CH-9101 Herisau/Switzerland Internet www.metrohm.com E-Mail info@metrohm.ch 2.757.01X0 757 VA Computrace 8.757.8023 Software Manual 31.08.
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Table of contents Table of contents 1 Introduction ...................................................................................... 1 1.1 Purpose of program ............................................................................ 1 1.2 General information............................................................................. 2 Hardware requirements for the PC ................................................ 2 Demo version ....................................................................
Table of contents 2.5 Utility menu ......................................................................................... 17 Computrace control selection...................................................... 17 Dosimat control selection ............................................................ 17 Film deposition selection ............................................................. 17 Cleaning procedure selection ...................................................... 17 2.6 User menu ................
Table of contents 3.5 Graphical settings.............................................................................. 49 Curve window elements............................................................... 49 Page properties............................................................................ 50 Axis properties ............................................................................. 51 Curve properties...........................................................................
Table of contents 5 Determination mode ............................................................. 71 5.1 Determination mode overview ......................................................... 71 Determination mode features ...................................................... 71 Determination mode selection ..................................................... 71 Determination mode windows ..................................................... 71 5.2 Working method specifications........................
Table of contents 5.5 Results............................................................................................... 103 Results window overview ........................................................... 103 Header........................................................................................ 104 Determination data..................................................................... 104 Sample data...............................................................................
Table of contents 6 Manual control ........................................................................ 125 6.1 Computrace control......................................................................... 125 Computrace control selection.................................................... 125 Computrace control window ...................................................... 125 6.2 Dosimat control................................................................................
Table of contents 7.5 Determinations ................................................................................. 141 Load a determination ................................................................. 141 Save a determination ................................................................. 141 Automatically save determinations ............................................ 141 Perform a determination ............................................................
Table of contents 8.5 General rules for VA trace analysis .............................................. 164 Chemicals and equipment......................................................... 164 Electrolytes ................................................................................. 164 Standard solutions ..................................................................... 164 Samples .....................................................................................
1.1 Purpose of program 1 Introduction 1.1 Purpose of program «VA Computrace 2.0» is the name of the control software for the PC-controlled 757 VA Computrace System for voltammetric analysis. This system consists of the following parts: 1.757.0010 VA Computrace Stand with accessories 3.757.1300 Add-on Board for PC or 6.5326.000 VA Computrace Interface 6.2135.010 Connecting Cable 6.6032.100 VA Computrace Software 2.
1 Introduction 1.
1.3 Installation 1.3 Installation Installation of software and VA Computrace Interface 1. Switch on PC and start operating system (Windows™ 2000) without connection of the VA Computrace Interface via USB cable. 2. Insert installation CD into CD drive. 3. If the autorun option for the CD drive is disabled, select and Run. Browse for the Setup.exe file on the installation CD and click on . 4. Click on "757" and follow the instructions given in the setup program.
1 Introduction Installation of software and add-on board 1. Switch off PC and disconnect power cable from the power socket. 2. Disconnect all other cables to computer peripherals (keyboard, display, printer, etc.). 3. Disassemble PC and install 3.757.1300 Add-on Board in a free ISA slot (see instruction manual of the PC). 4. Reassemble PC. 5. Switch off 757 VA Computrace Stand. 6. Connect the built-in add-on board to the "PC Interface" socket of the 757 VA Computrace Stand with the 6.2135.010 cable. 7.
1.3 Installation Software upgrade with add-on board If you want to upgrade from the 757 VA Computrace 1.0 software to the 757 VA Computrace 2.0 software on a PC with add-on board installed, proceed as follows: 1. Switch off 757 VA Computrace Stand. 2. Switch on PC and start operating system (Windows™ 98 or Windows™ 2000). 3. Select / Settings / Control panel and double-click the Software icon. 4. Select 757 VA Computrace in the list and click on to remove the VA Computrace 1.0 program.
1 Introduction 11. Restart the PC. 12. Connect the built-in add-on board to the "PC Interface" socket of the 757 VA Computrace Stand with the 6.2135.010 cable and switch on 757 VA Computrace Stand. 13. Start the VA Computrace 2.0 software. Installation of Dosimats Up to five 665 or 765 Dosimats can be connected to the 757 VA Computrace Stand. For the connection of 1 or 2 Dosimats, the 6.2141.080 Cable is used. Other cables for the connection of more than 2 Dosimats are available from Metrohm on request (e.
1.3 Installation 5. Make hardware settings for the 813 Compact Autosampler (see Automation, section 2.7). 6. Make hardware settings for Dosimats (see Hardware settings for Dosimats). 7. Define the addition or predose solution in the DOSIMATS window (see Dosimats, section 5.2). Hardware settings for Dosimats 1. Switch on PC and start operating system 95. 2. Start the VA Computrace software by double-clicking the program icon or starting the ct757.exe file. 3. Login without entering Name and Password.
1 Introduction 6. Close the VA Computrace software by clicking on lecting File / Exit. or se- 7. Switch on the Dosimats connected to the 757 VA Computrace Stand. 8. Switch on 757 VA Computrace stand. 9. Restart the VA Computrace software. Note: If Dosimats are connected to the 757 VA Computrace Stand, the instruments must always be switched on in the sequence Dosimat → 757 → PC. Deinstallation 1. Select / Settings / Control panel. 2. Double-click the Software icon. 3.
1.4 Overview of program windows 1.4 Overview of program windows VA Computrace 2.0 consists of different windows whose functionality is linked together.
1 Introduction 1.5 Overview of file types The following file types are produced by the 757 VA Computrace software: 1.6 *.dth Determination file (binary file) Contains determination data and method. The *.dth file is stored automatically in the Data folder if the autosave option is enabled in the GENERAL SETTINGS window. *.mth Method file (binary file) Contains the method. *.sig Signal file (binary file) Contains exploratory data and exploratory method. The *.
2.1 Main window overview 2 Main window 2.1 Main window overview Main window elements The MAIN WINDOW is the center of the VA Computrace software. Its elements are the menu bar, the tool bar and the status bar indicating user, method and determination.
2 Main window Main window icons It depends on the selected mode (exploratory or determination) whether the following icons are displayed in the MAIN WINDOW or not. Exit the VA Computrace 2.0 program. Print reports and curves. Switch to exploratory mode. Switch to determination mode. Load default parameters for exploratory or determination mode. Load existing method or signal file. Save method or signal file. Load existing determination file. Save determination file.
2.2 Starting/closing the program 2.2 Starting/closing the program Starting the VA Computrace program Start the Program Double-click the 757 VA Computrace icon or the Ct757.exe file to start the VA Computrace 2.0 program. The VA COMPUTRACE LOGIN window appears. Enter Name and Password and select the desired option Start measurements for starting measurements or Recalculate only for recalculation. Note: After software installation, the program can be started without entering Name and Password.
2 Main window 2.3 File menu Method files Method files (*.mth) contain all the specifications and parameters for running a determination. They can only be loaded or saved in the determination mode. MAIN WINDOW / File / New method (Ctrl+N) Load a standard template with DP mode for creating a new method. MAIN WINDOW / File / Load method (Ctrl+O) Load an existing method file. Normally, method files are stored in the Method folder.
2.3 File menu MAIN WINDOW / File / Save determination as ... Save the current determination loaded in the working memory in a new file. Enter name and directory for storage of the determination file. MAIN WINDOW / File / Export determination points Save the measurement points of all sweeps of the current determination loaded in the working memory into a data file (extension *.txt).
2 Main window Printing of reports and curves MAIN WINDOW / File / Print (Ctrl+P) Print reports and/or curves. Depending on the mode selection, a window appears for selection of the items to be printed (see section 4.4 for exploratory mode and section 5.7 for determination mode). MAIN WINDOW / File / Printer setup Selection of a printer and definition of paper size and format. Program exit MAIN WINDOW / File / Exit Quit the VA Computrace 2.0 program.
2.5 Utility menu 2.5 Utility menu Computrace control selection MAIN WINDOW / Utility / Computrace control Start manual control of 757 VA Computrace Stand (details see section 6.1). Dosimat control selection MAIN WINDOW / Utility / Dosimat control Start manual control of 665 or 765 Dosimats connected to the 757 VA Computrace Stand (details see section 6.2).
2 Main window User rights The «VA Computrace» program has a security system based on a list of user rights. For every user or user category, a password and different access levels can be defined. We recommend to make a new user list and enter passwords as a first action after system installation. MAIN WINDOW / User / User rights The USER RIGHTS window appears. User List of all users. The user rights are displayed for the selected and highlighted user.
2.6 User menu Password Change password for user. A " * " is displayed for each character entered. User rights The different user rights options can be changed for the selected user: none No access to this program part. R Permission to read in this program part. R/W Permission to read/write in this program part. Change allowance Permission to edit the user rights. Add a new user to the users list. The ADD NEW USER window appears. Name [ 13 characters; ] User name.
2 Main window Use default locations Set default directories for Data folder and Method folder. Data folder User specific folder for determination and signal files. Use to change the folder. Method folder User specific folder for method files. Use to change the folder. User rights overview MAIN WINDOW / User / Overview The OVERVIEW window displaying the list of all users appears. Detailed user list with all user rights. User list without user rights. User list with small icons.
2.7 Settings menu 2.7 Settings menu General settings MAIN WINDOW / Settings / General Settings In the GENERAL SETTINGS window default set- tings for autosaving and storage directories can be defined with the General tab. Auto save options Auto save determination and signal If this option is enabled, every signal or determination file is stored automatically in the data folder after the end of the measurement. Folders Selection of default directories.
2 Main window Hardware settings MAIN WINDOW / Settings / General Settings In the GENERAL SETTINGS window default set- tings for the add-on board, the VA Computrace Interface and the Dosimats can be defined with the Hardware tab. Interface Selection of the interface used to operate the 757 VA Computrace: ISA Card (IF020) 3.757.1300 Add-on board VA Computrace Interface 6.2155.000 VA Computrace Interface IF020 address IP address of the add-on board. I/O Mode Input/Output transfer mode for add-on board.
2.7 Settings menu Dosimat no. [ on, off; off ] Check this checkbox for each Dosimat connected. Volume (mL) [ 1, 5, 10, 20, 50 mL; 5 mL ] Volume of the exchange unit of the Dosimat Dose rate (mL/min) [ 0.001 ... 150 mL/min (depending on exchange unit) ] Dosing rate of the Dosimat. Note: If Dosimats are connected to the 757 VA Computrace Stand, the instruments must always be switched on in the sequence Dosimat → 757 → PC.
2 Main window Note: Method 2 must be set on the 813 Compact Autosampler. Time to move to sample (s) [ 30 s ; 25 ... 2147483647 s ] Maximum time needed for the 813 Compact Autosampler to move from one sample to the other. (minimum time allowed: 25 s). Sample transfer time (s) [ 300 s ; 30 ... 2147483647 s ] Time to transfer the sample solution from the sample vessel to the measurement vessel using the peristaltic pump of the 813 Compact Autosampler (minimum time allowed: 30 s). No.
2.8 Window menu 2.8 Window menu Tiling of windows MAIN WINDOW / Window / Tile All opened windows are tiled. Opening and closing of program windows MAIN WINDOW / Window / Working method specification (F6) The WORKING METHOD SPECIFICATIONS window will be opened or (if it is already open) closed (see section 5.2). MAIN WINDOW / Window / Monitor (F7) The MONITOR window will be opened or (if it is al- ready open) closed (see section 5.3).
2 Main window Display settings for Main window MAIN WINDOW / Window / Status bar Switch on/off display of status bar in the MAIN WINDOW. MAIN WINDOW / Window / Toolbar Switch on/off display of toolbar in the MAIN WINDOW.
3.1 Electrodes 3 General settings for exploratory and determination mode 3.1 Electrodes MME MME stands for Multi-Mode Electrode and is the working electrode commonly used in the 757 VA Computrace Stand. It combines the most important polarographic and voltammetric mercury electrodes in a single construction: DME Dropping mercury electrode SMDE Static mercury drop electrode HMDE Hanging mercury drop electrode For installation and maintenance of the Multi-Mode Electrode, see Hardware Manual.
3 General settings for exploratory and determination mode Hg drop surface t Voltage step time Notes: • In the exploratory mode, the DME can be used for all measurement modes except SqW, CV and PSA. In the determination mode, the DME can be used for all measurement modes except DC, SqW, CV and PSA. • An advantage of the DME compared with the SMDE is that the MME capillary is subjected to less mechanical stress.
3.1 Electrodes Notes: • In the exploratory mode, the SMDE can be used for all measurement modes except SqW, CV and PSA. In the determination mode, the SMDE can be used for all measurement modes except DC, SqW, CV and PSA. • An advantage of the SMDE compared with the DME is its greater sensitivity as the electrode surface and hence the baseline remains constant during the measurement. Further, less mercury is needed.
3 General settings for exploratory and determination mode RDE/SSE RDE stands for Rotating Disk Electrode and is used for direct and stripping determinations with Solid State Electrodes (SSE). Stirrer/RDE (rpm) [ 0...3000 rpm ; 2000 rpm ] Revolutions per minute of the rotating disk electrode. The stirring of the RDE remains active during all preparation procedure steps until the start of sweep. Surface t Notes: • The RDE can be used for all measurement modes.
3.2 VA measurement modes 3.2 VA measurement modes DP – Differential Pulse General: DP or Differential Pulse voltammetry is the most universal and frequently used voltammetric measurement mode. It is equally well suited for irreversible and reversible systems and offers a high sensitivity. The DP measurement mode can be set for the exploratory and determination mode by selecting DP - Differential pulse for the Mode parameter in the EXPLORATORY SPECIFICATION or WORKING METHOD SPECIFICATIONS window.
3 General settings for exploratory and determination mode Sweep parameters: Hydrodynamic (measurement) [ on, off ; off ] Enable/disable stirring of the RDE/SSE during the sweep. Start potential (V) [ -5...+5 V ; -0.9 V ] Start voltage for the voltage sweep. End potential (V) [ -5...+5 V ; -0.1 V ] Final voltage for the voltage sweep. Pulse amplitude (V) [ -1...+1 V ; 0.05 V ] Pulse amplitude of the voltage pulse superimposed on the direct voltage (pos. values = same direction; neg.
3.2 VA measurement modes SqW – Square Wave General: SqW or Square Wave voltammetry is primarly suitable for reversible electrode processes. It is used particularly for sensitive stripping voltammetric determinations at the HMDE or RDE. The SqW measurement mode can be set for the exploratory and determination mode by selecting SqW - Square wave for the Mode parameter in the EXPLORATORY SPECIFICATION or WORKING METHOD SPECIFICATIONS window.
3 General settings for exploratory and determination mode Sweep parameters: Hydrodynamic (measurement) [ on, off ; off ] Enable/disable stirring of the RDE/SSE during the sweep. Start potential (V) [ -5...+5 V ; -0.9 V ] Start voltage for the voltage sweep. End potential (V) [ -5...+5 V ; -0.1 V ] Final voltage for the voltage sweep. Voltage step (V) [ > 0 V ; 0.006 V ] Voltage step for direct voltage ramp. Amplitude (V) [ > 0...+1 V ; 0.
3.2 VA measurement modes DC – Sampled Direct Current General: DC or Sampled Direct Current voltammetry is the classic, simplest voltammetric measurement mode with limited sensitivity. It is mainly used for the investigation of reversible redox systems. The DC measurement mode can be set for the exploratory and determination mode by selecting DC - Sampled direct current for the Mode parameter in the EXPLORATORY SPECIFICATION or WORKING METHOD SPECIFICATIONS window.
3 General settings for exploratory and determination mode Sweep parameters: Hydrodynamic (measurement) [ on, off ; off ] Enable/disable stirring of the RDE/SSE during the sweep. Start potential (V) [ -5...+5 V ; -0.9 V ] Start voltage for the voltage sweep. End potential (V) [ -5...+5 V ; -0.1 V ] Final voltage for the voltage sweep. Voltage step (V) [ > 0 V ; 0.006 V ] Voltage step for direct voltage ramp. Voltage step time (s) [ > 0 s ; 0.
3.2 VA measurement modes NP – Normal Pulse (for "Exploratory" only) General: NP or Normal Pulse voltammetry is the classic pulse voltammetric measurement mode with direct recording of the current. It is equally well suited for irreversible and reversible systems and offers a higher sensitivity than the DC voltammetry. The NP measurement mode can only be set for the exploratory mode by selecting NP - Normal pulse for the Mode parameter in the EXPLORATORY SPECIFICATION window.
3 General settings for exploratory and determination mode Sweep parameters: Hydrodynamic (measurement) [ on, off ; off ] Enable/disable stirring of the RDE/SSE during the sweep. Start potential (V) [ -5...+5 V ; -0.9 V ] Start voltage for the voltage sweep. End potential (V) [ -5...+5 V ; -0.1 V ] Final voltage for the voltage sweep. Base potential (V) [ -5...+5 V ; -0.1 V ] Base voltage for voltage sweep. Pulse time (s) [ > 500 µs ; 0.
3.2 VA measurement modes CV – Cyclic Voltammetry General: CV or Cyclic voltammetry is mainly used to investigate the reversibility of electrode processes and for kinetic studies. The CV measurement mode can be set for the exploratory and determination mode by selecting CV - Cyclic voltammetry for the Mode parameter in the EXPLORATORY SPECIFICATION or WORKING METHOD SPECIFICATIONS window.
3 General settings for exploratory and determination mode Sweep parameters: Hydrodynamic (measurement) [ on, off ; off ] Enable/disable stirring of the RDE/SSE during the sweep. Start potential (V) [ -5...+5 V ; -0.9 V ] Start voltage for the voltage sweep. End potential (V) [ -5...+5 V ; -0.1 V ] Final voltage for the voltage sweep. Voltage step (V) [ > 0 V ; 0.006 V ] Voltage step for direct voltage ramp. Sweep rate (V/s) [ > 0 V/s ; 0.1 V/s ] Ramp slope = Voltage step / Voltage step time. No.
3.2 VA measurement modes PSA – Potentiometric Stripping Analysis General: PSA or Potentiometric stripping analysis with chemical oxidation is mainly used to determine substances in an organic matrix with the aid of mercury film electrodes without prior digestion. The PSA measurement mode can be set for the exploratory and determination mode by selecting PSA - Potentiometric stripping analysis for the Mode parameter in the EXPLORATORY SPECIFICATION or WORKING METHOD SPECIFICATIONS window.
3 General settings for exploratory and determination mode Sweep parameters: Hydrodynamic (measurement) [ on, off ; off ] Enable/disable stirring of the RDE/SSE during the sweep. Potential limit (V) [ -5...+5 V ; -0.1 V ] Voltage limit for PSA sweep. Maximum time (s) [ > 0 ; 20 s ] Time limit for PSA sweep. Notes: • The PSA measurement mode should only be used with RDE electrodes (mainly with Hg film).
3.2 VA measurement modes AC – Alternating Current Voltammetry General: AC or Alternating Current voltammetry is primarly suitable for reversible electrode reactions. It is virtually completely insensitive to irreversible reactions. The AC measurement mode can be set for the exploratory and determination mode by selecting AC - Alternating current voltammetry for the Mode parameter in the EXPLORATORY SPECIFICATION or WORKING METHOD SPECIFICATIONS window.
3 General settings for exploratory and determination mode Sweep parameters: Hydrodynamic (measurement) [ on, off ; off ] Enable/disable stirring of the RDE/SSE during the sweep. Start potential (V) [ -5...+5 V ; -0.9 V ] Start voltage for the voltage sweep. End potential (V) [ -5...+5 V ; -0.1 V ] Final voltage for the voltage sweep. Voltage step (V) [ > 0 V ; 0.006 V ] Voltage step for direct voltage ramp. Amplitude (V) [ -1...+1 V ; 0.
3.3 Potentiostat Notes: • The AC measurement mode can be used with all types of electrodes. • The following condition applies to the definition of the Modulation time: Modulation time > 2 / Frequency Modulation time < voltage step time + 0.45 s • The measurement time t (i) is defined as follows: t (i) = Modulation time / 2 3.3 Potentiostat The potentiostat built-in in the 757 VA Computrace Stand normally works with full sensitivity for current measurements from 100 pA to 30 mA.
3 General settings for exploratory and determination mode 2. Purging Optional purging of the sample solution during the Initial purge time (details see Purging). 3. Drop formation Hg drop formation at the MME if DME, SMDE or HMDE is selected (details see Electrodes, section 3.1). 4. Conditioning cycles Optional conditioning of solid state electrodes by applying cyclic conditioning sweeps (details see Conditioning). 5.
3.4 General operation sequence Purging Purging means saturation of the analysis solution with an inert gas and is used to remove the electrochemically active and hence interfering oxygen. With the inert gas flow rate of ca. 20 l/h set on the 757 VA Computrace Stand, a purging time of ca. 3...5 min usually suffices. For an effective purging of the analysis solution, the solution should also be stirred. Initial purge time (s) [ 0...
3 General settings for exploratory and determination mode • During the equilibration time, the start potential of the sweep is applied to the electrode. Cleaning potential (V) [ -5...+5 V ; -0.1 V ] Voltage applied to the electrodes during the Cleaning time. Cleaning time (s) [ 0...80600 s ; 0 s ] Time during which the Cleaning potential is applied to the electrodes. Deposition potential (V) [ -5...+5 V ; -0.9 V ] Voltage applied to the electrodes during the Deposition time. Deposition time (s) [ 0...
3.5 Graphical settings 3.5 Graphical settings Curve window elements All curve windows in the EXPLORATORY CURVES window, the DETERMINATION CURVES window and in the MONITOR window have the same elements which can be changed as desired in the GRAPHICAL PROPERTIES and the LINE PROPERTIES window (see below).
3 General settings for exploratory and determination mode Page properties The page properties of all curve windows can be set with the page tab of the GRAPHICAL PROPERTIES window. Borders Top [ ≥ 0 pt ; 45 pt ] Left [ ≥ 0 pt ; 65 pt ] Right [ ≥ 0 pt ; 30 pt ] Bottom [ ≥ 0 pt ; 45 pt ] Border size in points (distance between the curve window frame and the graphical window frame inside the curve window). Colors Color of border in the curve window. Color of curve background in the curve window.
3.5 Graphical settings Axis properties The axis properties for the x and y axis of all curve windows can be set with the x axis or y axis tab of the GRAPHICAL PROPERTIES window. Range (for x axis) From [ -5...+5 V ; -1 V ] Lower limit for x axis (voltage). To [ -5...+5 V ; -1 V ] Upper limit for x axis (voltage). Range (for y axis) From [ > 0 ; -1e-10 ] Lower limit for y axis (current for VA techniques, dt/dE for PSA).
3 General settings for exploratory and determination mode Format Format for labels of the x or y axis. Check one of the following options: Decimal ± ##.### (floating point number) Scientific ± #.### e ± ### Engineering ± ###.## + prefix Precision [ ≥ 0 ; 3 ] Total number of significant digits for labels of the x or y axis. Ticks Definition of major and minor ticks for x or y axis. No. [ ≥ 0 ; 8 ] Number of major or minor ticks for x or y axis.
3.5 Graphical settings Curve properties The drawing properties for all curves can be set with the appropriate ..... curve tab of the GRAPHICAL PROPERTIES window. Type Line Connect the measurement points by a straight line. Scattered Draw a symbol for each measurement point. Both Connect the measurement points by a straight line and draw a symbol for each point. Line style Selection of line style of the curve in the LINE PROPERTIES window (see Line properties).
3 General settings for exploratory and determination mode Line properties Definition of line properties for axes or curve lines. Style [ different styles ; Solid ] Style of the line. Width [ 0...8 ; 0 ] Width of the line in points (0 = hair line). Color of the line.
4.1 Exploratory mode overview 4 Exploratory mode 4.1 Exploratory mode overview Exploratory mode features The program part "Exploratory" has been especially designed for practice-oriented qualitative voltammetric analysis. It comprises seven different measurement techniques and is curve oriented. You are shown voltammograms and the associated parameters in two windows next to each other. The various voltammograms can be superimposed on one another thus making comparison of the curves extremely simple.
4 Exploratory mode 4.2 Exploratory specification window Exploratory specification settings The EXPLORATORY SPECIFICATION window contains all settings for performing measurements in the exploratory mode. Most of the settings are identical for exploratory and determination mode and are therefore described in section 3. Electrode see Electrodes, section 3.1 Drop size see Electrodes, section 3.1 Stirrer see Stirring, section 3.4 see Potentiostat, section 3.
4.2 Exploratory specification window Signal Selection of a signal file to be shown with the Selected signal properties. An asterisk * marks the signal file whose parameters are loaded. Mode Selection of VA measurement mode, see VA measurement modes, section 3.2 Sweep Parameters of the selected VA measurement mode, see VA measurement modes, section 3.2 Stand-by potential see Stand-by potential, section 3.4 Load/save signals Signal files (*.
4 Exploratory mode EXPLORATORY SPECIFICATION / File / Export voltammetric parameters ... Save the voltammetric parameters of the current signal loaded in the working memory into an ACSII file (extension *.txt). The files can be imported into spreadsheet programs like Microsoft Excel or into text programs like Microsoft Word. Transfer parameters and data Measurement parameters and/or data points of signal files can be transferred between the exploratory mode and the determination mode.
4.2 Exploratory specification window Performing exploratory measurements Measurements in the exploratory mode can be performed using the following icons (in the MAIN WINDOW) or buttons (in the EXPLORATORY SPECIFICATION window): Start measurement The operation sequence (see section 3.4) defined in the EXPLORATORY SPECIFICATION window is started. Each step of the operation sequence is listed in the first line of the status window beside the button.
4 Exploratory mode 4.3 Exploratory curves Exploratory curves window The EXPLORATORY CURVES window shows all curves of the signals loaded and (if a voltage sweep is running) the live curve. If a signal file is loaded or measured, the axes have the following orientation: x axis The previously loaded or measured signal is displayed from the left to the right. For cyclic sweeps, the forward sweep is displayed from the left to the right.
4.3 Exploratory curves Select signal curves One of the signal curves loaded into the EXPLORATORY CURVES window is always shown with Selected signal properties which can be set different from all other curves loaded (see Curve properties, section 3.5). The selection of this signal file is done in the Signal field of the EXPLORATORY SPECIFICATION window. An asterisk * in this field marks the signal file whose parameters are loaded in the EXPLORATORY SPECIFICATION window. Only this signal file can be stored.
4 Exploratory mode EXPLORATORY CURVES / Plot / Dynamic signal properties The properties of the dynamic signal curve (live curve) can be set with the Dynamic curve tab of the GRAPHICAL PROPERTIES window (details see Curve properties, section 3.5). EXPLORATORY CURVES / Plot / Selected signal properties The properties of the selected signal curve can be set with the Selected curve tab of the GRAPHICAL PROPERTIES window (details see Curve properties, section 3.5).
4.3 Exploratory curves Signal cursor EXPLORATORY SPECIFICATION / Signal / Signal cursor Open the SIGNAL CURSOR window for selection of measurement points. The X and Y value of the selected point is displayed in the window. Move cursor to the next or to the preceding measurement point on the selected signal. Peak search Automatic or manual peak evaluation of recorded signal curves.
4 Exploratory mode General parameters for peak evaluation. Options Manual Manual peak evaluation. The base points for baseline evaluation must be set manually. Automatic Automatic peak evaluation. The base points for baseline evaluation are evaluated automatically. Reverse peak Enable peak evaluation of reverse peaks (peaks with opposite direction compared to the sweep direction: negative peaks with anodic sweeps; positive peaks with cathodic sweeps).
4.3 Exploratory curves or by pressing the ↑ or ↓ key. If the automatic peak evaluation is selected, n/a is displayed and the field can not be edited. End (V) [ Start potential...End potential ; - ] Manual setting of the end base point for baseline evaluation. The values can be increased or decreased by clicking the buttons of the field or by pressing the ↑ or ↓ key. If the automatic peak evaluation is selected, n/a is displayed and the field can not be edited.
4 Exploratory mode Table of results Display of peak evaluation results. No. Number of evaluation result. This number is also displayed in the EXPLORATORY CURVES window. Clicking this number with the right mouse button offers the following menu: Edit baseline Open the EDIT BASELINE window for further modifying the peak evaluation for the selected peak (see Edit peak). Copy Copy the selected results line of the table to the clipboard.
4.3 Exploratory curves Edit peak Modify the peak evaluation of an already found peak. The results are displayed in the PEAK SEARCH window. This window is opened by clicking the number of a found peak in the PEAK SEARCH window with the right mouse button and selecting the menu point Edit peak. Begin Manual setting of the start base point for baseline calculation.
4 Exploratory mode Wave evaluation Automatic wave evaluation of recorded DC or NP signal curves. The results (position of half-wave potentials and wave height) are listed in the table of results, the calculated tangents and positions of the half-wave potential are displayed in the EXPLORATORY CURVES window. EXPLORATORY SPECIFICATION / Signal / Wave evaluation Open the PEAK SEARCH window for starting the quantitative wave evaluation. General parameters for wave evaluation.
4.3 Exploratory curves Start wave evaluation with the current parameters entered in the WAVE EVALUATION window. The calculated positions of the half-wave potentials and tangents are displayed in the EXPLORATORY CURVES window. Table of results Display of wave evaluation results. No. Number of evaluation result. This number is also displayed in the EXPLORATORY CURVES window.
4 Exploratory mode 4.4 Printing in exploratory mode MAIN WINDOW / File / Print (Ctrl+P) Print exploratory specifications and/or curves. The PRINT EXPLORATORY window appears for selection of the items to be printed. With Print curves enabled, the content of the EXPLORATORY CURVES window is printed on the upper half of the page if the portrait format is selected for the printer or on the whole page, if landscape format is selected. Curves and voltammetric parameters are always printed on separate pages.
5.1 Determination mode overview 5 Determination mode 5.1 Determination mode overview Determination mode features The program part "Determination" is used for quantitative voltammetric analysis of inorganic and organic substances. It comprises six different measurement modes and the possibility for stripping techniques. Quantitative evaluation can be performed via standard addition or calibration curve.
5 Determination mode MAIN WINDOW / Window / Monitor (F7) The MONITOR window will be opened or (if it is al- ready open) closed. It serves to start a determination using the working method and shows the live display of the running determination curves. MAIN WINDOW / Window / Determination curves (F8) The DETERMINATION CURVES window will be opened or (if it is already open) closed.
5.2 Working method specifications MAIN WINDOW / File / Save method as ... Save the current method loaded in the working memory as a new file. Enter name and directory for storage of the method file. 757 VA COMPUTRACE / File / Export results ... Save the full report of the current determination loaded in the working memory as an ASCII file (*.txt). This file can be imported into spreadsheet programs like Microsoft Excel or into text programs like Microsoft Word.
5 Determination mode Remark2 [ 0...68 characters ; ] Remark 2 regarding the method. Calibration [ see below ; Standard addition manual ] Selection of calibration mode (see also section 5.7): Standard addition Standard addition. The number of additions is defined in the Determination tab, the standard addition solutions are defined in the Substances tab, and the Dosimats are defined in the DOSIMATS window. Sample with calibration curve Sample determination using previously recorded calibration curves.
5.2 Working method specifications Drop size Drop size for SMDE or HMDE (see Electrodes, section 3.1). Stirrer Stirrer settings (see Stirring, section 3.4). Dosimat settings (see Dosimats). Potentiostat settings (see Potentiostat, section 3.3). Edit working method parameters (see Determination, Voltammetric, Substances, and Documentation). Determination The Determination tab of the EDIT WORKING METHOD PARAMETERS window contains general specifications for performing the determination.
5 Determination mode Cell volume (mL) [ > 0 mL ; 10 mL ] Total volume of solution (sample + auxiliary solution, e.g. buffer) in the measuring vessel at the start of the determination. The sample concentrations Mass conc. calculated refer to this cell volume. Measure blank [ on, off ; off ] Measure a blank solution before sample determination. The blank curve is then automatically subtracted from all subsequent measured curves.
5.2 Working method specifications No. of replications [ 0...10 ; 2 ] Number of replications (= total number of measurements) for each variation (sample, standard addition, calibration level). Voltammetric The Voltammetric tab of the EDIT WORKING METHOD PARAMETERS window contains parameters for preparation procedures and VA measurement modes. The parameters displayed depend on the measurement mode selected in the WORKING METHOD SPECIFICATIONS window.
5 Determination mode Substances The Substances tab of the EDIT WORKING METHOD PARAMETERS window contains parameters for the definition and recognition of substances, for the definition of standard solutions, for peak evaluation and results calculation. The parameters displayed depend on the calibration technique selected in the WORKING METHOD SPECIFICATIONS window. Substance [ 8 characters ; ] Substance name.
5.2 Working method specifications rameters are not displayed if Batch with solution exchange is selected for Technique. No. [ 1...5 ; 0 ] Number of addition solution to be used for manual or automatic addition. For automatic additions, this number is also the Dosimat number. If a mixed standard solution is used, the number of this solution must be entered for each substance present in the mixed solution. Conc. [ > 0 ; 0 ] Value for concentration of addition solution. Unit [ µg/L...
5 Determination mode Nonlinear Regression (through Zero) The regression is calculated with a nonlinear curve forced to the zero point. This option is only available if Record calibration curve is selected for Calibration. Peak evaluation [ Height, Area, Derivative ; Height ] Selection of peak evaluation quantity: Height Peak height from baseline to peak maximum. Area Peak area between peak curve and calculated baseline.
5.2 Working method specifications Baseline The BASELINE window contains the settings for baseline evaluation for a single "variation" measurement (= all replications of a sample, standard addition or calibration measurement) of a substance and is opened by clicking the button for the selected substance in the Bsln. column in the Substances tab of the EDIT WORKING METHOD PARAMETERS window. Auto. [ on, off ; on ] Enable/disable the automatic peak evaluation. Begin [ -5...
5 Determination mode Calculations The Calculations tab in the EDIT WORKING METHOD PARAMETERS window contains a table with all formulae used for the calculation of the final results for a substance. Substance Selection of the substance with its calculation formulae. Calculations Display of defined calculation formulae. Name Name of the calculation formula. Double-clicking the name opens the CALCULATION window for edition of the formula. Formula Display of calculation formula.
5.2 Working method specifications Calculation The CALCULATION window is opened if a new formula is added or an existing formula is edited on the Calculations tab of the EDIT WORKING METHOD PARAMETERS window. It contains the formula and parameters for the calculation of a final result for a substance. Formula General calculation formula for the final result. Name User-defined name for the calculation formula. Multiplier [ any number ; 1 ] Multiplier for calculation formula.
5 Determination mode Volume (mL) [ > 0.01 mL ; 0 mL ] Addition volume for each addition. Switch to the previous page of this window. Switch to the next page of this window. Concentrations of calibration solutions If Batch with solution exchange is selected for Technique, the concentrations of the calibration solutions must be entered in the CELL CONCENTRATIONS window which is opened by clicking the button for the selected substance in the Substances tab of the EDIT WORKING METHOD PARAMETERS window.
5.2 Working method specifications Documentation In the Documentation tab of the EDIT WORKING METHOD PARAMETERS window the elements for the automatic documentation printout at the end of the determination are defined. These settings belong to the method and are stored with it. Results Automatic printout of Full report or Short report. Font size Font size in points for report printout. Comment Automatic printout of the method comment defined in the accompanying field.
5 Determination mode Determination method Automatic printout of the method parameters used for the determination. Working method Automatic printout of the method parameters of the working method in the working memory. Order [ 1...6 ; ] Order of printout for the element. Save final results as ASCII file Automatic storage of the full report into an ASCII file. Path 86 Path for saving the selected report elements into an ASCII file. Use to change the path.
5.2 Working method specifications Dosimats The automatic use of 665 or 765 Dosimats for the addition of solutions has to be defined in the DOSIMATS window which is opened by clicking the button in WORKING METHOD SPECIFICATIONS window. Note: Make sure, that the desired Dosimat has also been checked on the Hardware tab of the GENERAL SETTINGS window (see section 2.7). Dosimat used [ on, off ; off ] Checkbox for Dosimats used for automatic addition of solutions.
5 Determination mode 5.3 Monitor Start determination If no determination is running, the MONITOR window is used to start a new determination with the current working method. Start determination The operation sequence (see section 3.4) defined in the working method is started. If the previous determination has not been saved, the SAVE CONFIRMATION window appears. Start the new determination without saving the previous determination. Save the previous determination before starting the new determination.
5.3 Monitor Stop/Hold determination A running determination can be stopped, interrupted and continued. Each step in the operation sequence can be abbreviated by clicking the button. Stop determination Stop running determination immediately. Hold determination Interrupt running determination. Continue determination Continue an interrupted determination. Next step Break off the running step and go to next step of the operation sequence.
5 Determination mode The progress indicator below this field shows the progress of the determination. The details of the running operation sequence step are displayed in the first line of the status field below the progress indicator. In the second line of the status field comments or error messages concerning the running determination are displayed. The red light at the right side of the status field indicates a current overload. In this case, stop the measurement and change the measurement parameters.
5.3 Monitor Sample ID [ 16 characters ; "std" ] Identification for sample. Sample size [ > 0 ; 10 ] Amount of sample added to the measuring vessel. The value defined on the Determination tab is displayed and can be changed if desired. Sample unit [ mL, g ; mL ] Selection of unit for sample amount. The value defined on the Determination tab is displayed and can be changed if desired. Cell volume (mL) [ > 0 mL ; 10 mL ] Total volume of solution (sample + auxiliary solution, e.g.
5 Determination mode MANUAL ADDITION This window appears at the start of each manual addition of standard solutions for standard addition determinations or the recording of calibration curves. Add (from solution no. X) (ml) [ > 0.01 ml ; 0 ml ] The addition volume for the manual addition defined in the Substances tab is displayed and can be changed if desired. Add the addition solution into the measuring vessel and press .
5.3 Monitor Graphical properties for monitoring curves The graphical properties for curves in the MONITORING window can be set by selecting the options of the context sensitive menu. MONITORING / Page properties The page properties of the MONITORING window can be set with the page tab of the GRAPHICAL PROPERTIES window (details see Page properties, section 3.5).
5 Determination mode 5.4 Determination curves Load/save determinations Determination files (*.dth) contain the measurement data and the determination method used. Existing files can be loaded, saved again and exported by the following commands: MAIN WINDOW / File / Load determination Load an existing determination file into the working memory. The name of the determination loaded is displayed in the status bar of the MAIN WINDOW.
5.4 Determination curves Determination curves window The DETERMINATION CURVES window shows the determination and calibration curves of the loaded determination. The DETERMINATION CURVES window contains the following ten subwindows which can be enlarged or reduced inside the DETERMINATION CURVES window by moving the frames with the mouse: List of curves The top subwindow lists all available curves of the determination with the evaluated peak heights.
5 Determination mode Edit determination method parameters DETERMINATION CURVES / Edit / Determination method parameters Open the EDIT DETERMINATION METHOD PARAMETERS window for viewing and modifying the parameters of the determination method used to record the determination. This window contains the tabs Specifications, Determination, Voltammetric, Substances and Calculations.
5.4 Determination curves Title [ 0...68 characters ; "Method title" ] Method title. Remark1 [ 0...68 characters ; ] Remark 1 regarding the method. Remark2 [ 0...68 characters ; ] Remark 2 regarding the method. Calibration [ read only ] Display of the calibration mode used for the determination (details see Working method specifications window, section 5.2).
5 Determination mode Substances The Substances tab of the EDIT DETERMINATION METHOD PARAMETERS window contains parameters for the definition and recognition of substances, for the definition of addition solutions, for peak evaluation and results calculation. For details, see the identical Substances tab of the EDIT WORKING METHOD WINDOW, section 5.2.
5.4 Determination curves Automatic Switch on/off the automatic peak baseline evaluation. Begin Manual setting of the start base point for baseline evaluation. The base point can be moved either by manually changing the voltage value in the first field or by clicking the buttons of the second field indicating the current value. This field can only be edited if Automatic is disabled. End Manual setting of the end base point for baseline evaluation.
5 Determination mode Auto scaling DETERMINATION CURVES / Plot / Auto scale (F4) Reset zooming and scale x and y axes so that all measurement points of all determination curves are visible. Swap axis DETERMINATION CURVES / Plot / Swap axis / abscissa Swap x axis for the current determination curve. DETERMINATION CURVES / Plot / Swap axis / ordinate Swap y axis for the current determination curve.
5.4 Determination curves DETERMINATION CURVES / Plot / Properties / Curves window The page properties of the determination curves subwindow can be set with the page tab of the GRAPHICAL PROPERTIES window (see Page properties, section 3.5). The properties of the x and y axis can be set with the x axis and y axis tab of the GRAPHICAL PROPERTIES window (see Axis properties, section 3.5).
5 Determination mode Graphical properties for calibration curves The graphical properties for calibration curves in the calibration curves subwindows can be set by selecting the options of the context sensitive menu. DETERMINATION CURVES / Page properties The page properties of the calibration curves subwindows can be set with the page tab of the GRAPHICAL PROPERTIES window (see Page properties, section 3.5).
5.5 Results 5.5 Results Results window overview The RESULTS window contains the current full report for the loaded determination. If the determination is recalculated, the RESULTS window is automatically renewed. ==================== METROHM 757 VA COMPUTRACE (5.757.0020) ==================== Determ. : 07171553_5ppm CdPb SMDE bl.
5 Determination mode The RESULTS window comprises the following parts: Header Metrohm 757 VA Computrace Name of manufacturer and instrument. (5.757.0020) Version number of PC software. Determination data Determ. Name of determination file. Sample ID Identification for sample (see Sample identifier on the Determination tab). Creator Name of the logged-in user who started the determination with Date and Time of determination start.
5.5 Results Method data Method File name of the method used for the determination. Title Method title. Remark1 Remark 1 regarding the method. Remark2 Remark 2 regarding the method. Substance evaluation Substance Substance name (see Substance on the Substances tab, section 5.2). Mass conc. Calculated substance mass concentration referring to the total volume of solution (Cell volume) in the measuring vessel at the start of the first sweep. MC.dev.
5 Determination mode Comments Display of comments if any type of error appeared in the sweep (e.g. Ovl. in scan = Overload during sweep; Ovl. in CDE = Overload during cleaning or deposition; Ovl. in cond. cycles = Overload during conditioning cycles; No peak found = no peak found for defined substance; Not used = peak is not used for calculation). Calibration data Substance Substance name (see Substance on the Substances tab, section 5.2). Calibr. Calibration technique std.add., rec.cc., or smp.cc.
5.5 Results Final results Final results Calculated results for the calculation formulae defined in the CALCULATION window. Res.dev. Absolute and relative deviation of the final results. Copy text to clipboard Text selected in the RESULTS window can be copied to the clipboard by selecting the Copy to clipboard option of the context sensitive menu. RESULTS / Select all Select the whole text in the RESULTS window. RESULTS / Copy to clipboard Copy the selected text to the clipboard.
5 Determination mode 5.6 Sample table The SAMPLE TABLE window shows the sample data of the loaded sample table. Pos. [ 1, 3, 5 ... 127; read only ] Position of the sample on the sample rack of the 813 Compact Autosampler. Only odd numbers are displayed, since for every sample a vessel containing rinsing solution must be placed at the even sample rack positions. Sample ID [ 16 characters ; "sample" ] Identification for sample. Amount [ > 0 ; 10 ] Amount of sample added to the measuring vessel.
5.6 Sample table Status [ read only ] Display of sample determination status: Measuring, Done or "empty" (ready for start). Add a new sample data row. The SAMPLE window for entry of Sample ID, Sample amount, Sample unit, and Cell volume is opened. Edit the selected sample data row. The SAMPLE window for modification of Sample ID, Sample amount, Sample unit, and Cell volume is opened. Reset the Status of the sample data rows to "empty" in order to restart the current sample table.
5 Determination mode Edit sample table The addition of new rows or the modification of existing rows in the sample table is done in the sample table window using the or button. In addition to this commands, the following possibilities for edition are available: SAMPLE TABLE / Edit / Cut Cut the selected sample data row and copy it to the clipboard. SAMPLE TABLE / Edit / Copy Copy the selected sample data row to the clipboard.
5.7 Printing in determination mode 5.7 Printing in determination mode MAIN WINDOW / File / Print (Ctrl+P) Print reports and/or curves. The PRINT OPTIONS window appears for selection of the elements to be printed. Results Printout of Full report or Short report. Font size Font size in points for report printout. Comment Printout of the method comment defined in the accompanying field. Determination curves Printout of all determination curves. Calibration Printout of all calibration curves.
5 Determination mode Determination method Printout of the method parameters used for the determination. Working method Printout of the method parameters of the working method in the working memory. Order [ 1...6 ; ] Order of printout for the element. Sample table Printout of the sample table.
5.8 Data processing and evaluation 5.8 Data processing and evaluation Data transfer After the start of a determination, the parameters of the current working method are copied into the determination method. The parameters necessary for the VA measurement are then sent from the PC to the Add-on board via TCP/IP connection or to the VA Computrace Interface via USB connection.
5 Determination mode In connection with the measured value recording, the following rules apply to the sweeps: • The maximum number of variations (V) is limited to 29, the maximum number of replications (R) to 10. • The maximum number of measured values is memory limited. If the memory needed for storage of the measured values extends 2 MB, the message There is not enough memory available to measure the desired points appears. In this case, reduce the number of data points per sweep.
5.8 Data processing and evaluation Peak recognition With the derived curves a search is made for successive minima and maxima. A maximum followed by a minimum indicates a normal peak, a minimum followed by a maximum a reverse peak. With the aid of these measured maxima and minima values, the Peak voltage and Peak width values are determined for each peak. After the peak detection a baseline is constructed.
5 Determination mode Baseline calculation Recognized peaks are evaluated using approximated baselines. The calculation of a baseline for a smoothed substance peak is determined by the baseline parameters set for this substance in the BASELINE window (see section 5.2).
5.8 Data processing and evaluation Evaluation quantity calculation The peak evaluation quantity is identical for all peaks of a determination and must be set on the Substances tab of the EDIT WORKING METHOD PARAMETERS window (see section 5.2). With the aid of the calculated baselines, the set evaluation quantity Height, Area or Derivative is determined for each substance peak and displayed as a result.
5 Determination mode Dilution calculation In all cases in which the sample volume is diluted in the measuring vessel (e.g. by addition of buffer) before the start of the first sweep, this must be taken into consideration by entering the two parameters Sample amount and Cell volume on the Determination tab of the EDIT WORKING METHOD PARAMETERS window (see section 5.2). If the sample is additionally diluted after the start of the first sweep (e.g.
5.8 Data processing and evaluation Std.dev.(n) Standard deviation of the individual value EV(n) = s(n) c(n) – c(s) Difference in the mass concentrations between the spiked sample n and the original sample solution 3. Determination of standard addition curve For the calculation of the linear standard addition curve, the parameters a and b of the linear regression curve y = a + bx are calculated by weighted least square minimization with y = EV and x = c – c(s).
5 Determination mode Rules for standard addition Standard addition is the usual calibration method for the majority of the applications possible with the 757 VA Computrace. Its advantage lies in its high dependability as the calibration in the sample takes place under real matrix conditions and all measurement parameters remain unchanged.
5.8 Data processing and evaluation Calibration curve calculation The content determination using a calibration curve is performed in two steps: • First the relation between the mass concentration c of a substance and the evaluation quantity EV is determined by measuring different reference solutions. • Finally, the sample is measured and its mass concentration c(s) determined using the recorded calibration curve.
5 Determination mode a = Y.reg/offset Intercept of calibration curve b = Slope Slope of calibration curve in the linear region d = Nonlin. Non-linearity factor Linear Calibration solutions EV Nonlinear Slope Linear (trough Zero) Nonlinear (trough Zero) Y.offset 0 0 c(eff) 3. Measurement of sample solution The sample solution with the unknown mass concentration c(s) of the sample is measured one or more times (defined by No. of replications).
5.8 Data processing and evaluation 5. Calculation of result deviation MC.dev. The total deviation of the calculated substance mass concentration Mass.conc. is determined using a linear error calculation which takes into account both the error contribution from the measurement and that from the calibration. Independent of the number of measurements, the total deviation MC.dev. is always calculated in a way that Mass.conc. ± MC.dev.
5 Determination mode • Determining the working range The calibration curve is defined only for the range between the calibration solutions with the lowest and highest mass concentrations. Extrapolations outside this range are not allowed. • Keep temperature constant Owing to the large temperature dependence of the measured values (≥ 2%/°C), it is advisable to work with the 6.1418.220 thermostatted measuring vessel.
6.1 Computrace control 6 Manual control 6.1 Computrace control Computrace control selection MAIN WINDOW / Utility / Computrace control Start manual control of the 757 VA Computrace Stand. Computrace control window The COMPUTRACE CONTROL window serves for manual control of the 757 VA Computrace Stand.
6 Manual control 10 mA ... 100 nA Selection of current range for measurement in the manual control mode. I ovl Indication of current overload by red light. Switch on/off current measurement. If switched on, the set Potential is applied to the electrodes and the current is measured continuously. This mode is indicated by the red light beside the | button. Potential (V) [ -5...+5 V ; 0 V ] Voltage to be applied to the electrodes. |
6.2 Dosimat control 6.2 Dosimat control Dosimat control selection MAIN WINDOW / Utility / Dosimat control Start manual control of the 665 or 765 Dosimats connected to the 757 VA Computrace Stand. Dosimat control window The DOSIMAT CONTROL window serves for manual control of the Dosimats connected to the 757 VA Computrace Stand. Burette Selection of the Dosimat to be controlled manually. Switch on dosing by Dosimat. The solution is dispensed until the button is pressed.
6 Manual control Dosed volume (mL) [ read only ] Display of current volume dispensed since last filling (first value) and accumulated volume if the display is not reset after filling (value in brackets). Reset Dosed volume display and fill burette cylinder. 6.3 Film deposition Film deposition selection MAIN WINDOW / Utility / Film deposition Start Hg deposition for solid state electrodes in the 757 VA Computrace Stand.
6.3 Film deposition Purge time (s) [ 0...80600 s ; 300 s ] Time of inert gas purging before the first measurement of the sample solution. Conditioning cycles Before deposition, the solid state electrode can be electrochemically regenerated by a freely selectable number of conditioning cycles. For every cycle, the voltage is changed at a sweep rate of 1 V/s to the End potential and then decreased at the same rate back to the Start potential. Start potential (V) [ -5...+5 V ; -1.
6 Manual control 6.4 Cleaning procedure Cleaning procedure selection MAIN WINDOW / Utility / Cleaning procedure Start cleaning procedure for solid state electrodes at the 757 VA Computrace Stand. Cleaning procedure window The CLEANING PROCEDURE window serves for electrochemical cleaning of solid state electrodes at the 757 VA Computrace Stand. Cleaning solution [ XXX characters ; ] Name of cleaning solution used for electrochemical cleaning of solid state electrodes. Stirrer/RDE (rpm) [ 0...
6.4 Cleaning procedure Start potential (V) [ -5...+5 V ; -1.2 V ] Start voltage for the cyclic conditioning sweep. End potential (V) [ -5...+5 V ; -0.1 V ] Final voltage for the cyclic conditioning sweep. No. of cycles [ 0...X ; 0 ] Number of conditioning cycles. Cleaning potential (V) [ -5...+5 V ; -0.1 V ] Voltage applied to the electrodes during the Cleaning time. Cleaning time (s) [ 0...80600 s ; 0 s ] Time during which the Cleaning potential is applied to the electrodes.
6 Manual control 132 757 VA Computrace – Software
7.1 Installation and program start 7 How to ...? 7.1 Installation and program start Install Dosimats for automatic addition 1. Connect 665 or 765 Dosimats to the 757 VA Computrace Stand (see Installation of Dosimats, section 1.3). 2. Make hardware settings for Dosimats (see Hardware settings for Dosimats, section 1.3). 3. Define the addition or predose solution in the DOSIMATS window (see Dosimats, section 5.2). Switch on the instruments and start program 1.
7 How to ...? 7.2 User rights Define a new user 1. Open the USER RIGHTS window by clicking on MAIN WINDOW / User / User rights. 2. Click the window. button to open the ADD NEW USER 3. Enter the Name and Password of the new user. 4. Close the ADD NEW USER window by clicking . 5. Select the new user in the list of all users and set his user rights (see User rights, section 2.6). 6. Close the USER RIGHTS window by clicking . Change user rights 1.
7.3 Signals in exploratory mode 7.3 Signals in exploratory mode Load a signal curve 1. Click on or MAIN WINDOW / Mode / Exploratory. 2. Click on signal. or EXPLORATORY SPECIFICATION / File / Load 3. Select one or several (Ctrl + Click) signal files *.sig in the OPEN window and click . Save a signal curve 1. Select the desired signal curve in the list of the EXPLORATORY SPECIFICATIONS window. 2. Click on signal. or EXPLORATORY SPECIFICATION / File / Save 3.
7 How to ...? 7. Set pretreatment parameters for electrodes (see Pretreatment, section 3.4). 8. Set Sweep parameters of the selected VA measurement mode (see VA measurement modes, section 3.2). 9. If desired, set Stand-by potential to be applied after measurement (see Stand-by potential, section 3.4). 10.
7.3 Signals in exploratory mode 5. Set the start and end base points for baseline evaluation by clicking the buttons of the Begin or End field. 6. Select Type and Scope of the baseline. 7. Click the button. The calculated baselines and peak maximum positions are displayed in the EXPLORATORY CURVES window. The evaluation results are displayed in the table of results in the EXPLORATORY SPECIFICATION window. Evaluate signal waves 1.
7 How to ...? 7.4 Methods in determination mode Load a method 1. Click on or MAIN WINDOW / Mode / Determination. 2. Click on or MAIN WINDOW / File / Load method. 3. Select the desired method file *.mth in the OPEN window and click . The method is loaded into the WORKING METHOD SPECIFICATIONS window. Copy parameters from determination methods 1. Click on or MAIN WINDOW / Mode / Determination. 2. Click on or MAIN WINDOW / File / Load determination. 3. Select the desired determination file *.
7.4 Methods in determination mode Edit the working method 1. Click on or MAIN WINDOW / Mode / Determination. 2. Click on or MAIN WINDOW / Window / Working method specification to open the WORKING METHOD SPECIFICATIONS window. 3. Click on or MAIN WINDOW / File / Load method. 4. Select the desired method file *.mth in the OPEN window and click . The method is loaded into the WORKING METHOD SPECIFICATIONS window. 5.
7 How to ...? 6. Enable the Measure blank option, enter the number of measurements No. of blanks and the Blank purge time. 7. Close the EDIT WORKING METHOD PARAMETERS window by clicking . If you start a determination with this modified method, you are first asked to place the specified number of blank solutions into the measuring vessel. The resulting blank curve is then automatically subtracted from all subsequent measured curves.
7.5 Determinations 7.5 Determinations Load a determination 1. Click on or MAIN WINDOW / Mode / Determination. 2. Click on or MAIN WINDOW / File / Load determination. 3. Select the desired determination file *.dth in the OPEN window and click . The determination is loaded into the DETERMINATION CURVES window. 4.
7 How to ...? 5. Place the analysis solution in the measuring vessel at the 757 VA Computrace Stand. 6. Click on or MAIN WINDOW / Window / Monitor to open the MONITOR window. 7. Start the measurement by clicking the WINDOW or the icon in the MAIN button in the MONITORING window. 8. Follow the instructions in the appearing message windows.
7.5 Determinations 12. The sample solution spiked with standard addition solution is measured three times. Then the MANUAL ADDITION window appears. 13. Use a pipette to add 100 µLl Pb ion standard solution ρ(Pb) = 1 g/Ll (Metrohm No. 6.2301.100) into the measuring vessel and click the button. 14. The sample solution spiked again with standard addition solution is measured three times. Then the END OF DETERMINATION window appears. 15. Click the button.
7 How to ...? 12. Transfer the desired sample amount into the sample vessels. Place the sample vessels at the odd positions on the sample rack of the 813 Compact Autosampler. For each sample vessel, place a vessel filled with rinsing solution at the following even position (volume rinsing solution = volume sample solution). or MAIN WINDOW / Window / Monitor to open the MONITOR window. 13. Click on 14. Start the measurement by clicking the WINDOW or the icon in the MAIN button in the MONITORING window.
7.5 Determinations 11. Close the EDIT WORKING METHOD PARAMETERS window by clicking . The determination is recalculated and the new results are displayed in the RESULTS window. 12. If desired, repeat steps 10 and 11 once or several times. 13. If you want to save the modified determination under the same name, click on or MAIN WINDOW / File / Save determination. Confirm the question The file already exists. Overwrite? by clicking . 14.
7 How to ...? 7.6 Standard addition technique Use manual standard addition without solution exchange In the manual standard addition without solution exchange, a known amount of the analyte is added once or several times to the sample using a pipette. Proceed as follows: 1. Click on or MAIN WINDOW / Mode / Determination. or MAIN WINDOW / Window / Working method specification to open the WORKING METHOD SPECIFICATIONS window. 2. Click on 3.
7.6 Standard addition technique 15. Enter the Sample ID (used as part of the determination file name) in the PLACE SAMPLE window and click . 16. Each time a standard addition is required in the MANUAL ADDITION window, add the standard addition solution using a pipette. Use manual standard addition with solution exchange In the manual standard addition with solution exchange, a new sample solution is used for every standard addition. Proceed as follows: 1.
7 How to ...? 13. Start the measurement by clicking the WINDOW or the icon in the MAIN button in the MONITORING window. 14. Enter the Sample ID (used as part of the determination file name) in the PLACE SAMPLE window and click . 15. Each time a solution exchange is required in the BATCH SOLUTION EXCHANGE window, replace the measuring solution by the next spiked sample solution.
7.6 Standard addition technique 13. If the standard addition should be done with variable addition volumes, click the button in the Volume column to open the EDIT VARIED ADDITION window, enter the variable addition volumes in the Addition fields, and close this window by clicking . 14. Close the EDIT WORKING METHOD PARAMETERS window by clicking . 15. Place the sample solution in the measuring vessel at the 757 VA Computrace Stand. 16.
7 How to ...? 7.7 Calibration curve technique Record calibration curve manually by adding standard solution This method is used for preparing different calibration solutions by adding several times a concentrated standard solution to the measuring solution using a pipette. Proceed as follows: 1. Click on or MAIN WINDOW / Mode / Determination. or MAIN WINDOW / Window / Working method specification to open the WORKING METHOD SPECIFICATIONS window. 2. Click on 3.
7.7 Calibration curve technique 15. Enter the Calibration curve id (used as part of the determination file name) in the START CALIBRATION window and click . 16. Each time an addition is required in the MANUAL ADDITION window, add the standard solution using a pipette. Record calibration curve manually with solution exchange This method is used for recording a calibration curve using different calibration solutions of known concentration. Proceed as follows: 1.
7 How to ...? 13. Start the measurement by clicking the WINDOW or the icon in the MAIN button in the MONITORING window. 14. Enter the Calibration curve id (used as part of the determination file name) in the START CALIBRATION window and click . 15. Each time a solution exchange is required in the BATCH SOLUTION EXCHANGE window, replace the solution measured by the next calibration solution.
7.7 Calibration curve technique variable addition volumes in the Addition fields, and close this window by clicking . 11. Close the EDIT WORKING METHOD PARAMETERS window by clicking . 12. Place the electrolyte solution (e.g. buffer) in the measuring vessel at the 757 VA Computrace Stand. or MAIN WINDOW / Window / Monitor to open the MONITOR window. 13. Click on 14. Start the measurement by clicking the WINDOW or the icon in the MAIN button in the MONITORING window. 15.
7 How to ...? 10. Start the measurement by clicking the WINDOW or the icon in the MAIN button in the MONITORING window. 11. Enter the Sample ID (used as part of the determination file name) in the PLACE SAMPLE window and click .
7.8 Work with film electrodes 7.8 Work with film electrodes Deposit a mercury film You find a suitable method for the determination of heavy metals with mercury film electrodes in Application Bulletins 241 and 254. 1. Polish the glassy carbon (6.1204.110) or Ultra Trace electrode tip (6.1204.100) with alumina powder (6.2802.000) and put the electrode into the 757 VA Computrace Stand. 2. Put the plating solution into the measuring vessel, e.g.
7 How to ...? 7.9 Diagnostic procedures Check the purging 1. Connect the inert gas to the 757 VA Computrace Stand (see Hardware Manual). 2. Make sure that the inert gas pressure is 1 ± 0.2 bar. 3. Add 20 mL ultrapure water to the empty measuring vessel at the 757 VA Computrace Stand. or MAIN WINDOW / Utility / Computrace control to 4. Click on open the COMPUTRACE CONTROL window. 5. Select HMDE and click on . 6. Make sure that inert gas bubbles are purging through the solution. Check the stirring 1.
7.9 Diagnostic procedures 8. Select SMDE and click on . 9. A small drop is formed and removed in intervals. The drop size has to be reproducible and the drop has to be removed in every interval. 10. If the drop is not removed reproducibly, adjust the tapper mechanism (see Hardware Manual). 11. Select HMDE and click on . 12. A small new drop is formed and stays at the end of the capillary. The drop should remain for at least 1 min.
7 How to ...? Perform a peak test with the dummy cell For testing the peak measurement, the dummy cell of the 757 VA Computrace Stand is used with the test method Test757_D.mth. Proceed as follows: 1. Click on or MAIN WINDOW / Mode / Determination. or MAIN WINDOW / Window / Working method specification to open the WORKING METHOD SPECIFICATIONS window. 2. Click on 3. Click on or MAIN WINDOW / File / Load method. 4. Select the method file Test757_D.mth in the OPEN window and click .
7.9 Diagnostic procedures Perform a GLP test The requirements of GLP (Good Laboratory Practice) include the periodic testing of analytical instruments with regard to reproducibility and accuracy using standard operating procedures. Metrohm suggests the procedure described below as the standard operating procedure for testing the 757 VA Computrace Stand: 1. Click on or MAIN WINDOW / Mode / Determination. 2.
7 How to ...? 15. Use a pipette to add 100 µL Pb ion standard solution ρ(Pb) = 1 g/L (Metrohm No. 6.2301.100) into the measuring vessel and click the button. 16. The sample solution spiked again with standard addition solution is measured three times. Then the END OF DETERMINATION window appears. 17. Click the button. The determination is saved automatically and the result report is printed out. 18.
8.1 General procedure for error messages 8 Troubleshooting 8.1 General procedure for error messages Error messages and warnings are displayed in the CT757 window. Read the information about the possible causes and the procedure for their rectification and click the button. 8.2 Connection problems Error message "Could not start the embedded system" If this error message appears after starting the VA Computrace program, the VA Computrace Interface is not running properly. Proceed as follows: 1.
8 Troubleshooting 8.3 Software problems Error message "No access to software" If the login fails because no password is known any more, proceed as follows: 1. Deinstall the software (see Deinstallation, section 1.3). 2. Reinstall the software (see Software installation, section 1.3). Error message "The file 'ecousb.sys' is needed" This message indicated problems with the USB connection. Proceed as follows: 1. Insert the installation CD into the CD drive. 2. Click on .
8.4 Dosimat problems Irreproducible standard additions with 765 Dosimat 1. Click on or MAIN WINDOW / Utility / Dosimat control to open the DOSIMAT CONTROL window (see Dosimat control window, section 6.2). 2. Select the desired Dosimat in the Burette field. 3. Click the button to empty and refill the exchange unit installed on the Dosimat. 4. Check if there are air bubbles left in the glass cylinder of the exchange unit. If this is the case, repeat the flushing procedure by clicking the button. 5.
8 Troubleshooting 8.5 General rules for VA trace analysis Chemicals and equipment 1. The purity of the reagents plays an important role in determining the results. Extremely pure chemicals should be used for determining lower concentrations (see VA Application Note V49). 2. Measuring vessel, electrodes and all other equipment in contact with the sample solution must be clean and free of contamination substances. Electrolytes 1. The pH during a determination plays an important role (e.g.
8.5 General rules for VA trace analysis Samples 1. The amount of sample depends on the concentration of the element to be determined. 2. If the sample matrix is known, a better assessment of the analysis can be made (organic components?). 3. A digestion must be carried out on contaminated samples and on samples where contamination is suspected (see Metrohm Monograph «Sample preparation for techniques in voltammetric trace analysis»). 4. A lot of errors are made during sampling and when storing the sample.
8 Troubleshooting Selection of VA Measurement mode The following points should be considered by selecting the VA measurement mode: 1. DP (Differential Pulse) should be always the first choice. It is the most universal and frequently used voltammetric determination method and is equally well suited for reversible and irreversible systems. It offers a high sensitivity down to 10–8 mol/L and a separation ability of 1:50'000. 2.
8.6 Voltammetric problems 8.6 Voltammetric problems Low background current or unstable baseline With all types of electrodes: 1. Check electrolyte concentration and pH of the solution. 2. Check Start potential and End potential of the sweep. 3. If the ion concentration in the solution is too high: dilute the electrolyte. 4. Has the sample been degassed? Degassing with nitrogen for at least 5 min is recommended, for alkaline solutions approx. 10 min is recommended. 5.
8 Troubleshooting 4. Has the electrode been conditioned (e.g. by using Conditioning cycles and Cleaning potential) ? 5. If the concentration to be determined is considerably higher than expected: reduce sample volume. 6. The background current is normally higher if RDE is used in place of MME; a background current of several 100 nA is possible. Curves with high noise With all MME types: 1. Have stirring or degassing been switched off during the measurement? 2. Check contact between needle and capillary.
8.6 Voltammetric problems Standard addition curves are not reproducible With all types of electrodes: 1. Check method parameters (stirring time, etc.). 2. Check and test the pipetting process: Pipetting the standard solutions must be carried out by one and the same person or with the same instrument or the same pipette. Was the pipetting unit used properly? When were the pipettes last calibrated (GLP)? 3.
8 Troubleshooting No peak found With all types of electrodes: 1. The peak is only displaced: adjust the half-wave potential and recalculate the results. 2. The sample concentration is too low: increase the sample volume or the amount of sample. 3. Are the Start potential and End potential correct? 4. Electrolyte solution too old: make up a new one. Its working life with organic additives may be as short as 1 day or less. 5.
8.6 Voltammetric problems With RDE/SSE: 1. The background current is too high: repolish the electrode. 2. The Deposition time is too long: reduce the time. 3. Is the Deposition potential correct? Double peak With all types of electrodes: 1. Organic components interfere with the analysis: carry out a UV digestion or other suitable sample preparation. 2. Electrolyte solution too old: make up a new one. Its working life with organic additives may be as short as 1 day or less. 3.
8 Troubleshooting Standard addition peaks displaced With all types of electrodes: 1. Standard solutions have been made too acidic. 2. Buffering capacity of the electrolyte is not sufficient: increase electrolyte volume. 3. Electrolyte solution too old: make up a new one. Its working life with organic additives may be as short as 1 day or less. With HMDE: 1. If HMDE is used potential displacements of more than 20…30 mV are often normal and have to be accepted; particularly in adsorption voltammetry.
8.6 Voltammetric problems Oxygen interference Oxygen can be electrochemically reduced and produces two waves in the voltammogram, one of which is characterized by the appearance of a pronounced maximum. The oxygen reduction can interfere for two reasons: • The signals of the analytes are masked by the oxygen waves. This becomes noticeable primarily in trace analysis as the oxygen is present in a relatively high concentration in solutions saturated with air (ca. 8 mg/L at room temperature).
8 Troubleshooting Overcharging of the working electrode Under unfavorable conditions (high concentrations and/or long enrichment times), the enrichment of species at polarized electrodes leads to overcharging phenomena such as non-linear standard addition curves or splitting into multiple peaks which are caused by saturation and different deposition forms. A shorter enrichment time usually solves the problem.
8.6 Voltammetric problems • Mercury determination at the gold electrode On prolongation of the enrichment time from 30 s to 240 s, side peaks appear during standard addition: Enrichment time: 30 s Enrichment time: 240 s Hg Hg Analysis solution: Supporting electrolyte: Standard addition: Electrode: 100 µg/L Hg HClO4/HCl with 1 µg Hg Au-RDE Disturbances at the HMDE through gas formation Gas formation at the HMDE during the deposition phase can lead to drop fall or to a contact break in the Hg capillary.
8 Troubleshooting Supporting electrolyte: 0.01 mol/L HClO4; pH = 2 Zn Analysis solution: Standard addition: Electrode: Supporting electrolyte: acetate buffer pH = 4.64 Zn deionised water with 50 ng Zn HMDE (enrichment 60 s at –1.2 V) Complex formation Substances determined polarographically can occur in various complexed forms, depending on the composition of the analysis solution.
8.6 Voltammetric problems mL analysis solution] would also give a clearly defined current peak for CuCl2–.) Supporting electrolyte: without EDTA Supporting electrolyte: with EDTA (0.
8 Troubleshooting Peak overlapping If the peak overlapping has reached a critical level at which the calculated peak height or peak area is falsified by the neighbouring peak, it is advisable to take the overlapping into account by a change in the baseline calculation. For this, select the Front end or Rear end option for the baseline Scope (see Baseline, section 5.2). If the overlapping is too large, the peak can no longer be evaluated.
8.6 Voltammetric problems Calibration with chemically non-isoformal standards With both possible calibration techniques, it must be ensured that the standards used for calibration are chemically isoformal with the analytes. The standard substances must therefore have the same valency (e.g. with Fe, Al) or complex formation form (e.g. with As, Cr, Se) as the substances already present in the analysis solution.
8 Troubleshooting 180 757 VA Computrace – Software
Software license Software license The use of the Software is subject to this License Agreement between you and Metrohm AG. With the offer, you have received this License Agreement and taken note of it. You have already accepted this License Agreement upon the placement of your order with Metrohm AG or one of its distributors or upon confirmation of the order by Metrohm or one of its distributors.
Software license 6. This Agreement applies until it is terminated. You can terminate this Agreement by destroying the Software and every copy of it. The Agreement is also deemed terminated if you violate any of its terms, in which case you are also obligated to destroy the Software and every copy of it, whereby Metrohm is also entitled to explicitly demand this of you. 7. Any changes and amendments to this Agreement must be rendered in writing to attain validity.
Index Index A Absolute substance mass .................................105 AC..................................................................43,166 Added mass.......................................................105 Addition purge time..............................................76 Addition volume ..............................................79,84 Add-on board Data transfer ................................................113 Hardware installation .......................................
Index Contamination ................................................... 165 Content calculation ............................................ 117 Context sensitive menus...................................... 10 Continue determination ....................................... 89 Continue measurement ....................................... 59 Copy Copy parameters from determination methods......................... 138 Copy parameters from signal files .............. 138 Copy parameters to working method ........
Index E Edit Edit baseline ..................................................98 Edit determination method parameters ........96 Edit parameters .............................................75 Edit peak ........................................................67 Edit working method....................................139 Electrochemical enrichment.................................47 Electrochemical regeneration .......................47,129 Electrodes ...................................
Index Load Load determination ................................ 94,141 Load method .......................................... 72,138 Load signal curves ................................. 60,135 Login ............................................................... 13,17 Low background current ................................... 167 Lowest current range........................................... 45 M Main window Closing .......................................................... 13 Elements.....................
Index Predose ................................................................87 Preparation procedures .......................................45 Pretreatment.........................................................47 Printer setup .........................................................16 Printing .................................................................16 Automatic documentation printout ................85 Determination...............................................
Index Software license................................................. 181 Software upgrade .................................................. 5 Solid state electrode .........................30,47,128,130 Solutions ............................................................ 106 Specifications tab ................................................ 96 Spikes ................................................................ 172 Square wave voltammetry ................................... 33 SqW.................
