1. DL manuals
  2. BAS
  3. Laboratory Equipment
  4. 100B/W
  5. Instruction Manual

BAS 100B/W Instruction Manual

Manual is about: Electrochemical Workstation

Summary of 100B/W

  • Page 1

    Bas 100b/w version 2.3 march 2001 mf-9094 instruction manual b i o a n a l y t i c a l s y s t e m s , i n c 2 7 0 1 k e n t a v e n u e 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 electrochemical workstation.

  • Page 2

    Manufacturer’s note this instrument, either wholly or in part, is manufactured for research purposes only. Use for medical diagnosis is not intended, implied or recommended by the manufacturer. Use for this purpose and accountability for the same rests entirely with the user. The bas logo is a regis...

  • Page 3

    1. Introduction................................................................................................................................... 1-1 2. Installation .................................................................................................................................... ...

  • Page 4

    6. Math menu ......................................................................................................................................... 6-1 6.1 operators ......................................................................................................................................

  • Page 5: Introduction

    1-1 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 ef...

  • Page 6

    1-2 sweep techniques linear sweep voltammetry with linear and log output cyclic voltammetry step techniques chronoamperometry chronocoulometry pulse techniques differential pulse voltammetry and polarography normal pulse voltammetry and polarography sampled current polarography square wave technique...

  • Page 7

    1-3 features • thirty-eight techniques • pc control through windows interface • interaction with other windows applications • point & click user interaction • high resolution graphics • 100 µ v potentiostat resolution • true charge to voltage converter for chronocoulometry • hardware interfaces with...

  • Page 8

    1-4 potentiostat output compliance voltage ± 12 volts minimum applied voltage range -3.276 volts to +3.276 volts minimum potential step size 100 microvolts absolute accuracy ± 2.5 millivolts reference input impedance >10 11 ohms maximum output current 190 milliamperes risetime slew rate 10 volts/mic...

  • Page 9

    1-5 minimum personal computer requirements processors 80386, 16 mhz 80387, 16 mhz memory 2 mb ram hard drive 80 mb floppy drives 1.2 mb 5.25” 1.44 mb 3.5” ports 2 serial 1 parallel mouse ps/2 monitor 14” color vga unpacking and inspection carefully unpack the bas 100b/w from the shipping containers....

  • Page 10

    1-6 (ra#). When a defective part is returned to bas, the ra number immediately identifies you as the sender and describes the item being returned. To avoid confusion, bas refuses all unauthorized return shipments. Product warranty bioanalytical systems, inc. (bas) warrants equipment by the company t...

  • Page 11

    1-7 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 ma...

  • Page 12: Installation

    2-1 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 electrochemical ana...

  • Page 13

    2-2 figure 2-1. Rear panel of bas 100b (the ports that are not required for the bas 100b/w are omitted). Fuse pull fuse voltage select pcb figure 2-2. Power connector and voltage select..

  • Page 14

    2-3 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). B. Slide the plast...

  • Page 15

    2-4 b. Slide the plastic window to the left to expose the voltage select printed circuit card (this card is shown in figure 2-2). The orientation of this card in the connector determines the voltage option. C. If the number printed on the outer edge of the board does not correspond to the available ...

  • Page 16

    2-5 reference (white) auxiliary (red) working (black) to cell connector on bas 100a strain relief ground (black) figure 2-3. Cell (electrode) end of cell cable. A plastic mounting lug near the end of the cell cable provides strain relief by preventing movement of the line or cell. Cell stand connect...

  • Page 17

    2-6 stands, and the other two are for the bas controlled growth mercury electrode (cgme) - one for the smde mode (smde) and one for the cgme mode (cgme). The smde configuration can also be used with the parc 303a smde. Bas c2/c3 cell stand the purging and stirring functions on the bas c3 cell stand ...

  • Page 18

    2-7 parc model 303a smde the jumper on the back panel board (figure 2-6) must be in the disconnected position for the parc 303a. The bas 100b/w can be used to control the stirring, purging, knock and dispense of the parc 303a smde. Two connections are required (figure 2-6): to cell stand connector o...

  • Page 19

    2-8 white pin into the ref electrode socket electrocapillary measurements can be done using the 303a, but only with manual control; that is, toggle the drop function switch to the dme position just before the start of the experiment and toggle to either smde or hmde when the scan is complete. Access...

  • Page 20: 2.2

    2-9 2.2 installation of cpu board for bas 100b/w upgrade b a c 2 4 1 3 4 2 pc boards 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 c...

  • Page 21: 2.3

    2-10 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...

  • Page 22: 2.4

    2-11 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 ...

  • Page 23

    2-12 e) serial interface connectors (com1 and com2). These can be used for any serial rs232c device; for the bas 100b/w, they are used for communication with the electrochemical analyzer and for plotting. Com1 is connected with the data link port on the rear panel of the analyzer, and com2 is connec...

  • Page 24

    2-13 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). Figure 2-11. Setup ...

  • Page 25

    2-14 cell stand the bas 100b/w can control the purging and stirring for bas cell stands and the bas controlled growth 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...

  • Page 26: File Menu

    3-1 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. Figure 3-1. File dialog box. File name this fie...

  • Page 27: 3.2

    3-2 directories list the current pathname is shown above this list box, and is updated when a different disk drive or directory is selected. The path is changed by selecting one of the directories shown in this list and then clicking [ok] or pressing enter> (alternatively, you can double-click on th...

  • Page 28: 3.6

    3-3 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 th...

  • Page 29

    3-4 com port this specifies which pc communications port is connected to the bas 100b. A value of 0 disables the communication. Baud rate this specifies the rate at which information is transferred between the pc and the bas 100b. Line freq. This specifies the line frequency of the local a.C. Voltag...

  • Page 30: 3.10

    3-5 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...

  • Page 31: Method Menu

    4-1 4. Method menu 4.1 load/save method this allows an experimental method (.Mod) to be loaded or saved. Method files contain the parameters entered in for the method and control menus, and the results options. These operations are performed using standard windows file dialog boxes. 4.2 select mode ...

  • Page 32: 4.3

    4-2 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 a...

  • Page 33: 4.5

    4-3 4.5 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...

  • Page 34: 4.6

    4-4 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 require...

  • Page 35: 4.8

    4-5 4.8 hydrodynamic modulation this specifies additional parameters for the hydrodynamic modulation (hdm) technique (figure 4-7). Figure 4-7. Hydrodynamic modulation dialog box. Data processing this specifies the method for handling the a.C. Current output (lock-in or rectify). Rotate during quiet ...

  • Page 36

    4-6 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 ...

  • Page 37: 5. Control Menu

    5-1 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: 5.5 Run Options

    5-2 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). The data f...

  • Page 39: 5.6 List Run Data

    5-3 leaving just the data values. Note: car. Ret + linefeed format works differently than the other formats--it saves an exact copy of all lines listed on the screen during each run. C) the data from single experimental runs can be save automatically by clicking auto-save data for single runs. The p...

  • Page 40

    5-4 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 u ) is in series with the double-layer capacitance (c dl ) (figure 5-2). Since a faradaic impedance is no...

  • Page 41

    5-5 ru/ Ω measured rc time constant/ µ s measured ru/ Ω error of ru measurement/ % 50.3 38 29 -42 100.4 94 92 -8.4 150 146 145 -3.3 200 198 198 -1.0 250 250 249 -0.4 300 302 301 +0.3 347 350 349 +0.6 401 406 404 +0.7 452 360 449 -0.7 table 5-1. Measured resistance and time constant via exponential e...

  • Page 42

    5-6 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 fro...

  • Page 43: 5.8 Measure Rest Potential

    5-7 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 potent...

  • Page 44: 5.9 Measure Impedance

    5-8 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. The in...

  • Page 45: 5.11 Clean Electrode

    5-9 fi 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. Clean elec...

  • Page 46: 5.13 Cell On/off

    5-10 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 instrume...

  • Page 47: Math Menu

    6-1 6. Math menu 6.1 operators a variety of mathematical operations can be performed on either the x or y data. These are addition, subtraction, multiplication, division, reciprocal, square, square root, exponent and logarithm (figure 6-1). In addition, the slope of the baseline can be adjusted. Act...

  • Page 48

    6-2 exact cutoff frequency depends on both the electrochemical and smoothing techniques). There are 3 methods for digital smoothing. These are: a) a modified variable point linear smoothing routine (moving average) b) a variable point least squares smoothing routine (least square) c) a fourier convo...

  • Page 49: 6.3

    6-3 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, the experimental data is automatically smoothed at the...

  • Page 50: 6.4

    6-4 figure 6-3. Derivative dialog box. Differentiation of i is often used for accurate calculation of peak potentials (1st derivative) and half-wave potentials (2nd derivative). 6.4 convolution in addition to differentiation and integration, semi-differentiation and semi- integration are also common...

  • Page 51: 6.5

    6-5 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 ...

  • Page 52: Analysis

    7-1 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 usin...

  • Page 53

    7-2 experimental results - slope and intercept (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 ca...

  • Page 54

    7-3 peak current peak current peak potential peak potential baseline baseline peakarea peakarea ap 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...

  • Page 55

    7-4 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 p window are examined for continuity of sign; that is, there are three consecut...

  • Page 56

    7-5 a) symmetric curves - the baseline is the line between the two current minima in the range of e p + 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 p (figure...

  • Page 57

    7-6 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 (...

  • Page 58: 7.2

    7-7 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 not appropriate: for example, when using microelectrodes at low scan rates, as this produces a sigmoidal plot for cv. Half peak...

  • Page 59

    7-8 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 ...

  • Page 60: 7.3

    7-9 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- 8). Figure 7-8. Analysis calibration...

  • Page 61: 7.4

    7-10 click run to start the analysis. At the end of each sample run, the software will request the next sample. When all the samples have been run, the calibration curve for a specified peak can be examined by clicking plot. A report that lists the unknown concentration is saved as a .Rep file; the ...

  • Page 62

    7-11 unknown concentration is saved as a .Rep file; the results are also listed in the main window. Figure 7-10. Standard addition dialog box. Process is used for reprocessing of existing files (e.G., if incorrect standard additions or peak potentials were used initially). Since 3-digit run numbers ...

  • Page 63: Graphics Menu

    8-1 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 draggi...

  • Page 64: 8.2

    8-2 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). Figure 8-2. Graph...

  • Page 65

    8-3 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 c...

  • Page 66: 8.3

    8-4 multi-graph style the overlap option draws all curves on the same set of axes and the range of the axes is determined by the data in main memory. The tile option displays each data file on its own set of axes. 8.3 graph colors the colors of each feature on the graph can be selected (for both the...

  • Page 67: Print Menu

    9-1 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 per...

  • Page 68: 9.3

    9-2 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: 10.

    10-1 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. Control potential voltammetry (i vs. E) c...

  • Page 70

    10-2 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 squar...

  • Page 71

    10-3 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...

  • Page 72: 10.1

    10-4 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. The potential wave form for lsv ...

  • Page 73

    10-5 separation of the peak potentials is 57/n mv (n = number of electrons transferred per molecule). +e -e high initial low e 3 scan segments 2 1 t figure 10-2. Potential wave form for cv. The peak current for a reversible process is given by the randles-sevcik equation: i x n ad c p = − 2 69 10 5 ...

  • Page 74

    10-6 therefore, for a reversible process, i p is proportional to the concentration, c, and the square root of the scan rate, υ 1/2 . As discussed above, there are many parameters that can affect the shape of the cv curve. Slow electron transfer kinetics can increase the separation of the peak potent...

  • Page 75

    10-7 bas capsules 132 adsorption of reduced glutathione on a mercury surface 141 determination of heterogeneous electron transfer rate constant 264 electrochemical conversion of [feir 5 (co) 16 ] - to [feir 5 (co) 15 ] 3- 265 identification of the products of oxidation of [cpfe(co) 2 ] 2 using infra...

  • Page 76

    10-8 14 transient electrochemical response of thermal ruthenium oxide thin films in aqueous electrolytes, e.W. Tsai, p. Abraham and k. Rajeshwar, 9 (1990) 130. 15 electrochemistry of c60 and c70 fullerenes, a.W. Bott, 10 (1991) 137. 16 cyclic voltammetry in organometallic chemistry, a.W. Bott, 10 (1...

  • Page 77

    10-9 mode = cv general parameters initial e (mv) = 0 -3276 to 3276 high e (mv) = 0 -3276 to 3276 low e (mv) = 0 -3276 to 3276 scan rate = 100 1 to 51200 ( µ v/s) 1 to 51200 (mv/s) 1 to 300 (v/s) initial direction = negative negative or positive number of segments = 2 0 to 65535 sensitivity = 1 µ a/v...

  • Page 78

    10-10 frequency divider scan rate (mv/s) frequency divider scan rate (mv/s) 4 51200 200 1024 5 40960 201 1019 6 34166 202 1014 7 29257 203 1009 8 25600 204 1004 9 22755 205 999 10 20480 206 994 11 18618 207 989 12 17066 208 984 13 15753 209 980 14 14628 210 975 15 13653 .. .. 16 12800 .. .. 17 12047...

  • Page 79

    10-11 b) the sample interval (potential resolution) is dependent on the scan rate. The best potential resolution for the scan rates (for mv/s) are shown below. Scan rate ( ν )/mv/s resolution/mv ν ≤ 15753 1 17066 ≤ ν ≤ 29257 2 34166 ≤ ν≤ 40960 3 ν = 51200 4 cv c) the maximum number of data points th...

  • Page 80

    10-12 mode = logi the general and specific parameters for logi are the same as for lsv, with two exceptions. A) scan rates are only allowed in µ v/s, since very slow scan rates are generally used for logi experiments. The range for scan rate is 1 to 51200. B) the default sensitivity is set to auto; ...

  • Page 81: 10.2

    10-13 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 ...

  • Page 82

    10-14 e pulse width final e init. E t pulse width quiet time figure 10-5. Potential wave form for cc. Often, the initial potential is a potential at which no faradaic reaction occurs, and the final potential is a potential at which the faradaic reaction occurs very rapidly; that is, the electroactiv...

  • Page 83

    10-15 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...

  • Page 84

    10-16 time window i/t typical deviations ideal t -1/2 figure 10-8. Plot of i/t -1/2 vs. T for ca showing "time window" for condition of planar diffusion. Although ca and cc are not used to measure absolute concentrations, they can be used to measure changes in concentrations due to homogeneous chemi...

  • Page 85

    10-17 q dl is the charge due to charging of the working electrode, and q ads is the charge due to electrolysis of the adsorbed species, and is directly proportional to the surface concentration of the adsorbate. Of the three components, only q diff is time dependent. Therefore, the intercept of the ...

  • Page 86

    10-18 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 µ a/v 100 ma/v to 100 na/v (10 pa/v with the low current module) specif...

  • Page 87

    10-19 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 µ c/v sensitivity range is automatically discharged and reset to zero when it nears the voltage sat...

  • Page 88

    10-20 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 sensitivity = 1 µ a/v 100 ma/v to 10 pa/v specific pa...

  • Page 89: 10.3

    10-21 10.3 pulse techniques (scp, npv/p, dpv/p) the basis of all pulse techniques is the difference in the rate of decay of background and faradaic currents following a potential step. The background current decays exponentially, whereas the faradaic current decays as a function of 1/(time) 1/2 ; th...

  • Page 90

    10-22 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...

  • Page 91

    10-23 the sensitivity and detection limit of scp are similar to those of dc polarography (5 µ a/mm and 10 -5 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 essen...

  • Page 92

    10-24 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 ...

  • Page 93

    10-25 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 diffusio...

  • Page 94

    10-26 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 ...

  • Page 95

    10-27 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 -3...

  • Page 96

    10-28 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..

  • Page 97: 10.4

    10-29 10.4 square wave techniques (oswv, bswv/p) square wave techniques are related to both pulse techniques and a.C. Voltammetric techniques. They are similar to dpv/p in that the current response is a symmetric peak and that there is effective discrimination against background charging currents. T...

  • Page 98

    10-30 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-cycle...

  • Page 99

    10-31 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). This is significantly faster than th...

  • Page 100

    10-32 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...

  • Page 101

    10-33 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..

  • Page 102: 10.5

    10-34 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...

  • Page 103

    10-35 figure 10-21. A.C. Current response for acv/p. The phase angle for an ideal reversible system is 45 o , whereas for quasi-reversible systems (slow electron transfer), it is less than 45 o . Since reversibility depends on the timescale of the experiment, increasing the a.C. Frequency often caus...

  • Page 104

    10-36 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 ...

  • Page 105

    10-37 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. Analysis menu the auto option for results graph displays ...

  • Page 106

    10-38 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- 2...

  • Page 107

    10-39 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 = 1 µ a/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) = ...

  • Page 108

    10-40 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..

  • Page 109: 10.6

    10-41 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....

  • Page 110

    10-42 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. Typical current response for oswsv...

  • Page 111

    10-43 (for which careful cleaning and polishing of the glassy carbon electrode surface is required between experiments). The above method is called anodic stripping voltammetry (asv) since the stripping current is anodic. This method can be used for metal ions that can be readily reduced to the meta...

  • Page 112

    10-44 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 deposi...

  • Page 113

    10-45 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 comments a) sample width is the time at the end of the pulse ...

  • Page 114

    10-46 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 = 1 µ a/v 100 ma/v to 10 pa/v deposit time (sec) = 15 1 to 6553...

  • Page 115

    10-47 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). Alternative base...

  • Page 116: 10.7

    10-48 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 ...

  • Page 117

    10-49 direction and time. Steady state voltammograms have a characteristic sigmoidal shape. The faster mass transport can also increase the sensitivity for quantitative analysis, and the rotating disk electrode is often used for the deposition step of stripping experiments. The limiting current (mas...

  • Page 118

    10-50 rpm t quiet time init e final t b. A. 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 ...

  • Page 119

    10-51 figure 10-30. The modulated rotation rate used for hdm. Current t ∆ i i ω o 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, oxi...

  • Page 120

    10-52 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 ( µ v/s) 1 to 51200 (mv/s) 1 to 300 (v/s) rotation rate (rpm) = 400 0 to 10000 sensitivity = 1 µ a/v 100 ma/v to 100 na/v (10 pa/v with the low current module) specific ...

  • Page 121

    10-53 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. Therefore, ro...

  • Page 122: 10.8

    10-54 10.8 time base techniques these are chronoamperometric techniques; that is, the current is measured as a function of time. Generally, such techniques are used for amperometric titrations, amperometric sensors, flow cells, etc. The variation between the three techniques available on the bas 100...

  • Page 123

    10-55 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 th...

  • Page 124

    10-56 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 detectio...

  • Page 125

    10-57 sensitivity = 1 µ a/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 experimen...

  • Page 126

    10-58 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. C) pulse period is the time for one potential cycle, an...

  • Page 127

    10-59 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. E) the maximum data length is 2000 cycles...

  • Page 128: 10.9

    10-60 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...

  • Page 129

    10-61 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 resid...

  • Page 130

    10-62 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. In these cases...

  • Page 131

    10-63 10.9.2 electrocapillary measurement (ecm) electrocapillary curve measurement (ecm) is used to characterize mercury metal- solution interfaces, examining macroscopic equilibrium properties such as surface tension as a function of potential. Such measurements are useful in studies of the structu...

  • Page 132

    10-64 e 6.4 mv 1msec (1khz) potential interval t 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 multi...

  • Page 133

    10-65 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 n must be less than the previous current value. Graphics menu single graph displays the electrocapillary curve. Analysis menu the auto option for results...

  • Page 134

    10-66 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...

  • Page 135

    10-67 10.9.4 a.C. Impedance (imp) (n.B. The imp technique requires connection of the bas 100b/w with the bas impedance module) in voltammetric techniques, the potential is varied over a specific range and the current response is monitored. In any one experiment, the timescale remains constant (e.G. ...

  • Page 136

    10-68 10 sec 0.1 to 1.0 hz 10 mv amp 200 mv fs figure 10-43. An example of the white noise wave form used for imp. The presentation of the experimental data is complicated by the phase difference between the applied potential and the current response. The results can be represented in terms of imped...

  • Page 137

    10-69 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

    10-70 intermediate systems, the nyquist plot is a semi-circle at high frequencies (kinetic control) and changes to a straight line at low frequencies (diffusion control); that is, the different controlling influences can be detected in one experiment. Although the nyquist plot is the most commonly u...

  • Page 139

    10-71 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 sensitivity = auto auto, 100 ma/v to 1 µ a/v specific parameters freq. Increment (decade) = 1 1 or 2 100-1000 hz = 64 1 to 400 10...

  • Page 140: 11.

    11-1 11. Service and troubleshooting 11.1 preventative maintenance routine maintenance for the bas 100b consists of making certain that the forced air cooling systems are cleaned and checked regularly. Forced air is employed for both the power supply and circuit board enclosure. The cooling air inle...

  • Page 141: 11.3

    11-2 11.3 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...

  • Page 142

    11-3 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 supply check power supply call bas customer se...

  • Page 143

    11-4 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.

  • Page 144: 11.4

    11-5 11.4 removal of circuit boards b a c 2 4 1 3 4 2 pc boards 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 o...