Free chlorine sensor

• US 7,790,006 B2
• Filed: 09/13/2004
• Issued: 09/07/2010
• Est. Priority Date: 05/03/2002
• Status: Active Grant

• Current Assignee: Rosemount Analytical, Inc. (Emerson Electric Company)
• Original Assignee: Rosemount Analytical, Inc. (Emerson Electric Company)
• Inventors: Garretson, Joshua Steven, Xu, Jishou, Feng, Chang-Dong
• Primary Examiner(s): Huff; Mark F
• Assistant Examiner(s): Alam; Rashid
• Application Number:
  US10/939,866
• Publication Number:
  US 20050029103A1
• Time in Patent Office: 2,185 Days
• Field of Search: 204/415, 204/403.4, 204/449, 205/775, 73/232, 514/44
• US Class Current: 204/432
• CPC Class Codes: G01N 27/404 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
• CPC Class Codes: G01N 27/4045 for gases other than oxygen
• CPC Class Codes: G01N 33/0049 Halogenated organic compounds

Abstract

A free chlorine measurement system and sensor are provided. In accordance with one aspect of the invention, the sensor has a porous working electrode disposed in an electrolyte proximate a porous membrane. The membrane allows free chlorine therethrough where it is reduced and generates a current. The current is related to the free chlorine concentration. The internal electrolyte solution is pH stabilized with a long-term pH stabilizer that has a solubility in water at room temperature between about 1.2 moles/liter and about 0.001 moles/liter. The stabilizer can be an acid or a base depending on whether the pH is to be stabilized at a relatively low value or a relatively high value respectively.

Claims

1. An amperometric sensor for measuring free chlorine in a solution, the free chlorine being in the form of hypochlorite ion and hypoclorus acid, the sensor comprising:

a sensor body;

an electrolyte disposed within the sensor body;

a membrane coupled to the sensor body and adapted to pass hypochlorite ion and hypoclorus acid therethrough into the sensor body;

a reference electrode disposed in the electrolyte;

a porous working electrode disposed proximate the membrane, the porous working electrode being constructed from a noble metal; and

a solid phase long-term pH stabilizer disposed in the electrolyte, the stabilizer being an acid selected from the group consisting of succinic acid, adipic acid, suberic acid and boric acid, having a solubility in water, at about 25 degrees Celsius, between about 1.2 Moles/liter and about 0.001 Moles/liter, the stabilizer acting to maintain the pH in the electrolyte at a level to cause substantially all hypochlorite ion passing through the membrane to become hypoclorus acid.

2. The sensor of claim 1, wherein the non-compact form is a Gas Diffusion Electrode.

3. The sensor of claim 2, wherein the Gas Diffusion Electrode is loaded with the noble metal in a powdered form.

4. The sensor of claim 3, wherein the noble metal is platinum.

5. The sensor of claim 4, wherein the platinum is loaded onto the Gas Diffusion Electrode at approximately 80% Pt/C.

6. The sensor of claim 2, wherein the Gas Diffusion Electrode includes a carbon cloth.

7. The sensor of claim 1, wherein the non-compact form of the working electrode is a mesh.

8. The sensor of claim 7, wherein the working electrode is constructed from gold mesh.

9. The sensor of claim 1, wherein the membrane is hydrophilic.

10. A system for monitoring free chlorine concentration in a solution, the free chlorine being in the form of hypochlorite ion and hypoclorus acid, the system comprising:

a free chlorine amperometric sensor including;

a sensor body;

an electrolyte disposed within the sensor body;

a membrane coupled to the sensor body and adapted to pass hypochlorite ion and hypoclorus acid therethrough into the sensor body;

a reference electrode disposed in the electrolyte;

a porous working electrode disposed proximate the membrane, the porous working electrode being constructed from a noble; and

a solid phase long-term pH stabilizer disposed in the electrolyte, the stabilizer being an acid selected from the group consisting of succinic acid, adipic acid, suberic acid and boric acid, having a solubility in water, at about 25 degrees Celsius, between about 1.2 Moles/liter and about 0.001 Moles/liter, the stabilizer actin to maintain the pH in the electrolyte at a level to cause substantially all hypochlorite ion passing through the membrane to become hypoclorus acid; and

an analysis device coupled to the reference electrode and the working electrode, the analysis device adapted to provide a sufficient working potential and to measure a current flowing between the reference electrode and working electrode and provide an indication of free chlorine concentration based on the current.

11. The system of claim 10, wherein the analysis device is a transmitter.