Apparatus for use in rapid and accurate controlled-potential coulometric analysis

• US 4,244,800 A
• Filed: 08/23/1979
• Issued: 01/13/1981
• Est. Priority Date: 08/23/1979
• Status: Expired due to Term

• Current Assignee: United States Of America As Represented By The Department Of Energy
• Original Assignee: United States Department of Energy (Government of the United States of America)
• Inventors: Pietri, Charles E., Frazzini, Thomas L., Weiss, Jon R., Holland, Michael K.
• Primary Examiner(s): Tung, T.
• Application Number:
  US06/069,152
• Time in Patent Office: 509 Days
• Field of Search: 204/1 T, 204/195 R, 204/1 M, 204/195 T
• US Class Current: 204/406
• CPC Class Codes: G01N 27/423 Coulometry

Abstract

An apparatus for controlled-potential coulometric analysis of a solution includes a cell to contain the solution to be analyzed and a plurality of electrodes to contact the solution in the cell. Means are provided to stir the solution and to control the atmosphere above it. A potentiostat connected to the electrodes controls potential differences among the electrodes. An electronic circuit connected to the potentiostat provides analog-to-digital conversion and displays a precise count of charge transfer during a desired chemical process. This count provides a measure of the amount of an unknown substance in the solution.

Claims

1. In an apparatus for controlled-potential coulometric analysis of an electroactive species in a solution, including a cell containing the solution, means for supplying a controlled atmosphere in the cell, means for stirring the solution in the cell, a working electrode disposed in the cell in electrical contact with the solution, a counter electrode disposed in the cell in electrical contact with the solution, a reference electrode disposed in the cell in electrical contact with the solution, a potentiostat connected to the working electrode, the counter electrode and the reference electrode for applying controlled electrical potential differences between the working electrode and the reference electrode and between the counter electrode and working electrode, an improved means for obtaining a digital electrical equivalent to electric current flow through the solution, the improvement comprising:

a first scaler connected to an output of the potentiostat and receiving an electrical signal from the potentiostat that is proportional to current through the working electrode;

a first voltage-to-frequency converter connected to the first scaler and receiving as an input a scaled signal from the first scaler, and producing a digital readout signal;

a first zero adjust connectable to a power supply and to the first voltage-to-frequency converter to provide a scaled zero input signal to the first voltage-to-frequency converter;

a second voltage-to-frequency converter;

a second zero adjust connectable to a power supply and connected to provide a zero input to the second voltage-to-frequency converter;

a second scaler connectable to the readout signal and to electrical ground and connected to the second voltage-to-frequency converter to produce a digital zero-output signal;

a clock producing an electrical signal at a fixed frequency; and

a display card connected to the means for obtaining and displaying visually a count that is proportional to a current flow through the solution.

2. The apparatus of claim 1 wherein said display card is connected to provide a visual digital indication of the digital readout signal, the digital zero output signal and the clock signal.

3. The apparatus of claim 2 comprising in addition means connectable electrically to the potentiostat to produce alignment signals.

4. The apparatus of claim 3 comprising in addition means for resetting the display card to begin a measurement.

5. In an apparatus for controlled-potential coulometry in which an electrostatic species is disposed in a cell containing electrodes and in which a voltage control means is connected to the electrodes to apply to them controlled voltages, an improved converter means connected to the voltage control means for converting a voltage proportional to current flow in the cell to a digital signal, the improvement comprising:

a first integrator means having first and second input means, means for adding signals received by said first and said second input means, said first input means receiving an electrical signal from said voltage control means that is proportional to current flow in the cell, said second input means receiving a predetermined offset signal,

a second integrator means connected to said offset signal producing a digital readout signal; and

a display card connected to said first and second second integrator means for displaying a count proportional to current flow in the cell.

6. The apparatus of claim 5 wherein said voltage control means comprises a potentiostat.

7. The apparatus of claim 5 wherein said first integretor means comprises a first voltage-to-frequency converter.

8. The apparatus of claim 7 wherein said first voltage-to-frequency converter has a voltage input and a current input.

9. The apparatus of claim 7 wherein said second integrator means comprises a second voltage-to-frequency converter.

10. The apparatus of claim 9 wherein said second voltage-to-frequency converter has first and second inputs, said first input connected to said offset signal, and said second input selectively receiving an alignment signal.