Combined pH and dissolved carbon dioxide gas sensor
First Claim
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1. An apparatus for measuring pH and the concentration of dissolved CO2 in a fluid comprising:
- a measurement chamber for containing a sample of fluid to be measured;
a pH sensor includinga first wire having first and second ends, said first end exposed for electrical contact thereto,a first electrochemically active layer disposed covering said second end of said first wire for forming an electrochemical coupling to said first wire,a first dried electrolyte layer disposed covering said first electrochemically active layer, said first dried electrolyte layer when hydrated forming an aqueous solution buffered against changes in pH due to changes in dissolved CO2 concentration, anda first membrane having an outer surface exposed to the fluid in the said measurement chamber and an inner surface covering said first electrolyte layer, said first membrane being sensitive to the difference in pH between the inner and outer surfaces thereof to form an electrical potential thereacross and being water permeable;
a CO2 sensor includinga second wire having first and second ends, said first end exposed for electrical contact thereto,a second electrochemically active layer disposed covering said second end of said second wire for forming an electrochemical coupling to said second wire,a second dried electrolyte layer disposed covering said second electrochemically active layer, said second dried electrolyte layer when hydrated forming an aqueous solution including bicarbonate ions, anda second membrane having an outer surface exposed to the fluid in said measurement chamber and an inner surface covering said second electrolyte layer, said second membrane being sensitive to the difference in pH between the inner and outer surfaces thereof to form an electrical potential thereacross and being water and dissolved CO2 permeable;
a ground electrode disposed in electrical contact with the fluid in said measurement chamber;
a reference electrode disposed in electrical contact with the fluid in said measurement chamber for providing a stable reference potential independent of ionic activity of the fluid in said reference chamber; and
an electrical circuit connected to said first ends of said first and second wires includinga first differential signal means connected to said first wire and said ground electrode for generating a first difference signal proportional to the electrical potential difference between said first wire and said ground electrode,a second differential signal means connected to said second wire and said ground electrode for generating a second difference signal proportional to the electrical potential difference between said second wire and said ground electrode,a third differential signal means connected to said reference electrode and said ground electrode for generating a third difference signal proportional to the electrical potential difference between said reference electrode and said ground electrode,a fourth differential signal means connected to said first differential signal means and said third differential signal means for generating a fourth difference signal proportional to the electrical potential difference between said first difference signal and said third difference signal, said fourth difference signal being said pH signal,a fifth differential signal means connected to said second and third differential signal means for generating a fifth difference signal proportional to the electrical potential difference between said second difference signal and said third difference signal, anda sixth differential signal means connected to said fourth differential signal means and said fifth differential signal means for generating a sixth difference signal proportional to the electrical potential difference between said fourth difference signal and said fifth difference signal, said sixth difference signal being said CO2 signal.
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Abstract
A combination pH and CO2 sensor employs separate sensors. Each sensor has a wire with an electrochemically active layer, an electrolyte layer and a membrane between the electrolyte layer and the fluid to be tested. Each electrolyte layer is constructed of a dried residue which can be easily stored and which must be rehydrated prior to the first use. The electrolyte layer in the pH sensor when hydrated forms an aqueous solution buffered against changes in pH due to changes in the dissolved CO2 concentration and is preferably formed of 2-(n-morpholino) ethanesulfonic acid, 2-(n-morpholino) ethanesulfonic acid - sodium salt and potassium chloride. The electrolyte layer in the CO2 sensor when hydrated forms an aqueous solution having bicarbonate ions and is preferably formed of polyvinyl alcohol, sodium chloride and sodium bicarbonate. The electrical potential at the pH sensor is proportional to the pH of the fluid. The electrical potential difference between the CO2 sensor and the pH sensor is proportional to the concentration of dissolved CO2 in the fluid. In the preferred embodiment the two sensors are formed in a sensor assembly with the fluid pumped through a channel. This invention is readily adaptable to a storage stable disposable assembly.
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Citations
16 Claims
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1. An apparatus for measuring pH and the concentration of dissolved CO2 in a fluid comprising:
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a measurement chamber for containing a sample of fluid to be measured; a pH sensor including a first wire having first and second ends, said first end exposed for electrical contact thereto, a first electrochemically active layer disposed covering said second end of said first wire for forming an electrochemical coupling to said first wire, a first dried electrolyte layer disposed covering said first electrochemically active layer, said first dried electrolyte layer when hydrated forming an aqueous solution buffered against changes in pH due to changes in dissolved CO2 concentration, and a first membrane having an outer surface exposed to the fluid in the said measurement chamber and an inner surface covering said first electrolyte layer, said first membrane being sensitive to the difference in pH between the inner and outer surfaces thereof to form an electrical potential thereacross and being water permeable; a CO2 sensor including a second wire having first and second ends, said first end exposed for electrical contact thereto, a second electrochemically active layer disposed covering said second end of said second wire for forming an electrochemical coupling to said second wire, a second dried electrolyte layer disposed covering said second electrochemically active layer, said second dried electrolyte layer when hydrated forming an aqueous solution including bicarbonate ions, and a second membrane having an outer surface exposed to the fluid in said measurement chamber and an inner surface covering said second electrolyte layer, said second membrane being sensitive to the difference in pH between the inner and outer surfaces thereof to form an electrical potential thereacross and being water and dissolved CO2 permeable; a ground electrode disposed in electrical contact with the fluid in said measurement chamber; a reference electrode disposed in electrical contact with the fluid in said measurement chamber for providing a stable reference potential independent of ionic activity of the fluid in said reference chamber; and an electrical circuit connected to said first ends of said first and second wires including a first differential signal means connected to said first wire and said ground electrode for generating a first difference signal proportional to the electrical potential difference between said first wire and said ground electrode, a second differential signal means connected to said second wire and said ground electrode for generating a second difference signal proportional to the electrical potential difference between said second wire and said ground electrode, a third differential signal means connected to said reference electrode and said ground electrode for generating a third difference signal proportional to the electrical potential difference between said reference electrode and said ground electrode, a fourth differential signal means connected to said first differential signal means and said third differential signal means for generating a fourth difference signal proportional to the electrical potential difference between said first difference signal and said third difference signal, said fourth difference signal being said pH signal, a fifth differential signal means connected to said second and third differential signal means for generating a fifth difference signal proportional to the electrical potential difference between said second difference signal and said third difference signal, and a sixth differential signal means connected to said fourth differential signal means and said fifth differential signal means for generating a sixth difference signal proportional to the electrical potential difference between said fourth difference signal and said fifth difference signal, said sixth difference signal being said CO2 signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification
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Current AssigneeMallinckrodt Sensor Systems, Inc. (Mallinckrodt plc)
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Original AssigneeDiamond Sensor Systems Incorporated
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InventorsMartin, Glenn, Burgess, Bruce
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Primary Examiner(s)NOT, DEFINED
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Application NumberUS07/126,438Time in Patent Office491 DaysField of Search204/406, 204/409, 204/411, 204/412, 204/415, 204/433US Class Current204/406CPC Class CodesG01N 27/3335 the membrane containing at ...G01N 27/4166 measuring a particular prop...G01N 27/4167 pH electrodes therefor G01N...G01N 33/4915 using flow cells flow cytom...G01N 33/492 Determining multiple analytesG01N 33/4925 measuring blood gas content...
