Reference electrode and method of making it

Claim 2

A miniature reference electrode providing both electrical connection and a liquid junction between a reference liquid solution and a solution to be tested comprising: cup means including a cavity to hold the reference liquid solution having a sample contacting orifice at one end and an opposed open second end, said orifice being defined by a peripheral sidewall; a membrane comprising cellulose acetate extending across said orifice and interdigitatedly anchored to said peripheral sidewall; means for applying a generally fixed control potential to said reference liquid solution; and means for hermetically closing the second open en of said cavity.

Claim 3

A miniature reference electrode as in claim 1, wherein said cup means comprises a dielectric thermoplastic material.

Claim 4

A miniature reference electrode as in claim 2 wherein said cellulose acetate membrane is formed in situ from a composition comprising: (a) from about 0.3% to about 5.0% by weight cellulose acetate having an acetyl content of from about 25% to about 50%; (b) from about 70% to about 90% by weight of a first polar organic solvent, said first solvent being capable of dissolving (a) and at least partially dissolving the thermoplastic material of said cup means; (c) from about 1% to about 5% by weight of an inorganic metal salt selected from the group consisting of lithium, sodium. magnesium, calcium, zinc, potassium, aluminum and copper salts; (d) from about 5% to about 15% by weight of a C 1 to C 10 alcohol capable of dissolving (c) and miscible in (b); and (e) optionally, from about 1% to about 5% of a flexibility improving agent selected from C 5 -C 10 cyclic hydrocarbons; C 5 -C 10 cyclic monohydric alcohols and lower C 1 -C 4 alkyl esters of aliphatic and aromatic carboxylic acids, based on the weight of the overall composition.

Claim 5

A miniature reference electrode as in claim 1, wherein said cup means comprises an acrylic thermoplastic material.

Claim 6

A miniature reference electrode as in claim 1 wherein said means for applying a generally fixed control potential comprises an electrode disposed in said cavity.

Claim 7

A miniature reference electrode as in claim 5, wherein said electrode comprises a Ag/AgCl electrode and said reference liquid solution comprises from about 1.0 to about 10.0 mM KCl in from about 50 to about 150 mM saline.

Claim 8

In a miniature reference electrode half-cell, a method for making a reference liquid junction membrane for providing an electrical connection and a liquid junction between a reference liquid solution and a solution to be tested comprising: (a) providing a cup means of a dielectric thermoplastic material including a cavity to hold the reference liquid solution having a sample contacting orifice at one end and an opposed second end, said orifice being defined by a peripheral sidewall; (b) preparing a liquid junction membrane composition by (1) dissolving about 0.3% to about 5.0% by weight of cellulose acetate having an acetyl content of from about 25% to about 50% in 70% to 90% by weight of a first polar organic solvent capable of at least partially dissolving said thermoplastic material; (2) dissolving from about 1% to about 5% by weight of an inorganic metal salt selected from Li, Na, Mg, Ca, Zn, K, Al, Cu salts in from about 5% to about 15% by weight of a second solvent comprising a C 1 to C 10 alcohol; (3) mixing the solutions of step (1) and (2) together; (4) thereafter, optionally adding from about 1% to about 5% by weight of a flexibility improving agent selected from C 5 -C 10 cyclic hydrocarbons; C 5 -C 10 cyclic monohydric alcohols and lower C 1 -C 4 alkyl esters of aliphatic and aromatic carboxylic acids, based on the weight of the overall composition, to the mixture of step (3) to form the membrane composition; (c) depositing a drop of said liquid junction membrane composition through said cavity and into said orifice in contact with the peripheral sidewall; (d) curing and interdigitatedly anchoring said membrane to said orifice by permitting the solvents to evaporate until membrane formation is substantially complete; and (e) thereafter contacting said membrane with a solvent for said metal salt to create micropores therein by removal of said metal salt from the membrane.

Claim 9

In a miniature reference electrode half-cell, a method for making a reference liquid junction membrane for providing an electrical connection and a liquid junction between a reference liquid solution and a solution to be tested comprising: (a) providing a cup means of a dielectric thermoplastic material including a cavity to hold the reference liquid solution having a sample contacting orifice at one end and an opposed second end, said orifice being defined by a peripheral sidewall; (b) preparing a liquid junction membrane composition by (1) dissolving about 0.3% to about 5.0% by weight of cellulose acetate having an acetyl content of from about 25% to about 50% in 70% to 90% by weight of a first polar organic solvent capable of at least partially dissolving said thermoplastic material; (2) dissolving from about 1% to about 5% by weight of an inorganic metal salt selected from Li, Na, Mg, Ca, Zn, K, Al, Cu salts in from about 5% to about 15% by weight of a second solvent comprising a C 1 to C 10 alcohol; (3) mixing the solutions of step (1) and (2) together; (4) thereafter, optionally adding from about 1% to about 5% by weight of a flexibility improving agent selected from C 5 -C 10 cyclic hydrocarbons; C 5 -C 10 cyclic monohydric alcohols and lower C 1 -C 4 alkyl esters of aliphatic and aromatic carboxylic acids, based on the weight of the overall composition, to the mixture of step (3) to form the membrane composition; (c) depositing a drop of said liquid junction membrane composition through said cavity and into said orifice in contact with the peripheral sidewall; (d) curing and interdigitatedly anchoring said membrane to said orifice by permitting the solvents to evaporate until membrane formation is substantially complete; and (e) thereafter contacting said membrane with a solvent for said metal salt to create micropores therein by removal of said metal salt from the membrane.