Abstract: In solid-state chemical sensors, such as the highly sensitive and selective sensor for the detection of halogenated compounds comprises a bead of sodium lanthanum fluoride silicate, having the molecular formula NaLa.sub.4 (SiO.sub.4).sub.3 F, the performance and lifetime are adversely affected by a build-up of insulating reaction product between two electrodes. To prolong the lifetime, intermittent sensor operation is achieved by applying a voltage between the sensor electrodes during only a small fraction of each measurement cycle and/or by reversing the voltage in successive measurement intervals and/or by switching the connections between additional reserve electrodes and/or by periodically exposing the sensor to chemically filtered air at regular time intervals during a major fraction of each measurement cycle. The response speed and sensitivity of the NaLa.sub.4 (SiO.sub.4).sub.

Abstract: A relatively inexpensive modular component that can be substituted for, or used in conjunction with, an existing smoke detector in a commercially available residential fire-detection alarm comprises: (A) an amperometric sensor for carbon monoxide, in which the reference and counter electrodes are combined either internally into a single auxiliary electrode or externally by electrical shorting; and (b) a simple current-to-voltage converter circuit that converts the current signals from the sensing electrode into amplified voltage signals. The converter circuit is powered by the same battery (usually a 9-volt dry cell) and is connected to the same alarm-triggering circuit that are used in existing residential fire alarms. The sensor-and-converter module is designed to fit into a commercially available smoke-detector-type fire alarm unit. The electrical output of the module is designed to be compatible with the electrical input requirements of the commercial detection circuitry.

Abstract: An optical waveguide sensor for the detection of acid vapors comprises a chemically sensitive reagent coating of bromothymol blue or thymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562-nm light-emitting diode source and a phototransistor detector. The response to HCl and H.sub.2 S vapors is both rapid and reversible, with an estimated detection limit for H.sub.2 S of less than 15 ppmv (parts per million by volume). The sensor exhibits generalized response to protonic acid vapors, but does not produce an indicator response to CO.sub.2, even at large concentrations (60 volume-%) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a differential approach, either using a reference sensor (Nafion without an indicator) or by monitoring the sensor responses at two wavelengths.

Abstract: A highly sensitive and selective sensor for the detection of halogenated compounds comprises a bead of sodium lanthanum fluoride silicate, having the molecular formula NaLa.sub.4 (SiO.sub.4).sub.3 F, in which are embedded two noble metal electrodes, preferably a straight platinum wire near the center and a helical platinum wire near the periphery of the bead. A current passing through the helical wire maintains the sensor temperature at about 550.degree. C. by resistive heating. The electrical resistance between the two wires is deduced from measurements of the current passing through a fixed external resistor when a substantially constant voltage, preferably about 4 volts, is applied between the wires. A decrease in the measured resistance is an indication of the presence of a halogenated compound in the sample of air to which the bead is exposed. The sensor is preferably controlled by a microprocessor or microcomputer that also performs data processing.

Abstract: A potentiostat for an amperometric sensor uses a voltage-controlled current source (VCCS), which may be either unidirectional or, preferably, bidirectional. An error amplifier compares the potential of the sensor's reference or counter electrode, relative to ground potential, to a set-point potential. The error voltage serves as an input to the VCCS. The output of the VCCS--a current proportional to the error voltage--is supplied to the sensor's auxiliary electrode. In a steady state, the error voltage is just large enough to supply current that is equal to the current through the sensor's working and auxiliary (or counter) electrodes. The error voltage can either serve directly as an output voltage or it can be amplified without introducing a feed-back loop disturbance. The VCCS permits direct grounding of the sensor's working electrode and operation of the error amplifier at a low or moderate gain, so as to increase the circuit's frequency response and reduce the probability of oscillation.

Abstract: A method capable of detecting low concentrations of a pollutant or other component in air or other gas, utilizing a combination of a heating filament having a catalytic surface of a noble metal for exposure to the gas and producing a derivative chemical product from the component, and an electrochemical sensor responsive to the derivative chemical product for providing a signal indicative of the product. At concentrations in the order of about 1-100 ppm of tetrachloroethylene, neither the heating filament nor the electrochemical sensor is individually capable of sensing the pollutant. In the combination, the heating filament converts the benzyl chloride to one or more derivative chemical products which may be detected by the electrochemical sensor.

Abstract: Selective detection of an analyte in a gaseous mixture is achieved by a chemical, especially amperometric, sensor, that is responsive to the analyte, and a pump-and-valve system, controlled by programmed electronic circuitry, which causes: a) ambient air to pass first through a chemical filter, that removes those air constituents to which the sensor may be responsive, and next through a sorbent-containing tube and the sensor; b) a portion of the gaseous mixture to be first drawn into a sample port and next flushed from the port into the sorbent tube; c) analyte-containing eluent from the sorbent tube to reach the sensor; and d) another mixture component to which the sensor may be responsive to be prevented from reaching the sensor. The sorbent-containing tube has a different retentivity for the analyte than for the other mixture component. The air flow rates and paths can be programmed and the volume of the mixture portion may be auto-ranged to maximize the accuracy of the sensor signals.

Abstract: A portable instrument for use in the field in detecting, identifying, and quantifying a component of a sampled fluid includes a sensor which chemically reacts with the component of interest or a derivative thereof, an electrical heating filament for heating the sample before it is applied to the sensor, and modulator for continuously varying the temperature of the filament (and hence the reaction rate) between two values sufficient to produce the chemical reaction. In response to this thermal modulation, the sensor produces a modulated output signal, the modulation of which is a function of the activation energy of the chemical reaction, which activation energy is specific to the particular component of interest and its concentration. Microprocessor which compares the modulated output signal with standard responses for a plurality of components to identify and quantify the particular component of interest.

Abstract: The BTU content of a sample of natural gas is measured using a computer controlled microcalorimeter micro-sensor instrument employing a catalytic sensor. The instrument is portable for in field use and is able to obtain measurement accuracy of better than .+-.1%. A carrier gas, a standard reference gas and the sample gas to be measured are injected in a controlled manner through use of computer controlled solenoid valves and flow control valves, and a measurement loop injects precise gas volumes to enable a highly accurate BTU measurement by the catalytic sensor.

Abstract: A portable system for analyzing a fluid sample includes a small, portable, low-pressure and low-power chromatographic analyzer and a chemical parameter spectrometry monitor including an array of sensors for detecting, identifying and measuring the concentrations of a variety of components in the eluent from the chromatographic analyzer. The monitor includes one or more operating condition controllers which may be used to change one or more of the operating conditions during exposure of the sensors to the eluent from the chromatography analyzer to form a response pattern which is then compared with a library of previously established patterns. Gas and liquid chromatographic embodiments are disclosed. In the gas embodiment, the operating condition controllers include heated filaments which may convert electrochemically inactive components to electrochemically active products. In the liquid chromatography embodiment, low-power, liquid-phase equivalents of heated filaments are used with appropriate sensors.

Abstract: A sensor includes a vapor sensitive medium and a means for monitoring at least one property of the vapor sensitive medium. The vapor sensitive medium is chosen such that it exhibits a response to the vapors absorbed by an absorbent bed which is substantially the same as the response of the absorbent to the vapors absorbed. The monitored property is a function of the response of the vapor sensitive medium to the vapors absorbed. Also disclosed are an absorbent bed alarm system employing the sensor and a filter cartridge which employs the adsorbent bed alarm system.

Abstract: A portable instrument for use in the field in detecting, identifying, quantifying, and monitoring gas, liquid or solid materials is disclosed. The instrument may analyze either liquids or gases depending upon the type of sensor array therein. The instrument also includes means for changing a gas, liquid or solid to a fluid material. The instrument further includes an array or small sensors which, upon exposure to the unknown material, form a pattern of electrical responses, a source of previously formed response patterns characteristic of various materials, and microprocessor means for comparing the sensor-formed response pattern with one or more previously-formed response patterns to thereby identify the material on a display. The number of responses may be increased by changing the operating voltage, temperature or other condition associated with one or more sensors to provide a plurality of responses from each of one or more of the sensors.

Abstract: Methods for spin coating electrolytic materials onto substrates are disclosed. More particularly, methods for depositing solid coatings of ion-conducting material onto planar substrates and onto electrodes are disclosed. These spin coating methods are employed to fabricate electrochemical sensors for use in measuring, detecting and quantifying gases and liquids.

Abstract: A portable instrument for use in the field in detecting and identifying a hazardous component in air or other gas including an array of small sensors which upon exposure to the gas from a pattern of electrical responses, a source of standard response patterns characteristic of various components, and microprocessor means for comparing the sensor-formed response pattern with one or more standard patterns to thereby identify the component on a display. The number of responses may be increased beyond the number of sensors by changing the operating voltage, temperature or other condition associated with one or more sensors to provide a plurality of responses from each of one or more of the sensors. In one embodiment, the instrument is capable of identifying anyone of over 50-100 hazardous components.

Abstract: A method and instrument including an electrochemical cell for the detection and measurement of methane in a gas by the oxidation of methane electrochemically at a working electrode in a nonaqueous electrolyte at a voltage about about 1.4 volts versus R.H.E. (the reversible hydrogen electrode potential in the same electrolyte), and the measurement of the electrical signal resulting from the electrochemical oxidation.

Abstract: Methods and apparatus are provided for sensing gases in the environment wherein electrochemical sensing procedures are utilized not only for monitoring ambient continuously for the presence of such gases; but also, for the periodic automatic recalibration and self-adjustment of the sensing instrument, as required, to accommodate changing conditions with time. Such accommodation includes not only changes in the instrument itself, but also changes in the environment affecting the accuracy of the monitoring function. The instrument is connected with a microprocessor, or other information storage or retrieval instrumentation which controls the periodic recalibration by measuring, separately from the monitoring function, the electrochemical response to a sample of the gas being monitored, and by adjusting the subsequent instrument readings to reflect the recalibration. During this recalibration procedure, the instrument can be adjusted to zero reading for accommodating drift, as will be understood.

Abstract: A wick system for an electrochemical cell is provided to assure the connection between the electrodes of the cell. The wick system of the invention absorbs electrolyte and by capillary action provides a continuous electrolyte path between the electrodes. The wick may be in the form of a substantially flat piece extending in one plane for those cells having all electrodes positioned at one end thereof. Alternatively, the wick may be substantially tubular to extend from one end of a cylindrical electrolyte containing chamber to another, for a cell having electrodes positioned at each end thereof. Additionally, the wick may extend from one end of the cell to the other in a folded bellows-like form. In any of the forms, the wick system allows for a continuous operation of the cell, even with reduced electrolyte content, and regardless of the three-dimensional orientation of the cell, by absorbing electrolyte and maintaining electrolytic contact.

Abstract: An electrochemical sensing device comprising a sensing electrode, a counter electrode, an electrolyte in contact with said sensing electrode and counter electrode, said sensing electrode comprising a porous hydrophobic substrate having vapor-deposited thereon a porous film of a catalyst to provicde a diffusion electrode, means for exposing said sensing electrode to the gas to be detected, means electrically coupled to said sensing electrode for maintaining said sensing electrode at a potential of about 0.4 volt to about 1.5 volt with respect to the potential of the reversible hydrogen couple in the electrolyte of said cell, and means for measuring current flowing between said sensing electrode and said counter electrode which measured current is a measure of the concentration of the noxious gas being detected.

Abstract: Methods and apparatus are provided for sensing reducible gases in the environment. The invention herein utilizes electrochemical sensing procedures incorporating gold as the sensing electrode in combination with a material selected from the group of iridium and ruthenium as the counterelectrode. This combination avoids the usual polarization at the anode in prior arrangements of this kind and the gradual degradation in the degree of sensing specificity for sensing, for example, NO.sub.2 and Cl.sub.2. In those instances wherein a three electrode system is used, the third or reference electrode may be comprised of platinum, iridium or ruthenium.

Abstract: Hydrazine vapors are electrochemically detected and measured by an apparatus comprising in combination intake means, an electrochemical cell, means for drawing said gas through said intake means and into said electrochemical cell, communicating means communicating said intake means with said cell, at least the internal surfaces of said intake means, said communicating means and said cell being of an inert material, the electrochemical cell comprising a sensing electrode, a counterelectrode, a reference electrode at which substantially no current flows, and an aqueous alkaline electrolyte in contact with said sensing electrode comprising a noble metal catalyst bonded to a hydrophobic material to provide a diffusion electrode, means for exposing said sensing electrode to said gas, means electrically coupled to said sensing electrode for maintaining said sensing electrode at a fixed potential of about 0.7 volt to about 1.