Abstract: A system of measuring pH of a solution having a calibration device to counteract time-drift effect. The calibration device of the system adjusts a compensation voltage to zero a measuring voltage of a first sensor and only respond to time-drift voltage of the first sensor. The calibration device has a differential operation amplifier receiving measuring voltages from the first sensor and a second sensor of the system to eliminate the time-drift voltages of the first and second sensors, thereby achieving calibration of the time-drift effects.

Abstract: An ion-sensitive sensor arrangement includes: a semiconductor chip having a first surface, which has a media-sensitive region and at least one, first, electrical contact surface; and a support having a second surface, which faces the first surface of the semiconductor chip. An opening is provided, which aligns with the sensitive region, and at least one, second, electrical contact surface, which overlaps, or aligns with, the at least one, first, electrical contact surface. Between the support and the semiconductor chip, a preferably elastic, anisotropic conductor is arranged, which produces a conducting connection between the at least one, first, contact surface and the at least one, second, contact surface, and which has a traversing opening, which aligns with the opening, so that the sensitive region of the semiconductor chip can be contacted through the opening by an analyte. The preferably elastic, anisotropic conductor seals the region outside of the opening against contamination with the analyte.

Abstract: An electrochemical sensor is provided that includes a housing having an outer wall, a plurality of longitudinal walls disposed within the outer wall, and a reference chamber housing a reference electrode. The longitudinal walls define a plurality of longitudinal chambers. Ionic communication between the target fluid and the reference electrode passes sequentially through each of longitudinal chambers from a first longitudinal chamber to the reference chamber. In this manner, the sensor provides generally a long, tortuous flow path, or salt bridge, between the target fluid and the reference electrode, resulting in a high resistance factor for the sensor.

Abstract: pH-change sensors and related methods are disclosed. One such sensor may have a first ion-sensitive transistor-operational-transconductance-amplifier (the “first IOTA”) and a second ion-sensitive transistor-operational-transconductance-amplifier (the “second IOTA”). Each IOTA may have an ion-sensitive transistor, a load transistor, and an output. In each IOTA, the drain region of the ion-sensitive transistor may be connected to the drain region of the load transistor. A differential sensor may be connected to the IOTAs, and an output from the differential sensor may indicate a voltage difference between the IOTA outputs. The output from the differential sensor may be used to provide an indication of a change in pH.

Abstract: A system automatically maintains at least one of a pH level and a sanitizing agent level of water in a water feature. The system includes a sensor assembly responsive to at least one of a pH level of the water and a sanitizing agent level of the water. The system further includes a controller which generates control signals in response to signals from the sensor assembly. The system further includes at least one of a first source containing a sanitizing agent material and a second source containing a pH-modifying material. The system further includes a third source comprising a valve assembly and a third container containing a liquid calibrant material. The valve assembly is responsive to at least a portion of the control signals from the controller by selectively allowing the calibrant material to flow from the third container through the sensor assembly to the water feature.

Abstract: A biosensor containing ruthenium, measurement using the same, and the application thereof. The biosensor comprises an extended gate field effect transistor (EGFET) structure, including a metal oxide semiconductor field effect transistor (MOSFET), a sensing unit comprising a substrate, a layer comprising ruthenium on the substrate, and a metal wire connecting the MOSFET and the sensing unit.

Abstract: The present invention is a system for monitoring a patient's breath chemistry comprising a plurality of components, including a self-condensing pH sensor distally mounted on a catheter, a transmitter with hydration sensing circuitry for the pH sensor, and, a processing receiver/data recorder. The specifically designed self-condensing pH sensor located on the distal end of the catheter is designed to be inserted into the patient's airway. Monitoring of a patient's breath pH is accomplished by using the miniaturized self-condensing pH sensor, providing for real-time monitoring of patient airway pH values.

Abstract: This invention provides an extended gate ion-sensitive field effect transistor as a pH sensor for measuring the pH value of a solution under test. This invention also provides a pH sensing system comprising a separable and flexible pH sensor for measuring the pH value of a solution under test, wherein the transistor of the pH sensor can be prevented from direct contact with the solution.

Abstract: A reference pH sensor, the preparation and application thereof. The reference pH sensor is an extended gate field effect transistor (EGFET) structure and comprises a metal oxide semiconductor field effect transistor (MOSFET) on a semiconductor substrate, a sensing unit comprising a substrate, a solid-state conductive sensing layer on the substrate, and a polypyrrole layer on the solid-state conductive sensing layer, and a metal wire connecting the MOSFET and the sensing unit.

Abstract: A urea concentration identification device comprising a concentration identification sensor unit (2) and a support unit (4) attached at the bottom end thereof with this sensor unit and provided at the top end thereof with a mounting unit (4a) to a urea solution tank opening. The concentration identification sensor unit (2) has an indirectly-heated concentration detector and liquid temperature detector provided with metal fins (21c),(22c), respectively, for heat-exchanging with urea solution. The concentration identification sensor unit (2) is provided with a cover member (2d) that forms an opposite-ends-opened urea solution induction passage so as to surround the metal fins (21c), (22c).

Abstract: An electrochemical suspended element-based sensor system includes a solution cell for holding an electrolyte comprising solution including at least one electrochemically reducible or oxidizable species. A working electrode (WE), reference electrode (RE) and a counter electrode (CE) are disposed in the solution. The CE includes an asymmetric suspended element, wherein one side of the suspended element includes a metal or a highly doped semiconductor surface. The suspended element bends when current associated with reduction or oxidation of the electrochemically reducible or oxidizable species at the WE passes through the suspended element. At least one measurement system measures the bending of the suspended element or a parameter which is a function of the bending.

Abstract: A wireless pH measurement system is disclosed, the wireless pH measurement system includes a portable module and a receiver end. The portable module comprises a signal detecting and processing portion and a wireless transmission portion. The signal detecting and processing portion comprises a sensor unit for detecting a pH signal, amplifying, filtering noise, analog/digital conversion and numerical processing to generate a pH measurement signal. The wireless transmission portion receives the pH measurement signal via a transmission interface and transmits by a Bluetooth module. The receiver end includes a Bluetooth receiver for receiving the pH measurement signal. The receiver end processes the pH measurement signal by programs, displays, analyzes and stores the pH measurement signal and transmits warning signal when an abnormal pH measurement signal is received.

Abstract: A potentiometric sensor, especially a pH-sensor or redox-sensor, includes: an elementary sensor for registering a potentiometric parameter, especially a pH-value or a redox potential; and an interface for issuing a potentiometric-parameter-dependent signal to a superordinated unit, especially a transmitter; wherein the potentiometric sensor of the invention has a digital data memory, which is permanently connected with elementary sensor.

Abstract: An electrochemical electrode probe includes an elongated body of a porous material disposed in a housing. The porous material is permeated with an electrolyte. A body of electrode material surrounds the porous body and functions as one electrode of an electrochemical system. A portion of the elongated body of porous material projects beyond the electrode body and functions to establish ionic and electrical conductivity with a sample of material which is to be tested. The sample of material functions as a working electrode, and the electrode body of the probe functions as a counter electrode/reference electrode. Further disclosed is an electrochemical analysis system which includes the probe and a support plate operable to retain a plurality of samples of test material thereupon. The probe is moved across the plate to sequentially measure the electrochemical properties of the various samples of material. Also disclosed are methods for using the system.

Abstract: A process analytic sensor for sensing a characteristic of a process fluid is disclosed. The sensor includes a housing including a sensing portion having an electrical characteristic that varies with a characteristic of the process fluid. An instrument cable has at least one electrical conductor. An electrode connection space is located within the housing and the at least one electrical conductor is electrically coupled to a respective conductor of a sensing element of the sensing portion. A fill material is disposed in the electrode connection space. The fill material cures through exposure to moisture and the fill material is uncured and sealed within the electrode connection space.

Abstract: A insertion electrode device, which is configured for installing a sensor probe in a container for a measuring medium, includes a probe housing that can be attached to the container and has a probe protector tube serving to receive, hold and guide the sensor probe. The sensor probe has a coupling for electrical connections, and the probe housing is equipped with a protective sleeve to protect the coupling from mechanical stress and moisture. The protective sleeve is connectable to the probe protector tube. A safety adapter is coupled to the end of the probe protector tube that is outside the container. The safety adapter engages a recess of the sensor probe or reaches over a step of the sensor probe and thereby secures the latter against moving in the axial direction.

Abstract: A system to detect a presence of a specific gas in a mixture of gaseous byproducts comprising moisture vapor is disclosed. The system includes an electrochemical cell, a transport to deliver the mixture of gaseous byproducts from the electrochemical cell, a gas sensor in fluid communication with the transport, the sensor responsive to a presence of the specific gas to generate a signal corresponding to a concentration of the specific gas, and a membrane to prevent transmission of liquid moisture, the membrane disposed between the transport and the gas sensor.

Abstract: A hydrogen sulfide sensor is made from a metal acetate film, such as a thin film of copper acetate, formed on a set of monitoring electrodes, by evaporation of a metal acetate aqueous solution disposed on the electrodes, for detecting a weak gas, such as hydrogen sulfide, carried in a gas carrier, such as a nitrogen carrier, for detecting low concentration of the weak gas, such as ten ppm, when the conductivity of the film changes by several orders of magnitude, that produces a metal sulfide, such as copper sulfide, that is a good electrical conductor at room temperature, for example, as the metal acetate is converted directly to a metal sulfide upon exposure to hydrogen sulfide.

Abstract: A reference electrode including a water-impermeable, non-conductive substrate having a surface; an electrically conductive metal/metal salt mixture layer in contact with the surface; a water-soluble alkali metal salt layer; and a water-impermeable barrier layer overlaying a portion of the alkali metal salt layer and a portion of the metal/metal salt layer, and a method for preparing same are described. When the reference electrode is placed in a water sample to be tested, water enters the exposed portion of the alkali metal salt layer where it dissolves the salt forming a saturated solution in the region of contact between the alkali metal salt layer and the metal/metal salt layer.

Abstract: A signal processing circuit includes an ion sensitive field effect transistor, a reference electrode for the ion sensitive field effect transistor, a metal oxide semiconductor transistor having its gate coupled to the reference electrode, and a biasing circuit. The biasing circuit is configured to bias the ion sensitive field effect transistor and the metal oxide semiconductor field effect transistor to operate in a weak inversion region and to provide an output current signal.

Abstract: A reference electrode for potentiometric measurements has a housing (2) with a hollow space (4) containing a liquid reference electrolyte (6) as well as a conductor element (8) immersed in the reference electrolyte. In addition, the housing has a diaphragm (12) through which the reference electrolyte can be brought into contact with a measuring medium (10) outside of the housing. Furthermore, means are provided to effect an outflow of the reference electrolyte through the diaphragm. A first electrical contact element (20, 36) is arranged in the hollow space in such a manner that the contact element is immersed in the reference electrolyte as long as the fill level (18) of the reference electrolyte does not fall below a threshold value (FS), and that the contact element is not immersed in the reference electrolyte if the fill level falls short of the threshold value.

Abstract: The present claimed invention is to provide a reference electrode wherein variations of a potential difference at a liquid junction can be removed almost completely, contamination of a sample solution can be minimized, a frequency to supply and replace an internal solution is lessened, the liquid junction is prevented from being clogged, high durability for a long term can be maintained and a measurement with high accuracy can be conducted, and comprises an internal electrode 21, an internal solution 22 that makes a contact with the internal electrode 21 and a liquid junction 23 that continues into the internal solution 22, wherein the liquid junction 23 is made by the use of a gelled hydrophobic ionic liquid.

Abstract: A potentiometric sensor for measuring a potentiometric variable of a medium comprises an ISFET whose gate region exhibits an ion-sensitive surface which can be exposed to the medium and which outputs an output signal that depends on the concentration of the ions at the ion-sensitive surface of the gate region. An evaluation circuit with a measuring input to which the output signal of the ISFET is applied is included, whereby the evaluation circuit is designed to output a measured value for the potentiometric variable, depending on the output signal. Also included is a measuring resistor which is arranged between the output of the ISFET and the input of the evaluation circuit, a monitoring circuit to determine the voltage drop over the measuring resistor, and a bridge section that is parallel to the measuring resistor to bridge the measuring resistor whereby the bridge section exhibits a switch with which the bridge section can be opened or closed.

Abstract: The invention relates to a measuring device having a penetrating electrode. Said elongated electrode of the measuring device is movably mounted in axial direction thereof. In case of a load or a shock, it can absorb said load to a given degree in the housing of said measuring device. Said shock-absorbing characteristic makes it possible to largely prevent breaking of the first electrode that is preferably configured in the form of a glass electrode. The invention also relates to a measuring device, to a method for the production and the application of said measuring device.

Abstract: A pH half-cell method and apparatus includes an electrode, a pH sensitive glass membrane and an electrolyte in electrolytic contact with the electrode and membrane. The membrane includes at least about 15 mole percent lithium, and the electrolyte includes a lithium salt as the predominant monovalent cation. The pH half-cell is used with a reference half-cell and meter to provide an electrochemical potential measurement sensor, optionally with both half-cells disposed within a single housing. The lithium salt electrolyte is also used in a method for storing, conditioning, preserving and/or rehabilitating a pH half-cell.

Abstract: A first aqueous solution filled in an electrolytic cell (2) is electrolyzed by applying DC voltage between the electrodes 7a and 7b in said electrolytic cell 2, to form an oxidation field short of electrons in said aqueous solution; and then, a second aqueous solution with carboxylic acid dissolved in it is mixed into the first aqueous solution in oxidation field state, so that the first aqueous solution in oxidation field state obtains electrons and is deoxidized, and the carboxylic acid is oxidized, to produce carbonic acid gas in said aqueous solution. Therefore, the present invention can be used to produce carbonic acid gas solution at a low cost easily.

Abstract: The present claimed invention intends to provide a responsive glass membrane for ion selective electrode glass and an ion selective electrode comprising the responsive glass membrane that produces a self-cleaning function when the ultraviolet rays are irradiated although no change is brought in a composition of a sample solution as being an object to be measured and that is low in electric resistance value and superior in responsivity under an ordinary measurement environment. The responsive glass membrane for ion selective electrode is made of the titanium-containing oxide glass that contains 20˜80 mol % of titanium dioxide and lithium oxide.

Abstract: The present invention pertains to a means of combining and configuring specific hydrophilic and dielectric materials in such a way as to allow an antimony/reference electrode pH sensor to be packaged and stored dry yet become fully hydrated to an activated state after exposure to aqueous liquids. The sensor is packaged and stored dry to maintain component stability and minimize component degradation. When the user removes the sensor from the package and the sensor tip is submerged in a hydration (ion conduction) media or solution, the hydrophilic coating along with the impregnated reference wick, absorb the fluid to create an electrolytic gel inside the reference wick, which activates the pH sensor.

Abstract: A device for adjustment of the pH of a target liquid includes a working electrode (10), an electrolyte chamber (16) which holds an electrolyte (14), a counter electrode (12) in electrical contact with the electrolyte, a junction (18) which spaces the electrolyte from a target liquid (20) when the working electrode is in contact therewith, and a source of current (22), for supplying current to the working electrode for electrolysis of water at the working electrode, whereby the pH of the target solution is adjusted.

Abstract: A flowing junction reference electrode comprises a microfluidic liquid junction member situated between a pressurized reference electrolyte solution and a sample solution. The liquid junction member has an array of nanochannels spanning the member and physically connecting the electrolyte and the sample. The number of nanochannels in the array can be between 10 and 108. Preferably, the nanochannels are substantially straight and parallel to one another. The nanochannels can be coated to facilitate the flow of the electrolyte solution through the junction member. The nanochannels can have widths of between 1 and 500 nanometers, and the width of any one nanochannel is substantially equal to the width of any other nanochannel. The member can be manufactured out a polymer such as polycarbonate and polyimide, and may also be made of silicon, glass, or ceramic. In one embodiment, the reference electrode includes means for pressurizing the electrolyte solution.

Abstract: A semi-permanent reference electrode for use in monitoring and measuring metals in field applications, such as cathodic protection. This electrode has an outer electrode body with a cap and porous plug. The outer electrode body is filled with a fill solution which is a saturated salt solution formed from a solid salt. The solid salt is hygroscopic with a low deliquescence point. An opening is provided in the cap to allow moisture into the outer electrode body to combine with the fill solution to maintain the saturated salt solution in the field. This saturated salt solution must maintain a constant pH for use in the semi-permanent reference electrode. A wire is used within the outer electrode body which connects to a voltmeter. This voltmeter measures the potential difference between the reference electrode and the field component of interest, which can include pipelines, storage tanks and bridges.

Abstract: Soot sensing systems and soot sensors are provided. In one exemplary embodiment, a soot sensor includes a non-conductive substrate and a first electrode disposed on the non-conductive substrate. The soot sensor further includes a second electrode disposed on the non-conductive substrate and spaced away from the first electrode. The soot sensor further includes a first protective layer disposed over at least a portion of the first electrode. The soot sensor further includes a second protective layer disposed over at least a portion of the second electrode. Further, an electrical parameter between the first and second electrodes is indicative of an amount of soot disposed on the non-conductive substrate between the first and second electrodes.

Abstract: A ruthenium oxide electrode. The ruthenium oxide electrode includes a substrate, a ruthenium oxide film formed thereon, and a conductive wire connecting to the ruthenium oxide film. The invention also provides a method of fabricating the ruthenium oxide electrode.

Abstract: Carbon nanotubes have been reversibly and readily oxidized and reduced with common chemicals in solution, thereby allowing the nanotubes to be used as catalysts for chemical reactions and as stable charge storage devices.

Abstract: A method and system is disclosed for monitoring one or more characteristics associated with a fluid. An insulating layer comprising non-conducting diamond is positioned within a housing and has a surface exposed directly or indirectly to the fluid. A plurality of microelectrodes made of electrically conducting diamond each have a surface exposed directly or indirectly to the fluid. An electrical circuit in electrical communication with each of the microelectrodes is adapted to convert electrical signals from the microelectrodes into at least one signal associated with a characteristic being monitored. The sensing system is well suited to hydrocarbon wellbore related applications, but can also be used in other applications.

Abstract: The invention comprises novel apparatuses and testing methods for evaluating a fluid diffusion component. The apparatus includes a fluid capable of undergoing oxidation or reduction, a half-cell electrode assembly able to receive the fluid, and a change in acidity indicator in communication with the assembly. An inventive method of the invention includes the steps of passing a fluid capable of undergoing oxidation or reduction through a half-cell electrode assembly to form a sample, contacting the sample with an indicator, and detecting a change in acidity in the indicator.

Abstract: The sensor arrangement includes: a least two sample chambers; at least two potentiometric FET-sensors, especially ISFET-sensors or ChemFET-sensors, having, in each case, a sensitive surface section, wherein each sensitive surface section lies in flow connection with its one of the sample chambers; and a reference cell having a reference medium for providing a reference potential, wherein the sample chambers are connected with the reference medium via an electrolyte bridge. The reference cell has, preferably, a potentiometric reference-FET-sensor for providing a reference potential, which is registered against the pseudo-reference-potential of a redox electrode. The potentials Udiff1, Udiff2, . . .

Abstract: A polymer electrolyte for an electrochemical half cell, in particular for a reference half cell, contains a polymer which as a first monomer component contains at least one alkyl methacrylate. The alkyl methacrylate has a substituted alkyl group with from three to seven carbon atoms and at least two substituents. The aforementioned substituents are selected from the group comprising OR1 and NR2R3, in which R1 , R2 and R3 are selected from the group comprising hydrogen, methyl, and ethyl, on the condition that the substituted alkyl group contains the substituent OH at most once.

Abstract: A measuring device having a plurality of potentiometric electrode pairs situated on a substrate is described. One of the electrodes of each electrode pair represents a reference electrode and the other electrode represents a pH-sensitive working electrode. The electrode pairs form an interdigital structure, and the substrate is covered by a mask in such a way that the individual electrode pairs are separated from one another at least in the area of the interdigital structures of the electrode pairs.

Abstract: Disclosed are combination glass pH electrodes, the standard potential of which is stabilized by means one or more of the following structural modifications: (a) incorporating a noble metal internal element in the pH half-cell; (b) incorporating a noble metal internal element in the reference half-cell; (c) incorporating an internal pH bulb electrolyte with stable pH and oxidation-reduction potential; (d) incorporating an homogenous reference electrolyte with stable oxidation-reduction potential and equitransferent salt; (e) incorporating a liquid junction composed of a porous, inert material; (f) incorporating a reference electrolyte compartment vent; (g) incorporating a storage sleeve, with or without an absorbent medium located therein.

Abstract: An object of the present invention is to suppress an electric potential drift as described above and improve pH measurement precision in order to obtain practical measurement precision in the dry-type multilayered film-type pH electrode. The present invention provides a complex pH electrode which has at least two ion-selective electrodes comprising a non-conductive support, a pair of electrode layers, an electrolytic layer and an ion-selective membrane where at least one of the ion-selective electrode is a hydrogen ion-selective electrode, wherein the hydrogen ion-selective membrane is saturated with carbon dioxide gas.

Abstract: The present invention pertains to an apparatus and a means of constructing a pH sensor that can detect changes in pH levels of humidified gases and liquid samples. When electronically connected to a computerized or analog display means, sensitive quantitative measurements can be obtained. Given the construction of current pH devices available today, there is a need in the field for a novel, miniaturized, self-condensing pH probe that can be used in fluid or humidified gases.

Abstract: A microfluidic device which electrochemically regulates a pH of a fluid, and a method of regulating a pH of a fluid using the microfluidic device, include a chamber which includes a cathode formed of a metal adsorbing hydrogen gas, and an anode formed of a metal having a higher standard oxidation potential than, and does not react with, water.

Abstract: A measuring device for process technology, useful in measuring- and/or cleaning- and/or calibration-installations in the field of process automation for measuring pH-values and/or redox potentials and/or other process parameters, and an operating method therefor. The measuring device includes at least one central unit having at least one central computer, wherein, in the central computer a management system is provided for the dynamic management of input components (I) and/or output components (O) and/or functional components (F) and/or service components (D) and/or management components (V) and/or interface components (IX) and/or other system components.

Abstract: The present invention pertains to an apparatus for evaluating the signal strength from the pH sensor to determine whether the sensor is hydrated sufficiently to accurately measure pH. This is accomplished by utilizing circuitry that periodically sends a low voltage signal to a suitable pH sensor and then receiving the resulting waveforms which are analyzed by a processing receiver. The electrical connection between a suitable pH sensor and hydration monitoring circuitry is generally hard wired. In one embodiment, a processing receiver is coupled with the hydration monitoring circuitry as a single apparatus. In a second embodiment, the processing receiver can be independent and located remote from the hydration monitoring circuitry. In this embodiment, the hydration monitoring circuitry and the processing receiver are electrically connected using either hard wired techniques or wireless technology. In addition, the processing receiver can include data recording capability.

Abstract: For simplified supply of potentiometric sensors with a reference electrolyte, a sensor plug head for connecting to a cable connection piece of a potentiometric sensor is provided. The sensor plug head including, besides the usual electric connections, a supply connection for connecting to a reference container of the potentiometric sensor. The supply connection includes, preferably, an electrolyte line and the reference container an opening, with the electrolyte line being connectable to the opening, in order to supply the reference container with electrolyte.

Abstract: A sensory apparatus including a substrate including a plurality of sensors to obtain an analyte profile, the sensors including an ion-selective sensor capable of measuring ion content and a chlorine sensor capable of measuring chlorine content, is disclosed. A method of generating an analyte profile, including measuring, directly or indirectly, properties including free chlorine concentration, pH, calcium ion concentration, carbonate ion concentration, and bicarbonate ion concentration, concurrently on a contiguous sample, is also disclosed.

Abstract: A system for monitoring a pH level of a sample medium is disclosed herein as including a pH probe having a pH-sensitive electrode, a reference electrode and a temperature electrode arranged within a housing of the pH probe. The probe housing generally includes a flexible inner tube and a flexible outer tube, the inner tube being concentrically arranged within the outer tube. Preferably, a size of the probe housing minimizes the amount of trauma introduced by insertion of the pH probe into physiological tissues, muscles or fluids. The system also includes a processing means, which is coupled to the pH probe for determining the pH of the sample medium. A method of forming a pH-sensitive electrode, a method of manufacturing a pH probe, and a method for using a pH probe are also disclosed herein.

Abstract: Disclosed is an electrochemical sensor comprising a work electrode and a reference electrode, said sensor adapted to measure the characteristics of a liquid under test, based on the relative electric potential difference and electric current between the work electrode and the reference electrode both immersed in the liquid under test, said work electrode comprising a substrate that reacts to the liquid under test for generating an electric potential according to the concentration of the liquid under test, and said reference electrode comprising a substrate that reacts to the liquid under test for generating a fixed electric potential. According to the present invention, at least one of the work electrode and the reference electrode comprises said substrate coated with a function film for serving to generate the electric potential through the intervention of the film between said substrate and the liquid under test.

Abstract: Disclosed is an electrochemical sensor for measuring carbon monoxide in a gas sample, the sensor comprising a working electrode including a working electrode catalyst, and a diffusion restriction means for restricting the diffusion of the gas sample to the working electrode; wherein the working electrode catalyst comprises oxidised platinum having a hydrogen cross-sensitivity of less than 10% and being present in an amount such that the activity capacity is at least 5.