page 28: Convert Files

    3.6 Convert Files Convert Files is used to convert data files between the binary (.BIN) and text (.TXT, .CRL, .SPC and .TAB) formats. Up to 100 files can be selected. After the file(s) have been selected, the program prompts you to confirm the number of files. The text format is determined by the Text Data Format dialog box (3.10).
  • Page 29 Mercury Electrode (CGME). The knock/dispense routines for the SMDE and CGME modes of the Mercury electrode are also controlled by the BAS 100B/W, so the Cell Stand option must be set accordingly (the SMDE option can also be used for the PAR 303A SMDE).

  • Page 30: Text Data Format

    Oxidation Current This specifies the sign of an oxidation current - positive Polarity (IUPAC convention) or negative (classical convention). 3.10 Text Data Format When data are listed on the screen, or saved in a text format, each data point includes an X value (typically potential or time), and one or more Y values (typically current or charge).

  • Page 31: Method Menu

    4.2 Select Mode There are 38 Techniques available on the BAS 100B/W, which are divided into 9 Categories. When a given Category is highlighted, the modes associated with that Category are displayed in the Technique list box (Figure 4-1). The required technique can then be selected.

  • Page 32: General/Specific Parameters

    4.3 General/Specific Parameters Some electrochemical techniques require many different parameters, and this can cause confusion. For ease of operation, the parameters are divided into two categories, General and Specific. General Parameters must be set by the user for each experiment, as there are no standard values for these parameters.

  • Page 33: Filter

    Analog filtering is used during data acquisition to lower the output noise. The analog filtering in the BAS 100B/W is a two stage network (Figure 4-4). The first stage is an RC filter, which is followed by a Bessel filter. The filtering characteristics of each stage can be varied, and are related to the time scale of the technique being used.

  • Page 34: Deposit Options

    4.6 Deposit Options Deposit Options is used to define the deposition potential for stripping experiments. The default for this parameter is the initial potential for the potential scan (Initial E). If some other potential is required, then the Deposit E option should be selected, and the required potential should be entered in the Deposit E field (Figure 4-5).

  • Page 35: Hydrodynamic Modulation

    4.9 Controlled Growth This specifies drop growth parameters for the CGME mode of the BAS Controlled Growth Mercury Electrode for both pulse and stripping experiments (Figure 4-8). The CGME mode must be selected for the Cell Stand options in the Setup dialog box for this item to be activated.
  • Page 36 Figure 4-8. Controlled Growth dialog box. The CGME can also be used as a DME when in the CGME mode by activating the Controlled DME check box. This will open the valve at the start of the experiment and close it at the end of the experiment. The mercury will flow freely during the course of the experiment and the Dropping Time (i.e., the time between activations of the drop knocker) is selected using Specific Parameters (the natural drop time at low potentials in aqueous solution for the standard 150 µm capillary is typically...

  • Page 37: Control Menu

    5. Control Menu 5.1 Start Run This command (or F2) initiates the experiment. During runs, all menus are disabled except the Control commands: Start Run, Hold/Continue Run, Reverse Scan and Stop Run. After completion of the run, the menus are re-enabled according to the present mode and data set.

  • Page 38: Run Options

    5.5 Run Options Figure 5-1. Run Options dialog box. This command allows some automation when running experiments. a) It Runs and the Time Interval between the runs must be specified by the user (Note: the Time Interval is in addition to the time required to transfer the data to disk).

  • Page 39: List Run Data

    On the BAS 100B/W, this is achieved by the iR Compensation command. There are two stages to Auto iR Compensation on the BAS 100B/W (P. He and L.R. Faulkner, Anal. Chem. 58 (1986) 523):...
  • Page 40 Measurement of Uncompensated Resistance In this measurement, the electrochemical cell is considered to be electronically equivalent to an RC circuit; that is, the uncompensated resistance (R ) is in series with the double-layer capacitance (C ) (Figure 5-2). Since a Faradaic impedance is not considered as part of this model, the test potential (Test E) must be at a value at which no Faradaic process occurs.
  • Page 41 measured RC error of R u R u /Ω measured R u /Ω time constant/µs measurement/ % 50.3 100.4 -8.4 -3.3 -1.0 -0.4 +0.3 +0.6 +0.7 -0.7 Table 5-1. Measured resistance and time constant via exponential extrapolation (P. He and L.R. Faulkner, Anal. Chem. 58 (1986) 523). Table 5-1 shows the results of resistance measurements for various dummy cells using exponential extrapolation.
  • Page 42 inserted between the reference and auxiliary electrodes to stabilize the circuit, and the testing is continued until the desired level of compensation is achieved or the Overshoot value is exceeded (if this occurs, the amount of compensation to be used in the experiment is slightly decreased from this value). One way to increase the level of compensation is to increase the Overshoot percentage.

  • Page 43: Measure Rest Potential

    be used for every subsequent run (Note: if Always is chosen, the instrument does not redo the iR Test before every run). c) Before Auto iR Compensation can be used the iR Test must first be run. This test requires three parameters values to be specified by the user: Test E (this must be a potential at which no Faradaic process occurs) Comp.

  • Page 44: Measure Impedance

    5.9 Measure Impedance This command is used to calibrate the BAS 100B/W for impedance experiments (BAS Impedance Module required). This calibration requires a 1000 ohm resistor, which is connected to the working electrode on one side and the reference and auxiliary electrodes on the other.

  • Page 45: Clean Electrode

    gure 5-7. Immediate Purge/Stir dialog box. 5.11 Clean Electrode The Clean command is used to hold the electrode at a fixed potential for a set length of time without accumulating any data. This can be useful for generating clean, reproducible working electrode surfaces. Figure 5-8.

  • Page 46: Cell On/Off

    5.13 Cell On/Off When Cell On is selected, the working electrode is connected at all times. When Cell Off is selected, the working electrode is only connected during experimental runs. For most experiments, the cell should be off between runs, since there is more chance of damaging the instrument (and of personal injury when using the PWR-3) if the cell leads are connected/disconnected when the cell is on.

  • Page 47: Math Menu

    In all data manipulation programs, attempts are made not to bias the signal. The major effect of the programs in the BAS 100W is the elimination of the higher frequency components of the signal, typically 10's of Hz and greater (the...
  • Page 48 The only requirement for the number of points is a block is that this number is odd. Any odd number between 5 and 25 can be chosen on the BAS 100W - the larger the number of points, the greater the smoothing.

  • Page 49: Derivative/Integral

    Figure 6-2. Smooth dialog box. Smoothing Mode Default: Moving Average Point/Cutoff This controls the degree of smoothing (higher Point/lower Cutoff produces greater smoothing). Default: 7 (Point), 20 (Cutoff) Smooth After Run When activated, experimental data automatically smoothed at the end of the experiment.

  • Page 50: Convolution

    In addition to differentiation and integration, semi-differentiation and semi- integration are also commonly used for processing electrochemical data. Both of these processes are available on the BAS 100W as Convolution Mode options (Figure 6-4). Additional smoothing is available for semi-differentiation, since this process can increase the noise level.

  • Page 51: Background

    6.5 Background This command can be used to subtract a voltammogram stored on the hard disk from the voltammogram in the main memory. The data file for subtraction is selected from the Background File dialog box (Figure 6-5) (for a more detailed discussion of file dialog boxes, see the File menu section).

  • Page 52: Analysis

    7. Analysis 7.1 Results Graph The data available from an electrochemical experiment may be peak potentials and currents, half-wave potentials and limiting currents, slopes and intercepts of straight line plots or the amount of charge passed during the experiments. These data can be obtained using the Results Graph.
  • Page 53 (N.B. Due to the finite time required for the potential step to be complete, the data in the first few milliseconds of potential step experiments is often distorted. The BAS 100W Auto option therefore only uses the last 80% of the collected data when calculating slopes and intercepts).
  • Page 54 BASELINE PEAK POTENTIAL PEAK CURRENT PEAKAREA BASELINE PEAK POTENTIAL PEAKAREA PEAK CURRENT Figure 7-1. Peak area for symmetric and tailed curves. Determination of Peak Potentials and Inflection Points NOTE: If there are fewer than 30 points available in a data set of segment, peak finding is not possible and a warning message is shown.
  • Page 55 that a 25 mV potential window is being examined for each ∆I calculated). To ensure that it is a true peak (i.e., not merely noise), two criteria must be met. First, the 3 points (∆I values) on either side of the E window are examined for continuity of sign;...
  • Page 56 a) Symmetric curves - The baseline is the line between the two current minima in the range of E + 250 mV (Figure 73). Figure 7-3. Symmetric current response. b) Tail curves - The baseline is the line between two points on the I vs. E curve 50 mV apart in a range of 250 mV preceding E (Figure 7-4).
  • Page 57 Determination of the Slope and Intercept of an Anson or Cottrell Plot The slope and intercept of the CA Cottrell plot and the CC Anson plot are determined by an unweighted linear least squares fit routine on the last 80% of the data points following both the forward and reverse potential steps (Figure 7-6).

  • Page 58: Results Options

    7.2 Results Options Figure 7-7. Results Options dialog box. Peak Shape This defines the shape of the curve. There are instances when the default peak shape selection is appropriate: example, when using microelectrodes at low scan rates, as this produces a sigmoidal plot for CV.
  • Page 59 HR, and that segment specified for TPTB in Display Data Set (in General Parameters). Method This specifies which option (Auto or Manual) is to be used. Sensitivity Factor This command adjusts the sensitivity of the peak search operation. The height of the smallest detectable peak decreases by a factor of 10 for each stepwise decrease in the Sensitivity Factor.

  • Page 60: Calibration

    7.3 Calibration This command is used to set up a calibration curve for quantitative analysis. First, the Mode must be selected, and the General and Specific Parameters entered. The Analysis Calibration dialog box appears when Calibration is clicked (Figure 7- Figure 7-8.

  • Page 61: Standard Addition

    It should also be noted that the first run number is now 001, not 0 as in previous versions of the BAS 100W software. Figure 7-9. Samples dialog box.
  • Page 62 Since 3-digit run numbers are used in the data filenames, it may be necessary to rename data files before reprocessing. It should also be noted that the first run number is now 001, not 0 as in previous versions of the BAS 100W software. 7-11...

  • Page 63: Graphics Menu

    8. Graphics Menu This Menu is used to display the experimental data after the experimental run and after any post-run data processing. 8.1 Single Graph The Single Graph window displays the experimental data (Figure 8-1). The size and position of this windows can be changed by the user (by dragging the caption or the borders), and are defined initially by the BAS100W.INI file.

  • Page 64: Graph Options

    8.2 Graph Options This dialog box controls the appearance of the graph on the PC screen and on the hard copy (Figure 8-2). All Graph Options are saved in the BAS100W.INI file (except X/Y Freeze and the Min. and Max. values, which typically only apply to a particular data file).
  • Page 65 for the first run are regraphed with auto-scaling, the Min. and Max. values are correct for the present graph. X/Y Titles When activated, the specified text replaces the default labels on the axes. X/Y Size Ratio This defines the fraction of the total windows area that is occupied by the graph Curve Options These control the way the curves are drawn.

  • Page 66: Graph Colors

    The colors of each feature on the graph can be selected (for both the PC screen and the hard copy). These Graph Colors are saved in the BAS 100W.INI file. To change a color, first click the colored check box beside the selected feature; a cross will replace the color and the sample color patch will change to the present color of that feature.

  • Page 67: Print Menu

    9. Print Menu 9.1 Print Graph This command transfers the present graph (Single Graph or Multi-Graph) to the default printer (an alternative printer can be selected using Printer Setup) using the options specified in Print Options. 9.2 Print Options This dialog box contains graph options that pertain only to printed graphs (Figure 9- Figure 9-1.

  • Page 68: Multi-Print Files

    Omit File Names Above This option specifies whether the file name is above Graph the graph both on the monitor and on printed/copied to clipboard graphs. 9.3 Multi-Print Files This command sets up a print queue for data files. Up to 100 files can be selected from the Multi-Print Files dialog box.

  • Page 69: Operation Modes

    10. Operation Modes There are 38 techniques available on the BAS 100B/W. This may appear to be a bewildering number, but many of these techniques are related, or are variations of other techniques. There are a number of broad divisions that can be made.
  • Page 70 Chronocoulometry (CC) Chronoamperometry (CA) Step waveform (STEP) Pulse Techniques (Stationary Solution) Differential Pulse Voltammetry/Polarography (DPV/P) Normal Pulse Voltammetry/Polarography (NPV/P) Sampled Current Polarography (SCP) Square Wave Techniques (Stationary Solution) Barker Square Wave Voltammetry/Polarography (BSWP/V) Osteryoung Square Wave Voltammetry (OSWV) AC Techniques (Stationary Solution) Alternating Current Voltammetry/Polarography (ACV/P) Phase Selective Alternating Current Voltammetry/Polarography (PSACV/P) Second Harmonic Alternating Current Voltammetry/Polarography (SHACV/P)
  • Page 71 There are a number of parameters that are common to all techniques. a) Potential range. When only a single potential is required, this is defined by Initial E. If a potential range is required, this is defined by Initial E and Final E (for single sweep/scan/step experiments), or Initial E, High E and Low E (for two or more sweep/ scans/steps in the experiment).

  • Page 72: Linear Sweep Techniques (Lsv, Cv, Logi, Cycle)

    10.1 Linear Sweep Techniques (LSV, CV, LOGI, CYCLE) In LSV, the potential is varied linearly from an initial potential (Initial E) to a final potential (Final E) at a constant rate (Scan Rate), and the current is monitored as a function of the applied potential.
  • Page 73 separation of the peak potentials is 57/n mV (n = number of electrons transferred per molecule). HIGH INITIAL LOW E SCAN SEGMENTS Figure 10-2. Potential wave form for CV. The peak current for a reversible process is given by the Randles-Sevcik equation: −...
  • Page 74 This is discussed in more detail in section 10.6. It is important to note that the potential wave form used for CV and LSV on the BAS 100B/W (and other digital instruments) is a staircase wave form, since it is impossible to generate digitally a true linear wave form.
  • Page 75 BAS Capsules Adsorption of Reduced Glutathione on a Mercury Surface Determination of Heterogeneous Electron Transfer Rate Constant Electrochemical Conversion of [FeIr (CO) to [FeIr (CO) Identification of the Products of Oxidation of [CpFe(CO) Using Infra- red Spectroelectrochemistry Potentiostatic Measurements of a Tc(III)/Tc(II) Couple Using an OTTLE...
  • Page 76 I jack on the back panel of the BAS 100B. This is used when many CV cycles are required, and the required data storage exceeds the data storage capacity. It can also be used to condition the working electrode.
  • Page 77 2.048 x 10 pulses/s in the BAS 100B/W. The rate of change from the DAC is controlled by allowing only a fraction of the clock pulses to reach the DAC. The allowed Scan Rates (for mV/s) are calculated from the equation shown below and some values are listed in Table 10-1.
  • Page 78 Frequency divider Scan Rate (mV/s) Frequency divider Scan Rate (mV/s) 51200 1024 40960 1019 34166 1014 29257 1009 25600 1004 22755 20480 18618 17066 15753 14628 13653 12800 12047 11378 10799 10240 9752 9309 (1 mV/s resolution) Table 10-1. Some allowed Scan Rates for mV/s. For Scan Rates of V/s, the resolution of the staircse is 1.6 mV.
  • Page 79 The convoluted voltammograms (both semi-derivative and semi-integral) are sometimes reported. The semi-differential voltammogram has symmetric peaks and better resolution than the standard voltammogram (see BAS Capsule 275 and Current Separation article 6. The semi-integral is used to correct for iR drop. 10-11...
  • Page 80 Iout jack on the rear panel of the BAS 100B. If the current is not being recorded, it is advisable to adjust the Sensitivity to 100 mA/V to avoid saturation. If the current is being recorded (e.g., on an XY recorder), the Sensitivity must be...

  • Page 81: Potential Step Techniques (Ca, Cc, Step)

    10.2 Potential Step Techniques (CA, CC, STEP) In these techniques, the potential is stepped from one value to another, and the current (CA) (or charge (CC)) response is monitored as a function of time (it should be remembered that charge is simply the integral of current). After the potential has been held at this value for a time τ, the potential can be stepped to another value (often the original potential).
  • Page 82 (for CC). For diffusion controlled systems, these are straight line plots, and are often referred to as the Cottrell plot (for CA) and the Anson plot (for CC). These plots are available as standard plots on the BAS 100B/W. 10-14...
  • Page 83 Figure 10-6. Chronoamperogram (current-time) response for double-potential-step CA. Figure 10-7. Chronocoulogram (charge-time) response for double-potential-step CC. Therefore, both CA and CC can be used to measure one of n, C, A and D using the gradients of these straight line plots, provided the other three constants are known. However, other techniques (e.g., pulse techniques) have lower detection limits, so CA and CC are generally not used for concentration measurements.
  • Page 84 However, in some instruments, this is not strictly the case, since the charge is obtained by integrating the discrete current values, and some charge is invariably lost. In contrast, in the BAS 100B/W, there is a 'true' charge-to-voltage converter, which means that none of the early information is lost.
  • Page 85 STEP allows a cyclic potential step wave form to be applied to the working electrode. There is no data acquisition in this mode although the response can be rear panel jack of the BAS 100B. The STEP mode is primarily monitored at the I designed for electrode cleaning and conditioning.
  • Page 86 Mode = CA General Parameters Initial E (mV) = 0 -3276 to 3276 High E (mV) = 0 -3276 to 3276 Low E (mV) = 0 -3276 to 3276 Initial Direction = Negative Negative or Positive Pulse width (msec) = 250 1 to 32000 Sensitivity = 1 µA/V 100 mA/V to 100 nA/V (10 pA/V with the...
  • Page 87 Comments The maximum data file length is 1000 points/step. The circuitry for CC is a direct charge-to-voltage converter. The integrating capacitor that is used to accumulate the charge in the 10 µC/V Sensitivity range is automatically discharged and reset to zero when it nears the voltage saturation level. This operation allows a much greater charge to be measured during the experiment.
  • Page 88 Mode = STEP General Parameters Initial E (mV) = 0 -3276 to 3276 High E (mV) = 0 -3276 to 3276 Low E (mV) = 0 -3276 to 3276 Initial Direction = Negative Negative or Positive Pulse width (msec) = 250 1 to 32000 Number of Cycles = 1 0 to 65535...

  • Page 89: Pulse Techniques (Scp, Npv/P, Dpv/P)

    Dropping Time applies to polarography experiments, in which the potential pulse, current sampling and renewal of the mercury drop are coordinated (this is controlled by the BAS 100B/W). As discussed above, the current is sampled at the end of the pulse, and the mercury drop is knocked off at the end of the Sample Width (which coincides with the end of the pulse).
  • Page 90 Sampled Current Polarography (SCP) or Tast polarography is a modification of the classical D.C. polarography experiment, and was designed to reduce the effect the changing surface area of the mercury drop. The potential wave form is shown in Figure 10-10. The potential is varied in a series of steps (it is held at each step for the Drop Time), and the current is sampled at the end of each drop.
  • Page 91 The sensitivity and detection limit of SCP are similar to those of DC polarography (5 µA/mM and 10 M). The major advantage of SCP over D.C. polarography is the smoothed current output, which facilitates measurement of the half-wave potentials and limiting currents. Although this is a essentially a polarographic technique, it can be used as a slow scan rate voltammetry technique.
  • Page 92 reaction of interest occurs at the diffusion limited rate. This technique is useful for discriminating between a reversible redox process (rapid electron transfer) and an irreversible redox process (slow electron transfer on the reverse step), since both can be detected by NPV/P, whereas only the reversible process can be detected by RPV/P.
  • Page 93 reduction. At potentials well positive of the redox potential, there is no faradaic reaction is response to the pulse, so the differential current is zero. At potentials around the redox potential, the differential current reaches a maximum and decreases to zero as the current becomes diffusion-controlled. The current response is therefore a symmetric peak (Figure 10-15).
  • Page 94 Graphics Menu Single Graph displays the current vs. potential plot. Analysis Menu The Auto option for Results Graph displays the current vs. potential plot, and the half-wave potential and limiting current are listed in the Main window. Alternative baselines can be set by the user through the Manual option.
  • Page 95 Analysis Menu The Auto option for Results Graph displays the current vs. potential plot, and the half-wave potential and limiting current are listed in the Main window. Alternative baselines can be set by the user through the Manual option. Mode = DPV/P General Parameters Initial E (mV) = 0 -3276 to 3276...
  • Page 96 Analysis Menu The Auto option for Results Graph displays the current vs. potential plot, and the peak potential and peak current are listed in the Main window. Alternative baselines can be set by the user through the Manual option. 10-28...

  • Page 97: Square Wave Techniques (Oswv, Bswv/P)

    The chief advantages are the greater sensitivity and the faster speed (for OSWV). There are two different square wave potential wave forms available on the BAS 100B/W, Osteryoung (OSWV) and Barker (BSWV/P). These are shown in Figure 10-16 and Figure 10-17.
  • Page 98 The potential wave form for OSWV consists of a square wave superimposed on a staircase wave form. It can also be viewed as a series of pulses alternating in direction (hence, the relation to both pulse and A.C. techniques). The current is sampled at the end of each of the pulses (or half-cycles).
  • Page 99 The other advantage of OSWV compared to DPV/P is its speed. Scan rates of up to 80 V/s are available on the BAS 100B/W, although scan rates of 100s mV/s to a few V/s are typically used (note that the scan rate for OSWV depends on the square wave frequency).
  • Page 100 Graphics Menu Single Graph displays the current vs. potential plot(s) of the Data Sets specified in the Graph and Results Options dialog boxes. Analysis Menu The Auto option for Results Graph displays the current vs. potential plot(s) of the Data Sets specified in the Graph and Results Options dialog boxes, and the peak potential and peak current are listed in the Main window.
  • Page 101 Analysis Menu The Auto option for Results Graph displays the difference current vs. potential plot, and the peak potential and peak current are listed in the Main window. Alternative baselines can be set by the user through the Manual option. 10-33...

  • Page 102: Techniques (Acv/P, Psacv/P, Shacp/V, Tacv/P, Dtacv/P)

    10.5 A.C. Techniques (ACV/P, PSACV/P, SHACP/V, TACV/P, DTACV/P) Sinusoidal A.C. Techniques (ACV/P, PSACV/P, SHACV/P) There are essentially two categories of sinusoidal A.C. techniques. In A.C. Impedance, the D.C. potential is held constant (e.g., at the redox potential) and a small amplitude A.C. potential is applied. This is discussed in more detail in section 10.9.4.
  • Page 103 Figure 10-21. A.C. current response for ACV/P. The phase angle for an ideal reversible system is 45 , whereas for quasi-reversible systems (slow electron transfer), it is less than 45 . Since reversibility depends on the timescale of the experiment, increasing the A.C. frequency often causes the behavior of a system to change from reversible to quasi-reversible.
  • Page 104 measure the redox potentials of species that react rapidly when electrolyzed. A typical current response for SHACV/P is shown in Figure 10-22. Figure 10-22. Second harmonic A.C. current response for SHACV/P. General Parameters for ACV/P, PSACV/P, SHACV/P Initial E (mV) = 0 -3276 to 3276 Final E (mV) = 0 -3276 to 3276...
  • Page 105 d) The sample interval is equal to the product of the Scan Rate and the Drop Time (or Step Period) (e.g., the default value is 6 mV.) Graphics Menu Single Graph displays the appropriate current vs. potential plot for all the techniques.
  • Page 106 Figure 10-24. A.C. current response for TACV/P. In TACV/P, the current is sampled at the end of each half-cycle. One variation of TACV/P is DTACV/P (D = Differential), in which a different current sampling routineis used in order to eliminate the charging current (Figure 10-25 and Figure 10- 26).
  • Page 107 Figure 10-26. A.C. current response for DTACV/P. General Parameters for TACV/P, DTACV/P Initial E (mV) = 0 -3276 to 3276 Final E (mV) = 0 -3276 to 3276 Sensitivity = 1µA/V 100 mA/V to 100 nA/V (10 pA/V with the Low Current Module) Specific Parameters for TACV/P, DTACV/P Scan Rate (mV/sec) = 4...
  • Page 108 Analysis Menu The Auto option for Results Graph displays the current vs. potential plot, and the peak potential and peak current are listed in the Main window. Alternative baselines can be set by the user through the Manual option. 10-40...

  • Page 109: Stripping Techniques (Bswsv, Dpsv, Lssv, Oswsv)

    10.6 Stripping Techniques (BSWSV, DPSV, LSSV, OSWSV) Stripping voltammetry is a very sensitive method for analysis of trace amounts of electroactive species in solution. Detection limits for metal ions at sub-ppb levels have been reported. There are 3 important parts in a stripping experiment. These are: a) Deposition b) Quiet Time c) Stripping...
  • Page 110 BSWSV). Of these 4 options, DPSV and OSWSV are most often used, due to their good sensitivity and low detection limits, together with their speed of operation. A typical current response for the stripping step for OSWSV is shown in Figure 10-27. Figure 10-27.
  • Page 111 ASV. References Stripping Voltammetry, A.W. Bott, Curr. Seps. 12 (1993) 141. BAS Capsule No. 150 Anodic Stripping Voltammetry of Lead and Cadmium An Inexpensive Approach to Inorganic Gunshot Residue Analysis using Anodic Stripping Voltammetry.
  • Page 112 Deposit Options for BSWSV, DPSV, LSSV and OSWSV The Deposit Options dialog box in the Method Menu is used to control the Deposition Potential. The default for this parameter is the initial potential for the potential scan (Initial E). However, if some other potential is required for the Deposition Potential, then the Deposit E option should be selected.
  • Page 113 Specific Parameters Scan Rate (mV/sec) = 20 (4) 1 to 200 Pulse Amplitude (mV) = 50 -250 to 250 Sample Width (msec) = 17 1 to 250 Pulse Width (msec) = 50 3 to 2000 Pulse Period (msec) = 200 40 to 8000 Quiet Time (sec) = 10 0 to 65535...
  • Page 114 Specific Parameters Sample Interval (mV) = 1 1 to 20 Quiet Time (sec) = 10 0 to 65535 Mode = OSWSV General Parameters Initial E (mV) = 0 -3276 to 3276 Final E (mV) = 0 -3276 to 3276 Rotation Rate (rpm) = 400 1 to 10000 Sensitivity = 1µA/V 100 mA/V to 10 pA/V...
  • Page 115 Analysis Menu The Auto option for Results Graph displays the current vs. potential plot for the stripping step, and the peak potential and peak current are listed in the Main window (it should be noted that the default Peak Shape for all the stripping techniques is Symmetric).

  • Page 116: Hydrodynamic Techniques (Rde, Hdm)

    10.7 Hydrodynamic Techniques (RDE, HDM) The current response to an applied potential may be determined by a number of parameters. Two of the most important are the rate of electron transfer and the rate of mass transport from the bulk solution to the surface of the working electrode. The rate of electron transfer can be controlled by the applied potential, and is not discussed further.
  • Page 117 The basic Rotating Disk Electrode experiment discussed above is carried out on the BAS 100W using the RDE mode. Typical potential and rotation rate waveform are shown in Figure 10-28, and a typical current response is shown in Figure 10-29. The limits for the rotation rate are 0 rpm to 10000 rpm (although in practice the lowest reasonable rotation rate is about 100 rpm).
  • Page 118 FINAL QUIET TIME INIT Figure 10-28. Typical rotation rate (A) and potential wave form (B) for RDE. Figure 10-29. Typical current response for RDE. Hydrodynamic Modulation (HDM) is a related technique in which the frequency is varied sinusoidally with time. More specifically, ω is varied, since i is proportional to ω...
  • Page 119 Figure 10-30. The modulated rotation rate used for HDM. Current ∆i i ω Figure 10-31. A.C. current output for HDM. Figure 10-32. Typical current response for HDM. ∆i only depends on the rate of mass transport to the working electrode, so there is no contribution from charging current, oxidation or reduction of the electrode or adsorbed species or electrolyte/solvent.
  • Page 120 Mode = RDE General Parameters Initial E (mV) = 0 -3276 to 3276 Final E (mV) = 0 -3276 to 3276 Scan rate = 20 mV/s 1 to 51200 (µV/s) 1 to 51200 (mV/s) 1 to 300 (V/s) Rotation Rate (rpm) = 400 0 to 10000 Sensitivity = 1 µA/V 100 mA/V to 100 nA/V (10 pA/V with the...
  • Page 121 Figure 10-33. Hydrodynamic Modulation dialog box. Data Processing This specifies the method for handling the A.C. current output - Lock-in or Rectify. Rotate during Quiet Time A finite length of time is required for the Rotating Disk Electrode to reach the selected rotation rate.

  • Page 122: Time Base Techniques

    Generally, such techniques are used for amperometric titrations, amperometric sensors, flow cells, etc. The variation between the three techniques available on the BAS 100B/W is the potential wave forms used; that is, the potential wave forms have been modified to improve selectivity.
  • Page 123 One modification of the TB potential wave form is to superimpose a sequence of pulses of constant amplitude (Figure 10-36). This is the Differential Pulse (DPTB) technique. As the current is sampled just before the pulse and at the end of the pulse, there is effective discrimination against the background current.
  • Page 124 examined later). For detection of sugars, the pulse sequence is as follows: the first pulse cleans the electrode surface and deposits an oxide layer on the surface, the second pulse reactivates the electrode surface by removing the oxide layer and adsorption of the analyte occurs, and detection occurs on the third pulse.
  • Page 125 Sensitivity = 1 µA/V 100 mA/V to 100 nA/V (10 pA/V with the Low Current Module) Specific Parameters Real Time Integrator = Off Off/On Quiet Time (sec) = 2 0 to 65535 Comments a) The Sample Interval is the time resolution of the experiment. b) The number of data points recorded in an experiment must be less than or equal to 8000, which is the data storage limit.
  • Page 126 Comments a) Pulse Width is the duration of the potential pulse. b) Sample Width is the time at the end of the pulse during which the current is measured. The maximum value is Pulse Width - 5 msec. The current is sampled 16 times per msec.
  • Page 127 c) Sample Width is the time at the end of the pulse during which the current is measured. This parameter cannot have a value greater than half the Pulse Width. d) Increment E is the incremental change in the potential following each triple pulse cycle.

  • Page 128: Miscellaneous Techniques (Be, Ecm, Hr, Imp)

    10.9 Miscellaneous Techniques (BE, ECM, HR, IMP) 10.9.1 Bulk Electrolysis with Coulometry (BE) The principle behind the Bulk Electrolysis (BE) experiment is very simple. If only the oxidized species is initially present, then the potential is set at a value sufficiently negative to cause rapid reduction and is maintained at this value until only the reduced species is present in solution.
  • Page 129 screen. The ratio of the average current during the time interval just passed to that of the first time interval is also shown. This ratio is an important criterion for determining the extent of the electrolysis; that is, electrolysis is generally complete when this ratio reaches 1% (any residual current being background current).
  • Page 130 Another potential source for error in the charge measurement is the use of automatic Sensitivity control, since about 3 msec is required for this measurement, during which time no measurement can be taken. This error is only significant if the time constant of the cell is short.

  • Page 131: Electrocapillary Measurement (Ecm)

    10 drops. As well as being tedious and time-consuming, it is prone to human error. On the BAS 100B/W, the curve measurement is automated. The measurement of the drop lifetime, the variation in potential and the plot of the electrocapillary curve are controlled by the microprocessor.
  • Page 132 6.4 mV 1msec (1KHz) POTENTIAL INTERVAL Figure 10-42. Potential wave form for ECM. The sampling time is 1 msec and the time required for the decision algorithm is 2 msec; that is, the time resolution is 3 msec. Once drop has been detected, the system remains at the same potential (for multiple drop measurements) or it calculates and sets the next applied potential.
  • Page 133 b) Drop Ratio is a binary exponent, which is used as a criterion to determine drop fall. For drop fall to be detected, the current value x 2 must be less than the previous current value. Graphics Menu Single Graph displays the electrocapillary curve. Analysis Menu The Auto option for Results Graph displays the electrocapillary curve, and the t...

  • Page 134: Hold-Ramp-Step (Hr)

    10.9.3 Hold-Ramp-Step (HR) HR allows the programming of up to 12 time and/or potential based segments. It is used to build custom waveforms for special applications. Odd-numbered segments are chronoamperometric (current vs. time at a fixed potential) and even-numbered segments are voltammetric (current vs. applied potential ramp).

  • Page 135: Impedance (Imp)

    The range of frequencies available on the BAS 100W is 0.1 mHz to 1 kHz (i.e., the timescales that can be detected are between 10000 sec and 1 msec).
  • Page 136 θ (the phase angle) is shown in Figure 10-44. It should also be noted that these parameters vary with frequency (ω). Figure 10-44. Vector diagram for impedances. There are 14 impedance plots available on the BAS 100B/W. These are as follows: 1. -Z" - Z' (Nyquist plot) 2. -Y" - Y' 3.
  • Page 137 12. Z' - Z"/ω 13. -Z" & Z' - 1/Sqrt(ω) 14. Cot θ - Sqrt(ω) One of the most difficult aspects of impedance measurements is the interpretation of the experimental data. The basic approach is that components of the electrochemical cells can be modeled as components of an electronic circuit.
  • Page 138 Module is used in conjunction with the Faraday cage, which shields the cell from electronic interferences. Before any IMP experiments can be run, the BAS 100B/W must be calibrated. This is done using Measure Impedance in the Control Menu. This calibration requires a 1000 ohm resistor, which is connected to the working electrode on one side and the reference and auxiliary electrodes on the other.
  • Page 139 Mode = IMP General Parameters Initial E (mV) = 0 -3276 to 3276 Low Frequency (Hz) = 1E 1 -4 to 2 High Frequency (Hz) = 1E 3 -2 to 3 A.C. Amplitude (mV) = 5 1 to 250 Auto, 100 mA/V to 1 µA/V Sensitivity = Auto Specific Parameters Freq.

  • Page 140: Service And Troubleshooting

    The filter is not removable for cleaning, but can be easily cleaned with a vacuum cleaner equipped with a brush accessory. Be sure that the BAS 100B power switch is off before cleaning so that the internal fans do not pull in dust that is dislodged during filter cleaning.

  • Page 141: Reference Electrodes

    A poor reference electrode can cause considerable problems, so these should be carefully maintained. BAS Ag/AgCl electrodes are shipped with the Vycor frit covered by yellow plastic. This should be removed upon receipt, and the electrode should be stored with the Vycor frit immersed in a solution of 3M NaCl, where it should remain when not in use.
  • Page 142 Symptom Possible Cause Corrective Action When BAS 100B is turned-on, fans do not run Not plugged in Plug in! Blown fuse Replace fuse Defective power cord Replace cord Defective power switch Replace switch Defective fans Replace fans Defective power Check power supply...
  • Page 143 General Protection Fault Restart BAS 100W software BAS 100B doesn’t respond to PC commands Run Self-Test Hardware “Linked Failed” error message Reset BAS 100B or restart BAS 100W software 11-4...

  • Page 144: Removal Of Circuit Boards

    B. I/O Board C. CPU Board a) Remove white plastic board support (item 1). NOTE: early BAS 100A models do not have the board support. b) Loosen four designated screws (Item 2) on card rack and slide card retainer plates outward.

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