Detection circuitry for electrochemical analysis

• US 4,426,621 A
• Filed: 06/29/1981
• Issued: 01/17/1984
• Est. Priority Date: 06/29/1981
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Kanazawa, Kay K., Galwey, Ronald K.
• Primary Examiner(s): Tokar, Michael J.
• Assistant Examiner(s): O'Shea, Kevin D.
• Application Number:
  US06/278,801
• Time in Patent Office: 932 Days
• Field of Search: 324/439, 324/446, 324/438, 204/406, 204/412
• US Class Current: 324/439
• CPC Class Codes: G01N 27/49 Systems involving the determination of the current at a single specific value, or small range of values, of applied voltage for producing selective measurement of one or more particular ionic species

Abstract

Analytical apparatus is arranged for increased sensitivity in determining a desired characteristic by decreasing the sensitivity to extraneous noise, essentially as common mode signal, while treating the desired signal differentially. Test signal is applied to apparatus comprising an electrochemical cell containing electrolyte in which a pair of matched working electrodes are equispaced from a counter electrode and from a reference electrode. The working electrodes conduct different values of current, the difference being a measure of characteristic of material making up the electrolyte. The signal applied between the counter and the working electrodes is varied over a predetermined range. The potential between the working electrodes is established at zero for basic operation, but a fixed biasing potential is established between the two working electrodes for a given experiment in which the test signal is varied. The biasing potential is usually relatively small and the current flow difference under study is likewise very small. The data output signal which is proportional to the small difference in the currents, is amplified in stable high gain circuitry.

Claims

1. In combination, an electrochemical cell having a receptacle for electrolyte, electrodes arranged in said electrolyte including:

a counter electrode, a reference electrode, and two working electrodes;

a pair of test signal input terminals, one of which is connected to a fixed reference potential;

an input differential amplifier circuit having an output connected to said counter electrode, one input connected to said reference electrode, and another input connected to said other test signal input terminal;

a signal detection circuit including;

first and second differential amplifying circuits each having a first input terminal, a second input terminal and an output terminal;

an output differential amplifier having a pair of input terminals and an output terminal;

means connecting the output terminals of said first and second amplifying circuits to a different one of said pair of input terminals of said output differential amplifier;

means connecting said first input terminal of each said first and second differential amplifying circuit to a different said working electrode;

means connecting said second input terminal of one of said first and second amplifying circuits to said reference potential; and

means, including a potentiometer, for connecting said second input terminal of the other of said first and second differential amplifying circuits and the other input terminal of said pair of input terminals of said output differential amplifier to said reference potential whereby the signals supplied to said output differential amplifier may be varied relative to each other by said potentiometer independently of the currents supplied to said first and second amplifying circuits from said respective working electrodes when said test signal is applied to said test signal input terminals to permit detecting any difference in currents passing between said electrolyte and said working electrodes, which difference represents a characteristic of an electroactive species in a test sample added to said electrolyte.

2. In combination, an electrochemical cell having a receptacle for electrolyte, electrodes arranged in said electrolyte including:

a counter electrode, a reference electrode, and two working electrodes;

a pair of test signal input terminals, one of which is connected to a fixed reference potential

an input differential amplifier circuit having an output connected to said counter electrode, one input connected to said reference electrode, and another input connected to said other test signal input terminal;

an output differential amplifier having a pair of input terminals and an output terminal for providing an output signal which is proportional to the difference of the signal supplied to said input terminals; and

means for supplying to said input terminals of said output differential amplifier signals from said working electrodes developed during application of said test signal to said test input terminals, said means for supplying including means for biasing one of said working electrodes relative to said reference electrode differently than said other working electrode is biased relative to said reference electrode to cause the current signals supplied from said working electrodes to be different for each value of said test signal to thereby provide a detectable signal at the output terminal of said output differential amplifier which reflects a characteristic of an electroactive species in said electrolyte.