Flow-through amperometric measuring system and method

• US 3,902,970 A
• Filed: 07/30/1973
• Issued: 09/02/1975
• Est. Priority Date: 07/30/1973
• Status: Expired due to Term

• Current Assignee: Herman W. Levin
• Original Assignee: Herman W. Levin
• Inventors: Levin, Herman W.
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US05/383,855
• Time in Patent Office: 764 Days
• Field of Search: 204/195B,195R,1T 195/13.5R,13.5C 23/23R,23B,253R 324/29
• US Class Current: 205/777.5
• CPC Class Codes: G01N 27/3271 Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood amperometry per se G01N27/49; aspects concerning the enzyme reagent C12Q1/001

Abstract

An amperometric measuring system for measuring the concentration of glucose in solution is disclosed. This system uses the enzyme glucose oxidase immobilized on glass beads to convert a continuously drawn sample to hydrogen peroxide and gluconic acid. A flow-through amperometric cell with a small bore flow path is provided to measure the concentration of hydrogen peroxide. The cell includes a cylindrical measuring electrode which carries the sample through its relatively long narrow bore, a counter electrode and a reference electrode interposed between the measuring and counter electrodes with a differential amplifier for automatically adjusting the current between the measuring and counter electrodes to maintain the potential between the measuring and reference electrode at a predetermined value as fed to one input of the amplifier. The current from the measuring electrode is measured as an indication of the concentration of hydrogen peroxide in the solution and hence the glucose concentration.

Claims

1. A METHOD FOR AMPEROMETRICALLY ANALYZING A SAMPLE OF A SOLUTION OF AN ELECTROINACTIVE UNKNOWN TO DETERMINE ITS CONCENTRATION WITHOUT USING A SECONDARY REAGENT, COMPRISING THE STEPS OF:

ENZYMATICALLY CONVERTING THE INACTIVE UNKNOWN BY FLOWING THE SAMPLE THROUGH A BED OF BEADS TO WHICH IS BONDED AN ENZYME WHICH SELECTIVELY REACTS WITH SAID UNKNOWN TO PRODUCE HYDROGEN PEROXIDE AS ONE BYPRODUCT, FLOWING THE RESULTING BYPRODUCTS THROUGH AN AMPEROMETRIC CELL HAVING, A MEASURE ELECTRODE, A COUNTER ELECTRODE, AND A REFERENCE ELECTRODE, AUTOMATICALLY MAINTAINING A CURRENT FLOW BETWEEN SAID MEASURING AND COUNTER ELECTRODES SO AS TO MAINTAIN A CONSTANT POTENTIAL BETWEEN THE MEASURING AND REFERENCE ELECTRODES, AND MEASURING SAID CURRENT FLOW AS AN INDICATION OF THE CONCENTRATION OF HYDROGEN PEROXIDE IN SAID BYPRODUCTS AND HENCE THE CONCENTRATION OF SAID ELECTROINACTIVE UNKNOWN IN SAID SAMPLE SOLUTION.

2. The method as set forth in claim 1 in which the reference electrode is positioned so that the counter electrode and the reference electrode are on the same side of the measuring electroDe.

3. A MEASURING SYSTEM FOR CONTINUOUSLY ANALYZING A SAMPLE OF A GLUCOSE SOLUTION TO DETERMINE ITS CONCENTRATION, COMPRISING:

MEANS FOR CONTINUOUSLY DRAWING THE SAMPLE OF SAID SOLUTION, MEANS FOR ENZYMATICALLY CONVERTING THE GLUCOSE IN SAID SOLUTION TO HYDROGEN PEROXIDE AND GLUCONIC ACID, SAID MEANS INCLUDING A FLOW-THROUGH COLUMN OF BEADS HAVING THE ENZYME GLYCOSE OXIDASE IMMOBILIZED ON THEIR SURFACE, SAID COLUMN CONTAINING SUFFICIENT ENZYME TO CAUSE THE REACTION BETWEEN SAID ENZYME AND SAID GLUCOSE TO GO TO COMPLETION IN SAID COLUMN, MEANS FOR FLOWING THE RESULTING SOLUTION THROUGH AN AMPEROMETRIC CELL WHICH INCLUDES, A VITREOUS CARBON MEASURING ELECTRODE ADAPTED TO BE IN CONTACT WITH SAID RESULTING SOLUTION ALONG THE FLOW PATH, A COUNTER ELECTRODE ADAPTED TO BE IN CONTACT WITH SAID RESULTING SOLUTION ALONG THE FLOW PATH, AND A REFERENCE ELECTRODE POSITIONED TO BE IN CONTACT WITH SAID RESULTING SOLUTION ALONG SAID PATH, MEANS FOR AUTOMATICALLY MAINTAINING A CURRENT FLOW BETWEEN SAID MEANS A CONSTANT POTENTIAL BETWEEN THE MEASURING AND REFERENCE ELECTRODES, AND MEANS FOR MEASURING SAID CURRENT FLOW AS AN INDICATION OF THE CONCENTRATION OF HYDROGEN PEROXIDE PRODUCED BY SAID CONVERSATION AND HENCE THE CONCENTRATION OF GLUCOSE IN SAID SAMPLE SOLUTION.

4. A measuring system for continuously analyzing a sample of a glucose solution to determine its concentration, comprising:

means for continuously drawing a sample of said solution;

means for enzymatically converting the glucose in said solution to hydrogen peroxide and gluconic acid, said converting means including a flow-through column of beads having the enzyme glucose oxidase immobilized on their surface so that the column contains sufficient enzyme to cause the reaction between said enzyme and said glucose solution to go to completion in said column;

means for flowing the resulting solution through an amperometric cell which includes;

a vitreous carbon measuring electrode adapted to be in contact with said resulting solution, a counter electrode adapted to be in contact with said resulting solution, and a reference electrode positioned along the flow path to be in contact with said resulting solution so that the measuring electrode is outside an electric current path between the counter electrode and reference electrode;

means for automatically maintaining a current flow between said measuring and counter electrodes so as to maintain a constant potential between the measuring and reference electrodes; and

means for measuring said current flow as an indication of the concentration of hydrogen peroxide produced by said conversion and hence the concentration of glucose in said sample solution.

5. A measuring system as set forth in claim 4 in which the reference electrode has a liquid junction formed to be flush with the walls forming the flow path.