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FIELD OF THE INVENTION
The invention relates to an electrochemical measuring cell for detecting gas components of a gas sample and includes several measuring or working electrodes and a counter electrode within an electrolyte. A diffusion membrane delimits the access of the gas to the working electrodes.
BACKGROUND OF THE INVENTION
A device for simultaneously detecting different gas components is disclosed in U.S. Pat. No. 5,298,146. This device includes a multiplicity of working electrodes, a common counter electrode and a common reference electrode within an aqueous electrolyte. The working electrodes are mounted segment-like behind a planar diffusion membrane and are subjected to the gas components to be detected via individual orifices which limit the entry of the gas. The orifices are mounted forward of the diffusion membrane. The formation of the measurement value takes place with the aid of a potentiostatic evaluation circuit which selects and controls the potentials at the working electrodes.
It is a disadvantage of this known device that all gas components diffuse through the diffusion membrane and, in this way, can reach all measuring electrodes. This leads especially to incorrect measurements when the entry to the measuring electrode for a gas component must be delimited by a diffusion barrier and/or by a selective filter. The diffusion barrier can, for example, be used when measuring oxygen. A further disadvantage is that the projection surface at the gas side can be utilized only incompletely because insulating intermediate spaces must remain between the electrodes. This is especially the case when trace gases are to be detected. A further disadvantage is that the fixing and insulation of contact leads is complex for a coplanar measuring electrode arrangement.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a measuring cell of the kind described above wherein incorrect measurements because of cross-diffusion are prevented.
The electrochemical measuring cell of the invention is for detecting gas components of a gas sample and includes: a housing having an opening directed toward the gas sample and defining an electrolyte chamber; an electrolyte contained in the chamber; a plurality of measuring electrodes and a counter electrode disposed in the chamber so that the counter electrode is in spaced relationship to the measuring electrodes; a diffusion membrane interposed between the measuring electrodes and the opening for limiting access of the gas sample to the measuring electrodes; and, means for holding a first one of the measuring electrodes in stepped relationship to a second one of the measuring electrodes.
The advantage of the invention is seen in that a cross diffusion of gases to be detected is effectively prevented between individual working electrodes. This advantage is achieved by the arrangement of the measuring or working electrodes on different planes which are mutually parallel and offset relative to each other. Because of the height offset between the working electrodes, the electrode surface of the working electrodes, which is necessary for detecting the components, is optimally utilized. Corresponding gaps between the working electrodes would have to be provided in order to preclude cross-diffusion if the working electrodes would be arranged on a planar surface. In this way, the electrochemically effective surfaces of the working electrodes are however reduced. On the other hand, the diameter of the measuring cell would have to be increased for constant electrode surfaces. This situation can lead to assembly problems. In the electrochemical measuring cell of the invention, the longitudinal extension of the measuring cell is utilized for gap formation, which is generally not subjected to any limitations.
According to a feature of the invention, the diffusion membrane is subdivided into individual membrane segments which are assigned to corresponding working electrodes. The membrane segments together with the working electrodes are mounted so as to be parallel and offset to each other.
In an advantageous manner, an electrode holder has support surfaces which are offset with respect to each other in a step-like manner. The working electrodes with the corresponding membrane segments are attached to corresponding ones of these support surfaces. The electrode holder has a radially extending transverse strut on which the contact leads running to the working electrodes can be attached.
In an advantageous manner, the O.sub.2 working electrode can be configured to have a circular surface. The remaining working electrodes are segments of a circular, annular element which can be arranged concentrically on different planes. These can also be arranged on a common diffusion membrane as long as no disturbing cross diffusion is expected between two working electrodes.
| 10,11-Furo-derivatives of cyproheptadine |
2,4-Dihydroxy-4'-(substituted amino)-diphenylamines |
| 4"-deoxyerythromycin derivatives |
6,6'-diamino-6,6'-dideoxy-1',2,3,3',4,4'-hexa-O-methylsucrose |
| Absorbent polymer modification |
Access cover security device |
| Acoustic apparatus |
Acrylate-containing compositions and their polymerization |
| Active broad-band reception antenna |
Adjustable boyancy fishing float |
| Adjustable dolly |
Adsorbents for polyol purification |
| Air circulator |
Air cooler freeze protection |
| Airbag apparatus for motor vehicles |
Aircraft engine maintenance stand |
| Anamorphic single lens |
Angular position encoder |
| Antenna adapter |
Anti-aggregatory agents for platelets |
| Anti-locking control system |
Antioxidant chroman compounds |
| Apparatus for purifying pollutant gases |
Apparatus for reflow soldering |
| Archery arrow-centering device |
Arrow guide |
| Articulated bed |
Attachment for snow removal |
| Automatic welding machine |
Bag hanger unit |
| Bait container |
Bicyclic amino acids |
| Bone contouring tool |
Borehole pressure gauge |
| Bottle insert for product container |
Broadband telecommunications system |
| Carbanilate compound for erythemal protection |
Card cage shielding contactor |
| Catamaran vessel |
Cementing system |
| Certain N'-alkyl-N'-(2'-alkoxycarbonylbenzenesulfonyl)-N-(2-thiazolyl)glycineami des |
Charged-particle-beam projection-optical system |
| Chemical beneficiation of coal |
Chemical vapor deposition apparatus |
| Cigarette extinguishing storage device |
Cinnamoylpiperidinobutyrophenone antipsychotic agents |
| Citrus juicer |
Climbing device for vehicles |
| Cluster assembly with aligning boss |
Coatings for ink jet nozzles |
| Combination cooler/carrier and umbrella |
Combination outlet strip |
| Common mode bias voltage generator |
Compact projection television system |
| Compositionally modified resistive electrode |
Compressor for use in refrigerator |
| Computer keyboard |
Computer workstation |
| Cooling system for IC package |
Cosmetic device and method |
| Crispy-mix bowl |
Curable resin composition |
| Cyano-enol ethers |
Cycloalkyl derivatives of benzisoselenazolones |
| Dental impression material |
Dental spray handpiece |
| Dicocoamine derivatives of 2,5-dimercapto-1,3,4-thiadiazole |
Digital feedback power supply |
| Dispenser outlet |
Display system |
| Distillate hydrogenation catalyst |
Dive parameter indicating assembly |
| DNA sample collection for identification |
Down the hole drill |
| Downhole seismic array system |
Dressing device |
| Dual circuit lantern |
Durable press/wrinkle-free process |
| Ear pressure equalizer |
Electric axial flow machine |
| Electrically controlled brake actuator |
Electrically operated ratcheting pawl latch |
| Electrolytic stripping bath and process |
Electromechanical earthquake alarm |
| Electronic gain control circuit |
Exercise apparatus for underwater use |
| External skin treatment composition |
Extractor |
| Extrudable fluoropolymer blends |
Fast evacuation device for aircraft |
| Filter jug |
Fishing rig |
| Flat-topped wave-board panel |
Flavin adenine dinucleotide-iodothyronine conjugates |
| Flexible integrated circuit package |
Floodlight |
| Fluid injecting method and apparatus |
Foldable golf cart |
| Foldable stand |
Frame device |
| Freeze-free vent |
Fuel injection control system |
| Genetic method for controlling sprouting |
Glow discharge method and apparatus |
| Gluing machine |
Golf club head |
| Grease composition |
Grid-inserted quantum structure |
| Grinding apparatus |
Gutter assembly |
| Heart pacemaker |
Heat generator |
| Heat resistant copolymer composition |
High speed multiplier |
| Hose coupling |
Illuminating magnifying lens structure |
| Imidate insecticides |
Implant with reinforced resorbable stem |
| Indolizine derivatives, with pharmaceutical activity |
Infant lapmate |
| Injection irrigating process and apparatus |
Insect impeller and destroyer |
| Insecticidally active nitro guanidine compounds |
Integrable differential amplifier |
| Intermediate transfer apparatus |
Interzone mixing device |
| Joint for tubings |
Laser amplifier system |
| Liquid crystal display element |
Low glare infrared light source |
| Low noise wide band amplifier |
Low-level radiation waste management system |
| Magazine system of a stapler |
Magnet generator |
| Manufacture of parabolic antennas |
Medical lead having segmented electrode |
| Memory BIST and repair |
Metal detector with bivariate display |
| Method for assembling shafts |
Method for screening calls |
| Method of composing signatures |
Method of compressing electroencephalographic signals |
| Method of manufacturing semiconductor device |
Method of purifying emissions |
| Method of removing hexafluoropropylene dimers |
Micromachined semiconductor magnetic sensor |
| Miniature magnetic latch relay |
Miniaturized direct current fan |
| Mixer |
Motor velocity control |
| Mouth-held holder |
Multilayer porous fabric |
| Multiple chair workstation |
Multiple texture compositing |
| Multipurpose groundwater sampler |
N Phase digital inverter |
| NC program drawing method |
Nitrogen oxides removal method |
| Non-computer learning aid |
Nuclear magnetic resonance imaging apparatus |
| Organic electrolyte battery |
Outdoor window |
| Oxygenating pacifier |
Packaged optical micro-mechanical device |
| Paint film-protective sheet |
Paper roll filter structure |
| PCM communication system |
Pesticidally active O-ethyl-S-N-propyl-O-2,2,2-trihaloethyl-phosphoro(thiono)thiolates |
| Pharmaceutical preparations |
Phase lock device and method |
| Photographic printer mask mechanism |
Piston ring |
| Plant anchor |
Plasma treating device |
| Plasma uric acid lowering method |
Plate filter for filtering liquids |
| Pole sign construction |
Polyester plasticizers for halogen-containing polymers |
| Polymer conversion process |
Polyphase braid reinforced hose |
| Portable pelvic and leg splint |
Potato-strip cutting deceleration system |
| Preparation of 2',3'-didehydro-3'-deoxythymidine from 5-methyluridine |
Press arrangement and method thereof |
| Pressure regulator |
Process for cleaning sugarbeet pulp |
| Process for thermally stabilizing sterols |
Processing system |
| Production method for micromechanical components |
Programmable depth first-in, first-out memory |
| Protective assembly for hypodermic syringes |
Purification method for alpha interferon |
| Radiation-sensitive mixture |
Rear wheel steering apparatus |
| Reciprocating saw holder |
Refrigerator door display lens |
| Resistance spot welder adaptive control |
Rich fume incinerator |
| Rotary plug valve |
Rotary screen liquid-solid separator |
| Rotary-latch lock |
Rotor tip clearance control devices |
| Safeguard device |
Self-illuminating concave video screen system |
| Semi-automatic crossbow apparatus and method |
Silicone release coating compositions |
| Site-of-use installed venting apparatus |
Snap-lock container |
| Soft-tip performance braided catheter |
Split hub assembly |
| Spring clip apparatus |
Stimulated polariton scattering optical amplifier |
| Substituted 1,3-oxathiolanes with antiviral properties |
Support bed |
| Surgeon's command and control |
Swimming instructional device |
| Swing-type actuator |
Switched capacitor offset suppression |
| Syndiotactic monovinylidene aromatic polymerization process |
Telescope level adjusting means |
| Termination adaptor for PCB |
Test scoring machine |
| Thermal air flow meter |
Thread making device |
| Timing system |
Tissue specific prodrug |
| Transport and storage system |
Treatment of acne utilizing N-methyldiethanolamine |
| Tube lining apparatus |
Turbocharger with rotating electric machine |
| Ultraviolet absorbing, green tinted glass |
Valve lifter |
| Vapor phase nitration catalysts |
Vegetation cutting apparatus |
| Vibration type switches |
Volute compressor |
| Walking support system |
Waterborne coating compositions |
| Wireless local area network apparatus |
Working fluid for Rankine cycle |
| Yarn-threading method and device |
The measuring cell of the invention is especially advantageous for simultaneously detecting oxygen, carbon monoxide and/or hydrogen sulfide.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the drawings wherein:
FIG. 1 is a side elevation view, in longitudinal section, of an electrochemical measuring cell according to the invention; and,
FIG. 2 is a plan view of an electrode holder viewed in the direction of arrow A of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1 shows an electrochemical measuring cell 1 wherein a measuring cell housing 2 encloses an electrolyte space 4 filled with an aqueous electrolyte 3. The measuring cell 1 of the invention functions to simultaneously detect oxygen, carbon monoxide and hydrogen sulfide. An electrode holder 6 is arranged at a first end 5 of the measuring cell housing 2. The electrode holder 6 can preferably be made of polypropylene (PP) or polyethylene (PE). The electrode holder 6 has a first gas channel 7 for the detection of oxygen, a second gas channel 8 for the detection of carbon monoxide and a third gas channel 9 for the detection of hydrogen sulfide. The end of the electrode holder 6 facing toward the electrolyte space 4 is configured to have a first support surface 10 for attaching a first membrane segment 11 having an O.sub.2 working electrode 12. The support surface 10 is located in the region of the first gas channel 7.
In a corresponding manner, a second support surface 13 is provided in the region of the second gas channel 8. The support surface 13 is for a second membrane segment 14 having a CO working electrode 15. A third support surface 16 is provided in the region of the third gas channel 9 and is provided for a third membrane segment 17 having a H.sub.2 S work electrode 18. The gas channels (7, 8, 9) are provided with gas-selective filters (19, 20, 21), respectively. These filters hold back those gases which would lead to erroneous measurements at the corresponding working electrodes. The filters can, for example, be made of active charcoal for adsorption and are commercially available, for example, from Dragerwerk AG of Lubeck, Germany.
The gaseous components reach the corresponding working electrodes (15, 18) via respective orifices (22, 23). A diffusion capillary 24 delimits the entry of O.sub.2 molecules to the O.sub.2 working electrode 12.
A sandwich-like assembly is disposed rearward of the O.sub.2 working electrode 12 and includes an electrolyte-permeable first nonwoven fabric 25, an O.sub.2 protective electrode 26 and a second nonwoven fabric 27 which is likewise permeable to the electrolyte. The first membrane segment 11, the O.sub.2 working electrode 12, the nonwoven fabrics (25, 27) and the O.sub.2 protective electrode 26 are attached in a cup-shaped recess 28 within the electrode holder 6. The base of the recess 28 is the first support surface 10 having the diffusion capillary 24. A second end face 29 of the measuring cell housing 2 is disposed opposite the first end face 5 and is closed by a holder 31 for a counter electrode 30. The gas-selective filters (19, 20, 21) forward of the corresponding working electrodes (12, 15, 18) are covered by a dust filter 32. For conducting the measurement, the electrodes (12, 15, 18, 26, 30) are connected to a potentiostat (not shown) in a manner known per se.
A cross diffusion of oxygen between the O.sub.2 working electrode 12 and the working electrodes (15, 18) is prevented because of the step-like recess 34 between the first support surface 10 and the second and third support surfaces 13 and 16. Cross diffusion between the membrane segments (14, 17) is also not possible because of the segment-like diffusion membrane. An erroneous measurement of oxygen is prevented because of the suppression of the cross diffusion.
FIG. 2 shows a plan view of the electrode holder 6 viewed in the direction of arrow A of FIG. 1 with filter 32 as well as filters (19, 20, 21) removed. The gas channels (8, 9) and the working electrodes (15, 18) are configured in the form of sectors and are separated from each other by a radially-extending transverse strut 33. The transverse strut 33 facilitates attachment of contact leads (not shown) which lead to the electrodes (12, 26) and the membrane segments (14, 17).
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
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