WO2014204293A1

WO2014204293A1 - A double junction reference electrode

Info

Publication number: WO2014204293A1
Application number: PCT/MY2014/000096
Authority: WO
Inventors: Ahmad Mohd Rais; Woi PEI MENG; Nazmi AHMAD
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2013-06-19
Filing date: 2014-05-02
Publication date: 2014-12-24
Anticipated expiration: 2015-12-19
Also published as: MY164568A

Abstract

The present invention relates to a double junction reference electrode comprising: a porous plug (100); a leak protection cap (150); an external electrolyte (200); an internal reference (300); a silver-silver chloride electrode (400); a silver wire (500); a cap (600); and a casing (700); characterised in that the external electrolyte (200) further comprising halide-free electrolyte in gelled medium including a leak free protection seal (800) to provide internal sealing for the space between the porous plug (100) and the electrolytes and to cover the entire porous plug (100) inside with porous membrane. The present invention provides better performance of the reference electrode since leakage of the electrolyte is tackled with above mechanism.

Description

Title of Invention: A DOUBLE JUNCTION REFERENCE

ELECTRODE FIELD OF INVENTION

The present invention relates to a double junction reference electrode of a chemical sensor.

BACKGROUND OF THE INVENTION

One problem with reference electrodes is that, in order to ensure a stable voltage, it is necessary to maintain a steady flow of electrolyte through the porous frit. Thus there is a gradual contamination of the test solution with electrolyte ions. This can cause problems when trying to measure low levels of K, CI, or Ag, or when using other ISEs with which these elements may cause interference problems.

In order to overcome this difficulty the double junction reference electrode was developed. In this case the silver-silver chloride cell forms the inner element and this is inserted into an outer tube containing a different electrolyte which is then in contact with the outer test solution through a second porous frit. The outer filling solution is said to form a 'salt bridge' between the inner reference system and the test solution and is chosen so that it does not contaminate the test solution with any ions which would affect the analysis.

However, the available reference electrode of thechemical sensors suffer from chloride ion interference due to the leakage of reference electrode electrolyte. For single-junction reference electrode, leakage of reference electrolyte would contaminate the analyte. In silver-silver chloride reference electrode, the reference electrolyte is chloride (a halide). Chloride or other halide ions are main interfering ion in anion sensor such as nitrate and phosphate sensors and thus halide contamination from reference electrode is not desirable.

Therefore, there is a need for an invention which tackles halide leakage and interference on the reference electrode.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, the present invention provides a double junction reference electrode comprising: a porous plug (100) to allow external electrolyte to pass through; a leak protection cap (150) to encapsulate the porous plug ( 100) and to expose only the tip of the porous plug ( 100); an external electrolyte (200) to provide solid medium in order to support the internal reference and to provide ions for signal conduction; an internal reference (300) to provide constant concentration of chloride; a silver-silver chloride electrode (400) to provide reversible reduction- oxidation characteristic for electrochemical transduction; a silver wire (500) to conduct electrical signal and to provide substrate for silver-silver chloride electrode; a cap (600) to protect internal reference and to provide inlet for refilling; and a casing (700) to provide mechanical support for the porous plug (100), electrolytes and entire assembly; characterised in that the external electrolyte (200) further comprising halide- free electrolyte in gelled medium including a leak free protection seal (800) to provide internal sealing for the space between the porous plug ( 100) and the electrolytes and to cover the entire porous plug ( 100) inside with porous membrane.

[ 10] The above provision is advantageous as the use of the leak free protection seal (800) and the gelled medium of the external electrolyte (200) minimize the possibility of the electrolyte to leak thus jeopardizing the performance of the reference electrode as a whole.

[1 1 ] Leaking of chloride internal reference in reference electrode causes interference in the measurement and sensing of anionic analytes such as phosphate, nitrate and sulfate.

[12] The present invention provides a double junction reference electrode with negligible presence of chloride ion, which is suitable for portable and field application. The present invention provides the porous plug (100) is completely sealed to prevent leakage, externally the entire plug (100) is encapsulated only to expose the tip. The interior part of the plug ( 100) is fully covered with membrane, and the space between plug and body is sealed as well.

[13] The present invention also provides the internal reference is separated from the

analyte by the halide free solid external electrolyte (200). The state of the external electrolyte (200) which is in solid medium supports the internal reference as well.

[ 14] BRIEF DESCRIPTION OF THE DRAWINGS

[15] Figure lillustrates an embodiment of a double junction reference electrode of the present invention.

[ 16] Figure 2illustrates a flowchart of a method of preparing a double junction reference electrode of the present invention.

[ 17] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[18] Generally, the present invention relates to a double junction reference electrode

comprising: a porous plug ( 100) to allow external electrolyte to pass through; a leak protection cap (150) to encapsulate the porous plug (100) and to expose only the tip of the porous plug (100); an external electrolyte (200) to provide solid medium in order to support the internal reference and to provide ions for signal conduction; an internal reference (300) to provide constant concentration of chloride; a silver-silver chloride electrode (400) to provide reversible reduction-oxidation characteristic for electrochemical transduction; a silver wire (500) to conduct electrical signal and to provide substrate for silver-silver chloride electrode; a cap (600) to protect internal reference and to provide inlet for refilling; and a casing (700) to provide mechanical support for the porous plug ( 100), electrolytes and entire assembly; characterised in that the external electrolyte (200) further comprising halide-free electrolyte in gelled medium including a leak free protection seal (800) to provide internal sealing for the space between the porous plug (100) and the electrolytes and to cover the entire porous plug (100) inside with porous membrane. This is illustrated in Figure 1.

[ 19] The porous plug ( 100) comprises of at least one of the following materials: ceramic, alumina, zirconia, glass, cellulose, sol gel. The cap (600) comprises at least one of the following materials: epoxy, polyvinyl chloride, polycarbonate, polyester, glass, ceramic, zirconia, teflon, polyethylene. The material of the external electrolyte (200) gel is from hydroxyethyl methacrylate, or acrylamide, or glycidyl methacrylate, or methyl methacrylate, or butyl acrylate, or tetrahydrofurfuryl acrylate.The material ofthe leak free protection seal (800) is from acrylic, or cellulose acetate, or cellulose, or cellulose nitrate, or polyurethane, or polyvinyl chloride, or glass, or ceramic, or zirconia.The ion of the external electrolyte is from ion ofacetate; or trifluoroborate; or perchlorate; or nitrate; or sulfate; or phosphate; or phosphorate; or borate; or tri- fluroacetate; or styrene sulfate; or toluene sulfate, nafion, polyanethole sulfate, hex- afluorophosphate .

[20] As illustrated in Figure 2, in general, the method of preparing the solid state double junction comprising: sealing an external porous plug to expose only the tip (10); sealing an internal porous plug with porous material (20); preparing an external electrolyte gel (30); filling the internal reference electrolyte (40); capping a refill inlet with silver-silver electrode assembly (50); and testing electrolyte leak rate and sensor response signals (60).

[21] The encapsulation and sealing of the porous plug of the step ( 10) is started

withfreshly cut and cleared zirconia rod (2 mm) is secured at the narrow-end tip. Cellulose acetate solution (50μί, 5 wt ) is cast on the porous plug ( 100). Epoxy heat curable adhesive is applied onto the external porous plug, exposing only the tip. The plug assembly is treated with heat in the oven at 90°C for one hour.

[22] For more detail of the preparation of the external electrolyte (200), the procedure is started with hydroxyethyl methacrylate (5 mL, 0.1 M) lithium acetate and ammonium persulphate (trace) are homogeneously mixed ad filed into the plugged assembly, the assembly is clamped, immersed in water and heated at boiling temperature for one hour.

[23] Although the invention has been described with reference to particular embodiment, it is to be understood that the embodiment is merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiment that other arrangements may be devised without departing from the scope of the present invention as defined by the appended claims.

Claims

[Claim 1 ] A double junction reference electrode comprising:

a porous plug ( 100) to allow external electrolyte to pass through;

a leak protection cap (150) to encapsulate the porous plug ( 100) and to expose only the tip of the porous plug ( 100);

an external electrolyte (200) to provide solid medium in order to support the internal reference and to provide ions for signal conduction; an internal reference (300) to provide constant concentration of chloride;

a silver-silver chloride electrode (400) to provide reversible reduction- oxidation characteristic for electrochemical transduction;

a silver wire (500) to conduct electrical signal and to provide substrate for silver-silver chloride electrode;

a cap (600) to protect internal reference and to provide inlet for refilling; and

a casing (700) to provide mechanical support for the porous plug (100), electrolytes and entire assembly;

characterised in that

the external electrolyte (200) further comprising halide-free electrolyte in gelled medium including a leak free protection seal (800) to provide internal sealing for the space between the porous plug (100) and the electrolytes and to cover the entire porous plug ( 100) inside with porous membrane.

[Claim 2] A double junction reference electrode as claimed in Claim 1 , wherein the material of the external electrolyte (200) gel is from hydroxyethyl methacrylate, or acrylamide, or glycidyl methacrylate, or methyl methacrylate, or butyl acrylate, or tetrahydrofurfuryl acrylate.

[Claim 3] A double junction reference electrode as claimed in Claim 1 , wherein the material of the leak free protection seal (800) is from acrylic, or cellulose acetate, or cellulose, or cellulose nitrate, or polyurethane, or polyvinyl chloride, or glass, or ceramic, or zirconia.

[Claim 4] A double junction reference electrode as claimed in Claim 1, wherein the ion of the external electrolyte (200) is from ion of acetate; or triflu- oroborate; or perchlorate; or nitrate; or sulfate; or phosphate; or phosphorate; or borate; or trifluroacetate; or styrene sulfate; or toluene sulfate, nafion, polyanethole sulfate, hexafluorophosphate.

[Claim 5] A method of preparing the solid state double junction comprising: i. Sealing an external porous plug to expose only the tip ( 10);

ii. Sealing an internal porous plug with porous material (20);

iii. Preparing an external electrolyte gel (30);

iv. Filling the internal reference electrolyte (40);

v. Capping a refill inlet with silver-silver electrode assembly (50); and vi. Testing electrolyte leak rate and sensor response signals (60).