Electrical measuring cell for determinging ammonia, amines, hydrazine amines, hydrazine and hydrazine derivatives

• US 5,344,546 A
• Filed: 02/19/1993
• Issued: 09/06/1994
• Est. Priority Date: 04/29/1989
• Status: Expired due to Term

• Current Assignee: Dragerwerk AG
• Original Assignee: Dragerwerk AG
• Inventors: Kiesele, Herbert, Kuhn, Uwe, Haupt, Stephan
• Primary Examiner(s): Tung, T.
• Application Number:
  US08/019,764
• Time in Patent Office: 564 Days
• Field of Search: 204/153.14, 204/153.17, 204/412, 204/415, 204/431, 204/432
• US Class Current: 204/415
• CPC Class Codes: G01N 27/4045 for gases other than oxygen
• CPC Class Codes: G01N 33/0054 for ammonia
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

The invention is directed to an electrochemical cell for measuring ammonia, amines, hydrazine and hydrazine derivatives and includes a measuring electrode in an electrolyte. The measuring electrode is provided with a coating made of a transition metal oxide and is improved in that its measuring sensitivity during long-term loading is increased. The cross sensitivity of the measuring cell is reduced especially with respect to NO₂ and SO₂. For this purpose, the oxide constituents of the coating are made of a metal conducting oxide of one element or an oxide mixture of several elements of the platinum metal group. Oxides of ruthenium and iridium have proven especially useful. The invention is also directed to an electrochemical measuring cell for measuring ammonia or hydrazine and includes at least a measuring electrode and a counter electrode in an electrolyte. The measuring cell provides a signal increase having a shorter response time and an improved signal stability. For this purpose, the electrolyte is an aqueous solution of a hygroscopic salt of an alkali metal or alkaline earth metal such as calcium nitrate or lithium nitrate or a mixture of both salts.

Claims

1. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the ambient, the measuring cell comprising:

a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;

a soluble electrolyte contained in said chamber;

a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;

a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other;

said soluble electrolyte being an aqueous solution of a hygroscopic salt of an alkali metal and an ammonium salt;

said hygroscopic salt having a concentration in said aqueous solution for preventing solidification of said solution down to a temperature in the range of -10°

C. to -50°

C.; and

,

said ammonium salt having a concentration of 10^-3 to 10^-1 M.

2. The electrochemical measuring cell of claim 1, wherein said hygroscopic salt has a cationic component and an anionic component;

said cationic component being lithium; and

, said anionic component being selected from the group consisting of a nitrate, bromide and chloride; and

, said ammonium salt being selected from the group consisting of ammonium nitrate and ammonium chloride.

3. The electrochemical measuring cell of claim 1, wherein said ammonium salt is an admixture of ammonium salts.

4. An electrochemical measuring cell for determining ammonia or hydrazine in a fluid measuring sample present in the ambient, the measuring cell comprising:

a housing having an opening directed toward the sample to be measured and defining an electrolyte chamber;

a soluble electrolyte contained in said chamber;

a membrane mounted on said housing for closing off said chamber to the ambient and being permeable to ammonia and hydrazine;

a measuring electrode and a counter electrode disposed in said chamber so as to be in spaced relationship to each other;

said soluble electrolyte being an aqueous solution of a hygroscopic salt of an alkaline earth metal; and

,

said hygroscopic salt having a concentration in said aqueous solution for preventing solidification of said solution down to a temperature in the range of -10°

C. to -50°

C.

5. The electrochemical measuring cell of claim 4, wherein said hygroscopic salt has a cationic component and an anionic component;

said cationic component being selected from the group consisting of magnesium and calcium; and

, said anionic component being selected from the group consisting of a nitrate, bromide and chloride.

6. The electrochemical measuring cell of claim 1 or 4, further comprising:

at least said measuring electrode having a coating; and

,

said coating having an oxide of an element of the platinum metal group or a metal conductive oxide mixture of several elements of the platinum metal group.

7. The electrochemical measuring cell of claim 6, wherein said oxide constituent is selected from the group consisting of ruthenium dioxide, iridium dioxide and a mixture of said ruthenium dioxide and said iridium dioxide.

8. The electrochemical measuring cell of claim 6, wherein said measuring electrode is made of iridium and said coating comprises iridium dioxide.

9. The electrochemical measuring cell of claim 6, wherein said electrolyte has a neutral to acidic pH-value.

10. The electrochemical measuring cell of claim 9, said hygroscopic salt being selected from the group consisting of chloride and nitrate.

11. The electrochemical measuring cell of claim 6, said hygroscopic salt being selected from the group consisting of chloride and nitrate.

12. The electrochemical measuring cell of claim 6, further comprising an ion exchange membrane being disposed in said electrolyte between said measuring electrode and said counter electrode for preventing a hydroxide ion transport in said electrolyte.

13. The electrochemical measuring cell of claim 12, wherein said ion exchange membrane is made of perfluorosulfonated PTFE.

14. The electrochemical measuring cell of claim 12, said ion exchange membrane being a partition membrane mounted in said housing so as to extend between said measuring electrode and said counter electrode.

15. The electrochemical measuring cell of claim 12, wherein said measuring electrode has a surface, and said ion exchange membrane covers said surface of said measuring electrode.

16. The electrochemical measuring cell of claim 6, wherein said measuring electrode and said counter electrode both have the same composition.

17. The electrochemical measuring cell of claim 6, said housing having a wall and a portion of said wall being configured to include said counter electrode;

said portion of said housing comprising a porous membrane impermeable to said electrolyte and having a coating formed thereon facing toward said electrolyte to serve as said counter electrode;

said coating of said porous membrane defining a first surface facing toward said electrolyte and said porous membrane defining a second surface facing away from said electrolyte; and

said electrochemical measuring cell further comprising a filter covering said second surface; and

, said filter being adapted to accept ammonia.

18. The electrochemical measuring cell of claim 17, said filter including a housing and a charge of active charcoal contained in said housing.

19. The electrochemical measuring cell of claim 18, said charge of active charcoal being impregnated with zinc sulfate.

20. The electrochemical measuring cell of claim 18, said charge of active charcoal being impregnated with phosphoric acid.

21. The electrochemical measuring cell of claim 6, further comprising a reference electrode having the same composition as said measuring and counter electrode.