High sensitivity multiple waveform voltammetric instrument
First Claim
1. A multiple waveform voltammetric instrument comprising:
- a signal generator means for generating a command signal including pulses superimposed on a DC bias potential, the generator means including means for selectively inverting the pulses, and means for selecting a DC level of the DC bias potential;
a potentiostat having an input for receiving the command signal, first, second and third instrument terminals, and regulating means for applying, between the first and second instrument terminals, a potential difference corresponding substantially to the command signal;
means for grounding the third instrument terminal and producing an output signal indicative of a current flowing through the third instrument terminal;
an integrator means for integrating the output signal to produce an integrated response signal, the integrator means including means for selectively inverting the output signal prior to integration, and means for resetting the integrated response signal; and
control means for time-controlling generation and inversion of the pulses, the DC level of the DC bias potential, inversion and integration of the output signal and resetting of the integrated response signal, according to a selected voltammetric mode of operation.
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Abstract
A high sensitivity multiple waveform voltammetric method and instrument are provided for use in electrochemical and other applications. The method consists of applying one or several variable potential excitation signals between electrodes of an electrochemical cell to produce an electrochemical reaction in the solution. The excitation signals include a DC bias potential increasing cyclically by a potential step to form a potential staircase signal sweeping across a potential domain, and a number of pulse trains either of opposite polarity or shifted in potential per potential step. An electric current derived from a diffusion flux of ions through the solution is measured as a result of the applied excitation signal. The instrument is adapted to perform the method, and is provided with an accurate and low noise signal generator circuit, a circuit for reducing a double layer capacitive effect in the cell, a potentiostat having a virtual mass counter electrode, a feedback circuit for compensating an ohmic drop in the cell, and an integrator circuit for integrating the current signal produced by the cell.
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Citations
36 Claims
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1. A multiple waveform voltammetric instrument comprising:
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a signal generator means for generating a command signal including pulses superimposed on a DC bias potential, the generator means including means for selectively inverting the pulses, and means for selecting a DC level of the DC bias potential; a potentiostat having an input for receiving the command signal, first, second and third instrument terminals, and regulating means for applying, between the first and second instrument terminals, a potential difference corresponding substantially to the command signal; means for grounding the third instrument terminal and producing an output signal indicative of a current flowing through the third instrument terminal; an integrator means for integrating the output signal to produce an integrated response signal, the integrator means including means for selectively inverting the output signal prior to integration, and means for resetting the integrated response signal; and control means for time-controlling generation and inversion of the pulses, the DC level of the DC bias potential, inversion and integration of the output signal and resetting of the integrated response signal, according to a selected voltammetric mode of operation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. An accurate and low noise signal generator circuit for a potentiostat in a voltammetric instrument, the signal generator circuit comprising:
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a pulse generator means for generating a command signal including pulses; an active low pass filter connected to the pulse generator, the low pass filter including an amplifier combined with a resistor-capacitor feedback circuit to give the low pass filter a long time constant to filter noise and stabilize the command signal for transmission to the potentiostat; and means for injecting a correcting charge in the capacitor of the low pass filter during pulse transitions in the command signal, to compensate an effect of the time constant of the low pass filter on rise and fall times of the pulses in the command signal. - View Dependent Claims (29, 30)
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31. A circuit for reducing a double layer capacitive effect in an electrochemical cell having a pair of electrodes subjected to a potential difference produced by a potentiostat in response to a command signal including pulses corresponding to the potential difference to be produced, the circuit comprising:
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a summing circuit having a first input for receiving the command signal, a second input for receiving impulses, and an output for superimposing the impulses onto the command signal; an amplifier having an input connected to the input of the summing circuit, and an output; an adjustable differentiator having an input connected to the output of the amplifier, and an output; and an adjustable attenuator having an input connected to the output of the differentiator, and an output to produce the impulses.
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32. A potentiostat connected with an electrochemical cell having reference, working and counter electrodes, the potentiostat comprising:
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an input for receiving a command signal corresponding to a potential difference to be applied between the working and reference electrodes, first, second and third instrument terminals connected with the reference, working and counter electrodes, respectively; regulating means for applying the potential difference between the working and reference electrodes, the regulating means having a first input connected to the input of the potentiostat to receive the command signal, a second input connected to the first instrument terminal to receive a reference potential of the reference electrode, and an output connected to the second instrument terminal to apply an excitation potential on the working electrode, the excitation potential resulting from an addition of the reference potential with the command signal, thereby producing the potential difference between the working and reference electrodes; and means for grounding the third instrument terminal and producing an output signal indicative of a current flowing through the third instrument terminal. - View Dependent Claims (33)
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34. A feedback circuit for compensating an ohmic drop in an electrochemical cell having a pair of electrodes subjected to a pulsed potential difference, and a grounded electrode in which current flows in response to the pulsed potential difference, the feedback circuit comprising:
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a current to voltage converter having an input connected to the grounded electrode, and an output to produce a voltage signal as a function of the current; a switch responsive to a switch signal, the switch having an input connected to the output of the current to voltage converter, and an output to transmit the voltage signal depending on the switch signal; control means for producing the switch signal to close the switch for a predetermined time period during transitions of the pulsed potential difference, and to open the switch outside the time period; a summing circuit for adding the voltage signal transmitted by the switch to the pulsed potential difference applied between the pair of electrodes.
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35. A digital integrator arrangement for integrating a current signal produced by an electrochemical cell subjected to a pulsed potential difference, comprising:
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a current to voltage converter having an input for receiving the current signal, and an output to produce a voltage signal indicative of the current signal; a digital integrator having; an input connected to the output of the current to voltage converter; a voltage to frequency converter having an input connected to the input of the integrator, and an output to produce a pulsed signal having a frequency indicative of a voltage value of the voltage signal; an UP/DOWN counter means for counting pulses in the pulsed signal to produce an output count signal, the counter means having an UP/DOWN input to receive an UP/DOWN control signal affecting a counting direction of the pulses in the pulsed signal, and a reset input to receive a reset signal causing the counter means to reset the output count signal; comparator means for comparing the voltage signal with a reference signal selected to determine a polarity of the voltage signal, and producing a signal indicative of the polarity; and logic circuit means for producing the UP/DOWN control signal depending on the polarity of the voltage signal as determined by the comparator means; and control means having an output to produce the reset signal at predetermined times according to a selected voltammetric mode of operation. - View Dependent Claims (36)
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Specification