GB2065309A - Determining quantity of mixture constituents - Google Patents

Determining quantity of mixture constituents Download PDF

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Publication number
GB2065309A
GB2065309A GB8037078A GB8037078A GB2065309A GB 2065309 A GB2065309 A GB 2065309A GB 8037078 A GB8037078 A GB 8037078A GB 8037078 A GB8037078 A GB 8037078A GB 2065309 A GB2065309 A GB 2065309A
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United Kingdom
Prior art keywords
electrode
measuring
measuring electrode
mixture
voltage
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GB8037078A
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GB2065309B (en
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Draegerwerk AG and Co KGaA
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Draegerwerk AG and Co KGaA
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Publication of GB2065309A publication Critical patent/GB2065309A/en
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Publication of GB2065309B publication Critical patent/GB2065309B/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
    • G01N27/4045—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors for gases other than oxygen

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

A method and an apparatus for determining the quantity of a constituent in a mixture, preferably a gaseous mixture are provided. The method is carried out with the mixture in an electrochemical cell which has a measuring electrode (2), a reference electrode (3) and a counter electrode (4). A predetermined direct voltage with an alternating component is applied to the measuring electrode relative to the reference electrode and the D.C. current at the measuring electrode is measured to determine the quantity of the constituent in the mixture. The apparatus includes an electrochemical cell having the foregoing electrodes, the measuring electrode including a catalyst in a plastics material on its surface and acting as a gas diffusion electrode, an alternating voltage source and means 6 for measuring the D.C. current at the measuring electrode. <IMAGE>

Description

SPECIFICATION Method and apparatus for determining the quantity of one constituent in a mixture This invention relates to a method and an apparatus for determining the quantity of an constituent in a mixture, and more particularly is concerned with such a method when carried out in an electrochemical cell having a measuring electrode, a counter electrode and a reference electrode. A known voltage is applied to the measuring electrode relative to the reference electrode and the current at the measuring electrode is measured to determine the quantity of the constituent in the mixture.
The present invention is more particularly, but not exclusively, concerned with determining the quantity of a gaseous impurity in a gas mixture.
A measuring apparatus of the aforementioned kind, by which different gas mixture constituents such as CO, CH,, etc., can be determined from the current value of the measuring electrode in a redox system with the measuring electrode at an appropriate constant bias voltage, has been described in German Auslegeschrift 21 55 935.
Since a constant voltage is maintained between the gas diffusion electrode (measuring electrode) and the reference electrode with the aid of a voltage regulator, there occur at the measuring electrode owing to the migration of ions between the electrodes which is produced in the measuring operation and owing to the chemical reactions at these electrodes in prolonged use, ageing phenomena which result in a lowering of the sensitivity of the measuring device. Such variations impair the accuracy of the measurement.
According to the present invention there is provided a method of determining the quantity of a constituent in a mixture, wherein the method is carried out with the mixture in an electrochemical cell which has a measuring electrode, a reference electrode and a counter electrode, and the method comprises applying a predetermined voltage to the measuring electrode relative to the reference electrode, the voltage being an alternating voltage, and measuring the D.C. current at the measuring electrode to determine the quantity of said constituent in the mixture.
The mixture can comprise a gas mixture and the said constituent can comprise a gaseous impurity.
Preferably the voltage applied to the measuring electrode is such as to oxidise said constituent.
The voltage preferably alternates between 0.7 V and 1.2 V relative to a hydrogen electrode in a similar mixture. The alternating voltage may have a frequency in the range from 1 KHz to 1 GHz, and it can have a pulse-shaped waveform, with the amplitudes of the pulses varying between the aforementioned voltages. The frequency is advantageously varied in dependence upon the surface of the measuring electrode, its coating and the catalyst, and the mixture constituent to be traced.
By applying an alternating voltage to the measuring electrode, the unwanted ageing effects may be substantially suppressed or made ineffective by regeneration processes.
The present invention also provides an apparatus, for carrying out the above-mentioned method, the apparatus incorporating an electrochemical cell which comprises: a measuring electrode which includes a catalyst in a plastics material on its surface and which, in use, acts as a gas diffusion electrode; a counter electrode; a reference electrode; a voltage source for applying a predetermined voltage to the measuring electrode; and means for measuring the D.C. current at the measuring electrode.
Preferably the catalyst is incorporated in a plastics material having a melting point in the range from 800C to 1800 C, for example polypropylene or polyethylene. Such a plastics material enables the catalyst to be simply bound to the measuring electrode, and during alternating voltage operation may provide favourable ageresisting properties.
For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawing which shows a circuit diagram of an apparatus according to the present invention.
A measuring cell 1 incorporates a plasticscoated gas diffusion electrode 2 (measuring electrode), a reference electrode 3 and a counter electrode 4. A voltage source 5 is connected to the measuring electrode 2 and to an amplifier 7.
The voltage source 5 is also connected via a resistor 8 and a variable resistor 9 to the amplifier 7. The reference electrode 3 is connected to another input of the amplifier 7. An output of the amplifier 7 is connected via a milliammeter 6 and a capacitor 8 in parallel to the counter electrode 4.
The voltage source 5 applies a voltage to the measuring electrode 2 relative to the reference electrode 3. This voltage comprises a D.C.
component of 0.9 volts and a superimposed alternating component of 0.2 volts.
The current value, from which the quantity of a particular constituent of the gas mixture can be determined, is measured by a milliammeter 6. The potential of the reference electrode 3 in relation to the measuring electrode 2 is fixed by the interposition of the amplifier 7. The amplifier 7 maintains a constant mean value of the reference potential between the measuring electrode 2 and the reference electrode 3.
The capacitor 8 bridging the milliammeter 6 ensures that the milliammeter 6 only measures the D.C. component of the current. The value of the capacitor 8 depends upon the chosen operating frequency and may be between 1 ssF and 10 pF.
The gas diffusion electrode 2 comprises a pure silver plate having a polypropylene coating of 1 mm. Powdered platinum is incorporated as a catalyst in the plastics of low melting point i.e. in the polypropylene. The reference electrode 3 and the counter-electrode 4 are formed from noble metal(s).

Claims (13)

1. A method of determining the quantity of a constituent in a mixture, wherein the method is carried out with the mixture in an electrochemical cell which has a measuring electrode, a reference electrode and a counter electrode, and the method comprises applying a predetermined voltage to the measuring electrode relative to the reference electrode, the voltage being an alternating voltage, and measuring the D.C. current at the measuring electrode to determine the quantity of said constituent in the mixture.
2. A method as claimed in claim 1, wherein the mixture comprises a gas mixture and said constituent is a gaseous impurity.
3. A method as claimed in claim 1 or 2, wherein the voltage applied to the measuring electrode is such as to oxidise said constituent.
4. A method as claimed in claim 1, 2 or 3, wherein the voltage applied to the measuring electrode alternates between 0.7 V and 1.2 V relative to a hydrogen electrode in a similar mixture.
5. A method as claimed in any preceding claim, wherein the alternating voltage has a frequency between 1 KHz and 1 GHz.
6. A method as claimed in any preceding claim, in which the alternating voltage has a pulseshaped waveform.
7. A method substantially as hereinbefore described with reference to the accompanying drawing.
8. An apparatus, for carrying out the method as claimed in any preceding claim, the apparatus incorporating an electrochemical cell which comprises: a measuring electrode which includes a catalyst in a plastics material on its surface and which, in use, acts as a gas diffusion electrode; a counter electrode; a reference electrode; a voltage source for applying a predetermined voltage to the measuring electrode; and means for measuring the D.C. current at the measuring electrode.
9. An apparatus as claimed in claim 8, wherein the catalyst is incorporated in a plastics material having a melting point in the range from 80 to 1800C.
10. An apparatus as claimed in claim 8 or 9, wherein the voltage source is connected to the measuring electrode and to one input of an amplifier, the reference electrode is connected to another input of the amplifier, and an output of the amplifier is connected via a milliammeter and a capacitor in parallel, which provide the means for measuring the D.C. current at the measuring electrode, to the counter electrode.
1 An apparatus as claimed in claim 10, wherein the voltage source is connected by a resistor and a variable resistor to the one input of the amplifier and includes two further connections to the amplifier.
12. An apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.
New claims or amendments to claims filed on 2-3-81 Superseded claims NONE New or amended claims
13. An apparatus, for carrying out the method as claimed in any one of claims 1 to 7, the apparatus incorporating an electrochemical cell which comprises: a measuring electrode which includes a catalyst in a plastics material on its surface and which, in use, acts as a gas diffusion electrode; a counter electrode; a reference electrode; a voltage source for applying a predetermined alternating voltage to the measuring electrode; and means for measuring the D.C. current at the measuring electrode.
GB8037078A 1979-12-12 1980-11-19 Determining quantity of mixture constituents Expired GB2065309B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19792949871 DE2949871A1 (en) 1979-12-12 1979-12-12 DEVICE FOR ANALYZING GAS MIXTURES WITH OXIDIZABLE MIXTURES

Publications (2)

Publication Number Publication Date
GB2065309A true GB2065309A (en) 1981-06-24
GB2065309B GB2065309B (en) 1984-02-29

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GB8037078A Expired GB2065309B (en) 1979-12-12 1980-11-19 Determining quantity of mixture constituents

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DE (1) DE2949871A1 (en)
GB (1) GB2065309B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1990012315A1 (en) * 1989-04-04 1990-10-18 Neotronics Limited Fault detection in electrochemical gas sensing equipment

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4302315A (en) * 1980-06-18 1981-11-24 Becton, Dickinson And Company Gas sensing unit
DE4225775C2 (en) * 1992-08-04 2002-09-19 Heraeus Electro Nite Int Arrangement for continuously monitoring the concentration of NO in gas mixtures

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3644824A (en) * 1970-02-09 1972-02-22 Atomic Energy Authority Uk Polarograph apparatus
DE2530834C2 (en) * 1975-07-10 1985-06-13 Albert Prof. Dr. 3550 Marburg Huch Device for percutaneous measurement of perfusion efficiency

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1990012315A1 (en) * 1989-04-04 1990-10-18 Neotronics Limited Fault detection in electrochemical gas sensing equipment
US5202637A (en) * 1989-04-04 1993-04-13 Neotronics Limited Fault detection in electrochemical gas sensing equipment

Also Published As

Publication number Publication date
GB2065309B (en) 1984-02-29
DE2949871A1 (en) 1981-06-25

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