GB1568644A

GB1568644A - Combination electrode assemblies

Info

Publication number: GB1568644A
Application number: GB1103777A
Authority: GB
Original assignee: Owens Illinois Inc
Current assignee: OI Glass Inc
Priority date: 1976-03-17
Filing date: 1977-03-16
Publication date: 1980-06-04
Also published as: JPS52112385A; DK115777A; DE2706942A1

Description

(54) COMBINATION ELECTRODE ASSEMBLIES (71) We, OWENS-ILLINOIS, INC., a Corporation organized and existing under the laws of the State of Ohio, United States of America, of Toledo, State of Ohio, United States of America, (Assignee of PHILIP JACK BRENO), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to combination electrode assemblies.

Ion sensitive glass electrodes for measuring the aqueous solution concentration of hydrogen (i.e. pH), sodium ions, ammonium ions, potassium ions, and other ions have been known for many years. For instance, an electrode made of a glass composition selective to sodium ions is described in U.S.

Patent 2,829,090. A glass electrode for potassium ions is described in U.S. Patent 3,041,252 and pH sensitive glasses are described in U.S. Patents 3,806,440; 3,649,505; 2,756,203; or the text "Electrometric pH I)eterminations" by Roger G. Bates (John Wiley & Sons, Inc. New York) can be employed. The term "ion sensitive glass membrane" is used herein consistent with its usage in potentiometric electrode technology, and is intended to embrace a glass electrode tip, which provides a pair of surfaces between which charge transfer is affected.

In the past glass electrodes have been fabricated by blowing a thin membrane of the ion sensitive glass on the end of a stem of chemically resistant glass tube or by sealing (erg. by direct fusion or with adhesives) such an ion sensitive glass membrane to the end of the stem glass tube. More recently planar or fiat ion sensitive glass membranes have been developed as disclosed in commonly assigned U.S. Patent 3,806,440. These electrodes are used in conjunction with reference electrodes such as Si ver-silver chloride electrodes or calornet electrodes.

With the development of medical and industrial technology, there has come a need for combination electrodes containing both the ion senstive glass membrane and the reference electrode so that a single electrode assembly can be used to conduct the measure ment. This is almost a necessity in industrial and medical applications where the use of two electrodes is quite cumbersome for "micro" samples.

In the past such combination electrodes have of necessity been of inconveneient geometric shapes due to the inherent limitations in the glass forming processes used in the manufacture of such electrodes. In those prior combination electrodes such as in U.S.

Patents 3,880,737 and 3,399,667 the reference electrodes have been positioned at different locations on the combination electrode body so that it was always necessary to immerse a substantial portion of the combination electrode body into the test specimen. Other combination electrodes using a bulbous glass membrane with a reference electrode located on the side of the electrode body are available on the market. This immersion often required an inch or more of test solution depth to accomplish the measurement. Thus the combination electrode could only be used in those applications where there was a substantial volume of test solution and could not be used for measuring ion concentrations in small samples where only a thin film of sample is available.

The present invention seeks to overcome these disadvantages inherent in the prior art and provide a combination electrode of unique design and geometry having at least a portion of the liquid permeable porous plug of the restrained flow porous junction reference electrode and the ion sensitive membrane in coplanar relationship for conveneint contact with small smaple volumes and thin film applications.

Accordingly this invention provides a combination electrode assembly comprising an ion sensitive glass electrode and a reference electrode said assembly comprising a tubular envelope containing (a) said glass electrode, said glass electrode comprising a substantially planar, ion sensitive glass membrane positio ned for contact with a test specimen, said membrane being sealed to a chemically resistant glass tube to define an internal electrode cavity, said cavity containing. an internal electrolyte solution, and a first reference element positioned in said cavity in contact with said electrolyte solution, said reference element being adapted for electrical connection to an electrometer, and (b) a porous junction restrained flow reference electrode comprising a liquid permeable, porous plug being at least a portion of the surface of said plug and positioned for contact with said specimen in coplanar relationship with said glass membrane, said plug being in communication with a reservoir of a reference electrolyte solution and a second reference element positioned in said reservoir in electrical communication with said reference electrolyte, and adapted for electrical connection to said electrometer.Preferably the porous plug has a substantially planar surface which is positioned in coplanar relationship with the glass membrane, although a plug with a rounded or curved surface can also be used for this purpose.

Preferably also the restrained flow reference electrode is located in the tubular envelope.

The present invention will now be further described, with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional illustration of the combination electrode of the present invention; Fig. 2 is a broken away perspective view of the end of the electrode of the present invention illustrating the coplanar relationship of the reference electrode and the glass membrane; and Fig. 3 is a perspective view of the electrode assembly shown in Fig. 1.

Referring now to the drawings, reference numeral 10 generally illustrates the combination electrode comprising a rigid, tubular electrically insulating -housing 11 made of plastic, glass or other conventional material.

The lower end of housing 11 contains a resilient stopper 12 which is constructed of silicone rubber or similar material. Stopper 12 is provided with two apertures 12a and 12b.

Mounted and sealed within aperture 12a is a glass electrode comprising an inert, chemically resistant glass tube 13 having sealed to the lower end thereof a planar ion sensitive glass membrane 14 in the form of a flat disc.

The lower end of glass tube 13 is snugly engaged by resilient stopper 12 and held in position so that the lower end of ion sensitive glass membrane 14- is "even" or coplanar with - the lower end -of the stopper 12. The upper end of glass tube 13 is mounted in corresponding aperture 15a in a second resilient stopper 15 which stopper in turn fits snugly inside of housing 11.

Glass tube 13 contains a reservoir of aqueous buffered internal electrolyte solution 16 (e.g. 0-2M KCI) which is conventional and well known to those skilled in the art. Inside of glass tube 13 is mounted a first reference element 17 in the form of a silver wire. The lower end of reference element 17 is provided with a thin coating of silver chloride 1 7a and this coating is immersed in electrolyte 15.

Reference element 17 is held in position by apertured support 18 and 0 ring 19 inside of tube 13. 0 ring 19 functions to seal the electrolyte 16 in the lower end of the tube 13 and prevents its leakage to the upper portion of the electrode. The upper end of reference element 17 is electrically connected to insulated electrical cable 20 which is provided with electrical plug 21 adapted for connection with an electrometer. The inside of glass tube 13 above support 18 and below cap 40 is filled with a nonconductive plastic potting material 41 such as an epoxy resin to provide electrical insulation.

Mounted and sealed with aperture 12b in resilient stopper 12 is liquid permeable, porous plastic plug of porous polyethylene 30 having a volume porosity of 30% and an average pore size diameter of about 20 microns. The porous plug has substantially planar surface 30a which is coplanar with the lower end of glass membrane 14. Plug 30 is obtained from Porex Materials Corporation, Div. Glasrock Products, 7380 Bohannon Road, Fairburn, Georgia under tradename Porex.Porous plug 30 is constructed of porous ceramic, porous glass, sintered glass frit, porous plastic (e.g. such as used in felt tipped pens) bibulous matt or wick, or any of the other conventional liquid permeable materials used to construct porous junction restrained flow reference electrodes as set forth in Aids for the Analyst, Vol. 3, March 1955, pages 472-473; Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 11, page 385; Determination of pH by Roger G, Bates, Chapter 10, pages 318-320, (John Wiley & Sons); and Interpretation of pH and Cation Measurements, by G. Mattock and D. M. Band, pages 18-25..

Porous plug 30 terminates -above resilient stopper 12 and extends to the annular chamber defined between the housing 11 and the glass tube 13. This annular chamber contains a reference electrolyte solution 32 which can be a conventional- aqueous electrolyte solution 32- which can be a conventional aqueous electrolyte or e.g. aqueous solution of 4M KC1 or an aqueous gel which is 4M in KC1. Immersed in this reference electrolyte solution is a second reference element 33~in the form of silver wire which is provided at the lower end with a thin cdating of silver chloride 33a. Reference element 33 is supported at the upper end in aperture 15bof resilient- stopper 15.This is a conventional silver-silver chloride reference electrode and at least coating 33a must be immersed in electrolyte solution 32. The porous plug 30 together with the silver-silver chloride electrode 33 and 33a comprise a porous junction restrained flow-reference electrode.

Reference element 33 is electrically connected to an insulated electrical cable 34 which is provided with an electrical plug 35 which is adapted for connection with an electrometer. Cables 20 and 34 are shown as coaxial and are electrically shielded from one another. The upper end of housing 11 is fitted with a plastic cap 40 to enclose and contain the electrode assembly.

Preferably for economy in manufacture and efficiency of operation, the ion sensitive glass membrane is a disc of pH sensitive glass sealed to a chemically resistant glass tube by suitable adhesive or fusion sealing as by lampworking techniques.

The composition of the ion sensitive glass membrane or the chemically resistant glass tube are known in the art and form no part of the present invention. Such glass compositions and techniques for manufacture are disclosed in commonly assigned U.S. Patent 3,806,440, and Chapter 9 of "Determination of pH" by Roger G. Bates (John Wiley & BR< Sons, Inc.) 1974. For convenience in disclosure all patent documents and publications mentioned herein are incorporated by reference.

WHAT WE CLAIM IS: 1. A combination electrode assembly comprising a tubular envelope containing (a) an ion sensitive glass electrode, said glass electrode comprising a substantially planar ion sensitive glass membrane positioned for contact with a test specimen, said membrane being sealed to a chemically resistant glass tube to define an internal electrode cavity, said cavity containing an internal electrolyte solution, and a first reference element positioned in said cavity in contact with said electrolyte solution, said reference element being adapted for electrical connection to an electrometer, and (b) a porous junction restrained flow reference electrode comprising a liquid permeable, porous plug at least a portion of the surface of said plug being positioned for contact with said specimen and in coplanar relationship with said glass membrane, said plug being in communication with a reservoir of a reference electrolyte solution, and a second reference element positioned in said reservoir in electrical communication with said reference electrolyte, and adapted for electrical connection to said electrometer.

2. An assembly as claimed in claim 1 wherein the restrained flow reference electrode is rotated with in the tubular envelope.

3. An assembly as claimed in Claim 1 or 2 wherein said ion sensitive glass membrane is a pH sensitive glass.

4. An assembly as claimed in Claim 1 or 2 wherein said ion sensitive glass membrane is a sodium sensitive glass.

5. An assembly as claimed in Claim 1 or 2 wherein said ion sensitive glass membrane is a potassium sensitive glass.

6. An assembly as claimed in any one of Claims 1 to 5 in which the surface of the porous plug is substantially planar.

7. An assembly as claimed in any one of Claims 1 to 6 wherein said porous plug is a porous ceramic material.

8. An assembly as claimed in any one of Claims 1 to 6 wherein said porous plug is a porous plastic material.

9. An assembly as claimed in any one of Claims 1 to 8 wherein said second reference element is a silver/silver chloride electrode.

10. An electrode assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. silver-silver chloride reference electrode and at least coating 33a must be immersed in electrolyte solution 32. The porous plug 30 together with the silver-silver chloride electrode 33 and 33a comprise a porous junction restrained flow-reference electrode. Reference element 33 is electrically connected to an insulated electrical cable 34 which is provided with an electrical plug 35 which is adapted for connection with an electrometer. Cables 20 and 34 are shown as coaxial and are electrically shielded from one another. The upper end of housing 11 is fitted with a plastic cap 40 to enclose and contain the electrode assembly. Preferably for economy in manufacture and efficiency of operation, the ion sensitive glass membrane is a disc of pH sensitive glass sealed to a chemically resistant glass tube by suitable adhesive or fusion sealing as by lampworking techniques. The composition of the ion sensitive glass membrane or the chemically resistant glass tube are known in the art and form no part of the present invention. Such glass compositions and techniques for manufacture are disclosed in commonly assigned U.S. Patent 3,806,440, and Chapter 9 of "Determination of pH" by Roger G. Bates (John Wiley & BR< Sons, Inc.) 1974. For convenience in disclosure all patent documents and publications mentioned herein are incorporated by reference. WHAT WE CLAIM IS:

1. A combination electrode assembly comprising a tubular envelope containing (a) an ion sensitive glass electrode, said glass electrode comprising a substantially planar ion sensitive glass membrane positioned for contact with a test specimen, said membrane being sealed to a chemically resistant glass tube to define an internal electrode cavity, said cavity containing an internal electrolyte solution, and a first reference element positioned in said cavity in contact with said electrolyte solution, said reference element being adapted for electrical connection to an electrometer, and (b) a porous junction restrained flow reference electrode comprising a liquid permeable, porous plug at least a portion of the surface of said plug being positioned for contact with said specimen and in coplanar relationship with said glass membrane, said plug being in communication with a reservoir of a reference electrolyte solution, and a second reference element positioned in said reservoir in electrical communication with said reference electrolyte, and adapted for electrical connection to said electrometer.