Flow-compensated electrochemical cell and method of analysis

• US 4,908,105 A
• Filed: 02/15/1985
• Issued: 03/13/1990
• Est. Priority Date: 02/15/1985
• Status: Expired due to Fees

• Current Assignee: Hydrolab Corporation (Danaher Corporation)
• Original Assignee: Hydrolab Corporation (Danaher Corporation)
• Inventors: Garner, William Jr.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/703,677
• Time in Patent Office: 1,852 Days
• Field of Search: 204/411, 204/412, 204/415, 204/403, 204/1 P, 204/414, 204/406, 128/635
• US Class Current: 205/782.5
• CPC Class Codes: G01N 27/404 Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid , e.g. Clark-type oxygen sensors

Abstract

A method and an apparatus for measuring concentration of a dissolved substance are disclosed. In accordance with the method, measurements are made with two instruments having different permeability characteristics to obtain two readings, and these readings are corrected in accordance with a pre-determined relationship. The apparatus provides an electrochemical cell wherein a common anode is surrounded by closely-spaced cathodes. The cathodes are in at least two groups, wherein the first group has a first response characteristic to the dissolved substance and the second group has a second response characteristic. In the preferred embodiment, the two characterisitcs are produced by providing different distances between a substance-selective membrane and respective cathodes. In one embodiment, the cathodes are annular and surround the anode at different radii, while in another embodiment the cathodes are discrete and are spaced from the anode by equal distances.

Claims

1. An instrument for chemical analysis comprising body means for supporting a first electrode having a first polarity and a plurality of second electrodes having a second polarity with respect to said first electrode, and electrolyte means for passing electrical current between said first and second electrodes wherein the rate of passage of a substance to at least one of said second electrodes is different from the rate of passage of said substance to another of said second electrodes, and computation means connected to said first and second electrodes for combining signals from each of said second electrodes and correcting said signals to produce a single flow-insensitive output representative of said substance.

2. A method for chemical analysis comprising providing a first electrochemical cell for measuring concentration of a substance in a medium and having a first flow sensitivity to the velocity of flow of said medium past said first cell and a second electrochemical cell for measuring the concentration of said substance in said medium and having a second flow sensitivity to the velocity of flow of said medium past said second cell, placing said first and second cells in said medium in close proximity to each other and combining values representative of the concentration of the substance produced by each of said cells to provide a measurement of said concentration which is not sensitive to said velocity of flow.

3. A method according to claim 2 wherein said first electrochemical cell and said second electrochemical cell have a common anode.

4. A method according to claim 2 wherein said step of using values from each of said cells comprises the step of modifying said values by a value derived from the ratio of the values from each cell as well as the ratio of the zero boundary layer values for each of the cells.

5. A method for analysis of a flowing medium comprising providing a first measurement means for measuring a quantity of said medium and having a first flow sensitivity to the velocity of flow of said medium and a second measurement means for measuring said quantity in said medium and having a second flow sensitivity to said velocity of flow of said medium, placing said first and second measurement means in close proximity to each other, and combining the measured values of said quantity produced by said first and second measurement means to determine the actual amount of said quantity.

6. A method for measuring the concentration of a dissolved substance in a sample comprising providing an electrochemical cell comprising a first electrode of one polarity, second and third electrodes at an opposite polarity, and a membrane for passing said substance from said sample to said electrodes, said second and third electrodes being so positioned that said substance travels at different rates to each of said second and third electrodes, said method further comprising measuring the electrical current through each of said second and third electrodes to produce signals representative of said concentration and combining and correcting said signals in accordance with a calibration value to produce a measurement of said concentration.

7. A method according to claim 6 wherein said calibration value is a function of the ratio of zero boundary layer signals for said electrodes.