Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1989-02-23
1990-05-15
Niebling, John F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204414, 204415, 204422, 204431, 429 30, 429 33, 429104, 429192, 324439, 128635, G01N 2726
Patent
active
049255444
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to electrochemical sensing devices utilizing membranes to separate the electrolyte needed by the device from the medium containing the analyte of interest. More specifically, it relates to: (1) gas sensing devices wherein the membrane is utilized to separate the electrolyte from a liquid containing the gas being analyzed, (2) gas sensing devices wherein the membrane is utilized to separate the electrolyte from a gas phase, and (3) ion sensing devices wherein a selectively permeable membrane separates the liquid electrolyte utilized by the device from the analysis solution, which contains an analyte able to diffuse freely through the membrane.
Included in gas sensing devices wherein the membrane is utilized to separate the electrolyte from a liquid containing the gas being analyzed are the sensors utilized for transcutaneous blood gas monitoring, for clinical laboratory analysis of blood gases, and for laboratory and field measurement of gases such as ammonia, carbon dioxide, oxygen and chlorine. Also included in this category are intravascular (catheter) electrodes with proximal or remote reference electrodes for measuring oxygen or carbon dioxide.
Gas sensing devices wherein the membrane is utilized to separate the electrolyte from a gas phase include electrochemical sensor utilized for measuring gases such as oxygen, carbon dioxide, chlorine, or ammonia in flowing gas streams. Such devices are currently utilized for verifying the oxygen content of gas mixtures used for respiratory therapy.
Ion sensing devices wherein a selectively permeable membrane separates the liquid electrolyte utilized by the device from the analysis solution which contains an analyte able to diffuse freely through the membrane, include, specifically, intravascular electrodes for measuring blood pH, sodium, potassium and glucose.
The invention consists of a method and apparatus to simplify the process of changing the membrane and the electrolyte needed by the electrochemical sensing device. While it is believed that the major value will be with gas sensing devices, the invention can be used with any of the electrochemical devices described above which use replaceable membranes.
Basic to the operation of electrochemical sensors is the presence of an electrolyte, an ionically conducting medium, contacting both the anode and the cathode. In voltammetric oxygen sensors of the Clark type or potentiometric carbon dioxide sensors of the Stow-Severinghaus type or other gas sensors of the types disclosed by Ross and Riseman, this electrolyte is an aqueous solution, sometimes modified by other water-compatible solvents such as ethylene glycol or propylene glycol or glycerol. At times, these other solvents may make up the bulk of the electrolyte solution and the water content may vary from traces to only a few percent.
The membrane in these devices may serve several functions. It can be utilized to prevent evaporation of the electrolyte solvent or to prevent fouling of the electrodes. It can prevent contamination of the electrolyte solution or changes in the solution concentration. It can be selectively permeable, allowing only gases to enter for analysis, or it may allow ions and not proteins to reach the sensing electrodes. It can be a diffusion barrier and provide most of the concentration gradient between the medium being analyzed and the electrode where the analyte is being consumed. It can control the thickness of the electrolyte layer and, under some conditions, control the sensitivity of microelectrodes.
The output stability, i.e., the ability to maintain a reproducible output signal for periods ranging from hours to days when the sensor is exposed to a reproducible gas composition, in both voltammetric and potentiometric sensors, is dependent upon the maintenance of a constant composition in this electrolyte, although the reason for this is different in the two types of sensors.
In voltammetric sensors, e.g., oxygen, stability is dependent upon maintaining the constancy of the diffus
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Gorgos Kathryn
Mandelbaum Howard F.
National Research Development Corporation
Niebling John F.
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