WO2010019026A2 - A charge-balanced planar reference electrode - Google Patents
A charge-balanced planar reference electrode Download PDFInfo
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- WO2010019026A2 WO2010019026A2 PCT/MY2009/000118 MY2009000118W WO2010019026A2 WO 2010019026 A2 WO2010019026 A2 WO 2010019026A2 MY 2009000118 W MY2009000118 W MY 2009000118W WO 2010019026 A2 WO2010019026 A2 WO 2010019026A2
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- WO
- WIPO (PCT)
- Prior art keywords
- reference electrode
- planar reference
- membrane
- charge
- electrode
- Prior art date
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/301—Reference electrodes
Definitions
- This invention relates to reference electrode used as half cell in potentiometric measurement. More specifically, the invention is directed to preparation of planar reference electrode containing highly lipophilic cation and anion components that function to balance the total of positive and negative charges approaching the chloride internal electrolyte.
- Electrochemical sensors specifically designed for the determination of a particular chemical species' concentration, more accurately described as its activity, in a solution. The determination is based on the fact that within certain limits, the potential of the electrode is directly proportional to the logarithm of, the chemical species' activity.
- These electrochemical sensors generally have sensing membranes specifically formulated for measuring the chemical species, of interest.
- One of the important properties of an electrochemical sensor is its selectivity. Meaning that, the results that are obtained are highly independent of other chemical species/ions which are present in the sample .being * tested.
- ISE ion-selective electrode
- ISEs have many applications in the fields of medicine, engineering, industrial processing control, education, and research. They are especially useful in clinical and environmental chemistry where large numbers of samples are processed.
- the sensing membrane is made of glass or various polymers such as polyvinyl chloride (PVC), silicone and, the like. Sensors using glass membranes such as sensors, for pH and sodium are relatively resistant to leaching under normal test conditions. Even when used in media such as human serum containing lipophilic agents, a glass-membrane type sensor can usually be cleaned and reconditioned thus extending the sensor's useful life..
- a polymeric-membrane type ISE is more sensitive to the conditions that cause failure, thus having a much shorter useful life as compared to glass-membrane type sensors. One of these conditions is the presence of interfering ions or substances.
- planar reference electrode that can be integrated on the same platform with chemical multi-sensors, whereby the stability of reference electrode is achieved through charge balancing mechanism.
- This invention relates to reference electrode used as half cell in potentiometric measurement. More specifically, the invention is directed to preparation of planar reference electrode containing highly lipophilic cation and anion components that function to balance the total of positive and negative charges approaching the chloride internal electrolyte.
- the method, setup, materials, polymer and molecules described, in. the invention are directed towards preparation of planar reference electrode based on charge-balanced mechanism.
- the reference electrode is to be integrated with chemical multi-sensors and to be deployed preferably for precision agriculture and environmental monitoring.
- Fig.1 illustrates the preferred embodiment of a charge-balanced planar reference electrode.
- Fig.2 illustrates an immobilized ammonium borate salts for charge-balanced reference electrode.
- Fig.3 illustrates chloride response from charge-balanced planar reference electrode versus conventional double-junction reference electrode.
- Fig.4 illustrates K+ response of a commercial potassium sensor versus charge-balanced planar reference electrode.
- Substrate 11 can be polyester, polycarbonate, printed circuit board or silicon wafer.
- the second layer is silver-silver chloride electrode 12, whereby the silver is electroplated or screen printed, and silver chloride is formed by chlorination of silver using ferric chloride. Electrical connection 13 to readout circuit is done using silver or copper wire.
- Internal layer 14 of the membrane is achieved by photo- polymerization of hydroyethyl methacrylate (HEMA) monomer and conditioning of the photocured membrane with 0.1 M potassium chloride.
- HEMA hydroyethyl methacrylate
- the charge-balanced membrane 15 is formed ⁇ by.photocun ⁇ g n-butylacrylate (nBA) containing 2% weight of immobilized ammonium borate.
- the top-most layer 16 is micro-porous organic polymer such as cellulose acetate for physical protection.
- EXAMPLE 1 Preparation of Ag/ AgC I electrode
- Silver-silver chloride electrode 12 is built either using screen printed silver paste or metallic silver disc. Screen printed silver is deposited by printing silver paste through fine mesh and curing in oven at 12O 0 C. Reproducible thickness (30 ⁇ 2 micrometer) of dry shiny silver can be manufactured using this method. Silver discs of 3 millimeter diameter and 0.8 millimeter thickness were cut out from 99.99% silver foil, commercially available, and polished with fine sand paper before chlorination.
- Chlorination of silver paste or metallic disc was achieved by ferric chloride solution (FeCI 3 1 M).
- FeCI 3 1 M ferric chloride solution
- N 2 nitrogen gas
- HEMA monomer was deposited onto the Ag/AgCI surface and photocured with ultraviolet light for 180 seconds under nitrogen gas (N 2 ) flow.
- Poly (HEMA) membrane formed was hydrated with concentrated salts solution of potassium chloride for 1 hour. This membrane functions as internal layer 14 as showed in Figure 1.
- the charge-balanced membrane 15 is built by depositing cocktail of n-butyl acrylate containing 2% by weight immobilized ammonium borate and 1% of commercial photo-initiator. Approximately 1 - 5 microliter of the cocktail yields the desired thickness of 50 to 100 micrometer of photocured membrane thickness.
- the top-most layer 16 serves as protection or insulation layer and it is microporous in nature.
- Organic polymer containing polar substituent such as cellulose acetate or cellulose nitrate can be used.
- Cocktail 0.5 to 2 microliter
- 10% cellulose acetate in tetrahydrofuran or dioxane is deposited on photocured charge-balanced membrane.
- the charge- balanced membrane 16 contains 2% by weight of immobilized ammonium borate salt illustrated in Fig. 2.
- the ammonium ion creates lipophilic sites in the membrane to neutralize incoming negative ions.
- borate ion creates negatively charged sites to neutralize incoming positively charged ions.
- the proposed planar reference electrode 10 does not require any liquid electrolyte or maintenance. It is suitable for field deployment of integrated multi-sensors for analysis of soil macronutrients and monitoring of ionic environmental contaminants. Stable reference electrode based on silver-silver chloride electrode can be achieved if the concentration of the chloride internal electrode can be made constant.
- Highly lipophilic borate and ammonium are doped in hydrophobic membrane such as acrylate. Equal amount of cations and anions can be transported from the analyte to the silver-silver chloride surface with appropriate ratio of highly lipophilic borate and ammonium. The lipophilic ammonium cation is immobilized to the polymer backbone in order to avoid leaching and loss of ions.
- inclination towards positive or negative slope can be compensated by addition of appropriate component to further balance the charge and flatten the slope.
- the fabricated charge-balanced planar reference electrode was characterized for stability over a wide concentration range, and coupled with commercial solid state chemical sensor for potentiometric response analysis.
Abstract
This invention relates to reference electrode used as half cell in potentiometric measurement. More specifically, the invention is directed to preparation of planar reference electrode containing highly lipophilic cation and anion components that function to balance the total of positive and negative charges approaching the chloride internal electrolyte.
Description
A CHARGE-BALANCED PLANAR REFERENCE ELECTRODE
FIELD OF THE INVENTION
This invention relates to reference electrode used as half cell in potentiometric measurement. More specifically, the invention is directed to preparation of planar reference electrode containing highly lipophilic cation and anion components that function to balance the total of positive and negative charges approaching the chloride internal electrolyte.
BACKGROUND OF THE INVENTION
Detection of various chemical species such as cation, anions, electrophilic or neucleophilic particles normally uses electrochemical sensors specifically designed for the determination of a particular chemical species' concentration, more accurately described as its activity, in a solution. The determination is based on the fact that within certain limits, the potential of the electrode is directly proportional to the logarithm of, the chemical species' activity. These electrochemical sensors generally have sensing membranes specifically formulated for measuring the chemical species, of interest. One of the important properties of an electrochemical sensor is its selectivity. Meaning that, the results that are obtained are highly independent of other chemical species/ions which are present in the sample .being * tested.
Selective membrane sensors originated in the basic pH glass membrane electrode. The advent of crystal and liquid membrane sensors led to the
ISEs have many applications in the fields of medicine, engineering, industrial processing control, education, and research. They are especially useful in clinical and environmental chemistry where large numbers of samples are processed.
Basically, the sensing membrane is made of glass or various polymers such as polyvinyl chloride (PVC), silicone and, the like. Sensors using glass membranes such as sensors, for pH and sodium are relatively resistant to leaching under normal test conditions. Even when used in media such as human serum containing lipophilic agents, a glass-membrane type sensor can usually be cleaned and reconditioned thus extending the sensor's useful life.. A polymeric-membrane type ISE, on the other hand, is more sensitive to the conditions that cause failure, thus having a much shorter useful life as compared to glass-membrane type sensors. One of these conditions is the presence of interfering ions or substances.
Various attempts have been made in the past to couple multiple sensors together and to prolong sensor life.
Therefore, what is needed is an ISE that- has a longer ϋselife and better performance than ISEs currently available. The use life of an ISE is defined as the length of time an ISE continues to function properly and reliably for its intended use. Hence, we propose planar reference electrode that can be integrated on the same platform with chemical multi-sensors, whereby the stability of reference electrode is achieved through charge balancing mechanism.
SUMMARY OF THE INVENTION
This invention relates to reference electrode used as half cell in potentiometric measurement. More specifically, the invention is directed to preparation of planar reference electrode containing highly lipophilic cation and anion components that function to balance the total of positive and negative charges approaching the chloride internal electrolyte.
It is an object of the present invention to provide a planar reference electrode that doesn't require the , use of liquid electrolytes or any maintenance.
It is another object. of the present invention to provide a planar reference electrode that is miniaturized and integrated on the same planar platform with the multi-sensors. It is yet another object of the present invention to provide a planar 'reference electrode that is leak-free and doesn't suffer from loss ofϊiόnic electrolytes.
It is a further object of the present invention to provide a planar reference electrode that is durable and suitable for field deployment.
The method, setup, materials, polymer and molecules described, in. the invention are directed towards preparation of planar reference electrode based on charge-balanced mechanism.
The reference electrode is to be integrated with chemical multi-sensors and to be deployed preferably for precision agriculture and environmental monitoring.
All of the advantages of the present invention will be clear upon review of the detailed description, drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.1 illustrates the preferred embodiment of a charge-balanced planar reference electrode.
Fig.2 illustrates an immobilized ammonium borate salts for charge-balanced reference electrode.
Fig.3 illustrates chloride response from charge-balanced planar reference electrode versus conventional double-junction reference electrode.
Fig.4 illustrates K+ response of a commercial potassium sensor versus charge-balanced planar reference electrode.
DETAILED DESCRPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the proposed charge-balanced reference electrode 10 is described in Fig. 1. Substrate 11 can be polyester, polycarbonate, printed circuit board or silicon wafer. The second layer is silver-silver chloride electrode 12, whereby the silver is electroplated or screen printed, and silver chloride is formed by chlorination of silver using ferric chloride. Electrical connection 13 to readout circuit is done using silver or copper wire. Internal layer 14 of the membrane is achieved by photo- polymerization of hydroyethyl methacrylate (HEMA) monomer and conditioning of the photocured membrane with 0.1 M potassium chloride. The charge-balanced membrane 15 is formed^by.photocunηg n-butylacrylate (nBA) containing 2% weight of immobilized ammonium borate. The top-most layer 16 is micro-porous organic polymer such as cellulose acetate for physical protection.
EXAMPLE 1 Preparation of Ag/ AgC I electrode Silver-silver chloride electrode 12 is built either using screen printed silver paste or metallic silver disc. Screen printed silver is deposited by printing silver paste through fine mesh and curing in oven at 12O0C. Reproducible thickness (30 ± 2 micrometer) of dry shiny silver can be manufactured using this method. Silver discs of 3 millimeter diameter and 0.8 millimeter thickness were cut out from 99.99% silver foil, commercially available, and polished with fine sand paper before chlorination.
Chlorination of silver paste or metallic disc was achieved by ferric chloride solution (FeCI3 1 M). The solution was dropped onto the surface of printed or metallic silver and left for 2 minutes under nitrogen gas (N2) flow for to form the Ag/AgCI electrode shown in Fig. 1 and rinsed with deionozed water, wiped and dried at ambient temperature.
Preparation of internal reference layer
After the silver-silver choride electrode Ag/AgCI 13 layer growths, HEMA monomer was deposited onto the Ag/AgCI surface and photocured with ultraviolet light for 180 seconds under nitrogen gas (N2) flow. Poly (HEMA) membrane formed was hydrated with concentrated salts solution of potassium chloride for 1 hour. This membrane functions as internal layer 14 as showed in Figure 1.
Preparation of charge-balanced membrane
The charge-balanced membrane 15 is built by depositing cocktail of n-butyl acrylate containing 2% by weight immobilized ammonium borate and 1% of commercial photo-initiator. Approximately 1 - 5 microliter of the
cocktail yields the desired thickness of 50 to 100 micrometer of photocured membrane thickness.
Preparation of insulation layer
The top-most layer 16 serves as protection or insulation layer and it is microporous in nature. Organic polymer containing polar substituent such as cellulose acetate or cellulose nitrate can be used. Cocktail (0.5 to 2 microliter) of 10% cellulose acetate in tetrahydrofuran or dioxane is deposited on photocured charge-balanced membrane. The charge- balanced membrane 16 contains 2% by weight of immobilized ammonium borate salt illustrated in Fig. 2. The ammonium ion creates lipophilic sites in the membrane to neutralize incoming negative ions. Likewise borate ion creates negatively charged sites to neutralize incoming positively charged ions.
Chloride (Cl ) response from charge-balanced planar reference electrode versus conventional double-junction reference electrode
The response of chloride from different concentration of potassium chloride solutions produced by charge-balanced planar reference electrode versus commercially available double-junction reference electrode is illustrated in Fig. 3. The result shows that the disclosed charge-balanced planar reference electrode shows negligible potential different across a wide range of analyte activities.
Potassium ion (K+) response of a commercial potassium sensor versus charge-balanced planar reference electrode
The response of potassium ion using commercial solid state potassium sensor versus charge-balanced planar reference electrode is described in Fig. 4. The result shows that the disclosed charge-balanced reference electrode can be used in potentiometric measurement to produce the expected response and sensitivity of the commercial reference electrode.
Additionally, the proposed planar reference electrode 10 does not require any liquid electrolyte or maintenance. It is suitable for field deployment of integrated multi-sensors for analysis of soil macronutrients and monitoring of ionic environmental contaminants. Stable reference electrode based on silver-silver chloride electrode can be achieved if the concentration of the chloride internal electrode can be made constant.
Highly lipophilic borate and ammonium are doped in hydrophobic membrane such as acrylate. Equal amount of cations and anions can be transported from the analyte to the silver-silver chloride surface with appropriate ratio of highly lipophilic borate and ammonium. The lipophilic ammonium cation is immobilized to the polymer backbone in order to avoid leaching and loss of ions.
Alternatively, inclination towards positive or negative slope can be compensated by addition of appropriate component to further balance the charge and flatten the slope. The fabricated charge-balanced planar reference electrode was characterized for stability over a wide concentration range, and coupled with commercial solid state chemical sensor for potentiometric response analysis.
Although the preferred embodiments of the present invention have been described herein, the above descriptions are merely illustrative. Further
modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.
Claims
1. A planar reference electrode 10 comprising: a substrate 11 as a first layer; an electrode 12 as a second layer; an electrode connecting part 13 to connect the electrode to a read out circuit; an internal reference layer 14; a charge balanced membrane 15; an insulating membrane 16; characterised in that the charge balanced membrane 15 is immobilized with charge balancing species.
2. The planar reference electrode 10 according to claim 1 characterised in that the charge balancing species include cations and anions having similar size and migration rate.
3. The planar reference electrode 10 according to claim 1 characterised in that the charge balancing species is lipophilic ammonium and borate ions.
4. The planar reference electrode 10 according to claim 4 characterised in that the ammonium borate salts of formula 1
is used to create lipophilic ionic sites, and to achieve balanced charge at silver-silver chloride reference surface.
5. The planar reference electrode 10 according, to claim 3 or claim. 4 characterised in that the ammonium ion side chain R1, R2 and R3 is an alkyl group.
6. The planar reference electrode 10 according to claim 5 characterised in that the alkyl group for R1 and R2 is preferably heptyl, (CH2)6CH3 or undecyl, (CH2)i0CH3.
7. The planar reference electrode 10 according to claim 6 characterised in that the side chain R3 is haloalkyl.
8. The planar reference electrode 10 according to claim 7 characterised in that the haloalkyl is preferably fluoroalkyl
9. The planar reference electrode 10 according to claim 8 characterised in that the fluoroalkyl is preferably CH2(CF2)7CF3.
10. The planar reference electrode 10 according to claim according to claim 1 characterised in that the charge balancing membrane 15 is built by depositing cocktail of n-butyl acrylate containing preferably 2% by weight immobilized ammonium borate and 1% of commercial photo-initiator.
11. The planar reference electrode 10 according to claim 1 characterised in that the charge balancing membrane 15 thickness is preferably within the range of 50 to 100 micrometer.
12. The planar reference electrode 10 according to claim 1 characterised in that the insulating membrane is microporous.
13. The planar reference electrode 10 according to claim 1 characterised in that the insulating membrane 16 is preferably made from organic polymer containing polar substituent.
14. The planar reference electrode 10 according to claim 13 characterised in that the organic polymer is selected from cellulose acetate or cellulose nitrate.
15. The planar reference electrode 10 according to claim 1 characterised in that the substrate 11 is selected from the list of polyester, polycarbonate, printed circuit board or silicon wafer.
16. The planar reference electrode 10 according to claim 1 characterised in that the electrode connecting part 13 is made of copper or silver.
17. The planar reference electrode 10 according to claim 1 characterised in that the internal layer 14 of the membrane is preferably prepared by photo-polymerization of hydroyethyl methacrylate (HEMA) monomer and conditioning of the photocured membrane with 0.1 M potassium chloride.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| MYPI20083068 | 2008-08-13 | ||
| MYPI20083068 | 2008-08-13 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| WO2010019026A2 true WO2010019026A2 (en) | 2010-02-18 |
| WO2010019026A3 WO2010019026A3 (en) | 2010-06-17 |
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| Application Number | Title | Priority Date | Filing Date |
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| PCT/MY2009/000118 WO2010019026A2 (en) | 2008-08-13 | 2009-08-13 | A charge-balanced planar reference electrode |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113528841A (en) * | 2021-07-26 | 2021-10-22 | 中南大学 | Method for removing impurity metals from waste circuit board copper powder through ball milling |
| CN114455775A (en) * | 2022-01-05 | 2022-05-10 | 江苏合普环保科技有限公司 | Bioengineering bacterium treatment method for high-salt wastewater in aldehyde production |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4214968A (en) * | 1978-04-05 | 1980-07-29 | Eastman Kodak Company | Ion-selective electrode |
| KR20020030638A (en) * | 2000-10-19 | 2002-04-25 | 차근식 | Microchip-type oxygen gas sensor based on differential potentiometry |
| US20050023153A1 (en) * | 2003-07-09 | 2005-02-03 | Auburn University | Reversible electrochemical sensors for polyions |
| US20060060471A1 (en) * | 2002-11-28 | 2006-03-23 | Drew Scientific Limited | Multi-ionophore membrane electerode |
-
2009
- 2009-08-13 WO PCT/MY2009/000118 patent/WO2010019026A2/en active Application Filing
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4214968A (en) * | 1978-04-05 | 1980-07-29 | Eastman Kodak Company | Ion-selective electrode |
| KR20020030638A (en) * | 2000-10-19 | 2002-04-25 | 차근식 | Microchip-type oxygen gas sensor based on differential potentiometry |
| US20060060471A1 (en) * | 2002-11-28 | 2006-03-23 | Drew Scientific Limited | Multi-ionophore membrane electerode |
| US20050023153A1 (en) * | 2003-07-09 | 2005-02-03 | Auburn University | Reversible electrochemical sensors for polyions |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113528841A (en) * | 2021-07-26 | 2021-10-22 | 中南大学 | Method for removing impurity metals from waste circuit board copper powder through ball milling |
| CN114455775A (en) * | 2022-01-05 | 2022-05-10 | 江苏合普环保科技有限公司 | Bioengineering bacterium treatment method for high-salt wastewater in aldehyde production |
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| Publication number | Publication date |
|---|---|
| WO2010019026A3 (en) | 2010-06-17 |
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