WO2012067490A1

WO2012067490A1 - Ion selective electrode

Info

Publication number: WO2012067490A1
Application number: PCT/MY2011/000140
Authority: WO
Inventors: Ahmad Mohd Rais; Alva Sagir; Abd Rashid Norazah; Abd Aziz Aiman Sajidah
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2010-11-15
Filing date: 2011-06-23
Publication date: 2012-05-24
Anticipated expiration: 2013-05-15

Abstract

The present invention relates to ion selective electrode (ISE) (10) for potentiometric measurement. The ion selective electrode (10) for electrochemical sensing comprising a substrate (12), a conductor layer (14); a solution cast conductive polymer transducer layer (16) to convert chemical concentration to electrical signal; a sensing membrane (18) having ion recognizing molecule, lipophilic salt and lipophilic organic polymer to selectively detect ionic analyte; a retaining dam (20) to contain a cocktail of the sensing membrane (18); characterised in that, the solution cast conductive polymer transducer layer (16) comprises of; a bisphenol A propoxylate diglycidyl ether, a purified diamine binder; a polymer; an organic sulfonate salt; and a polar solvent. The present invention also provides methods of making and using such ISE sensors.

Description

Title of Invention: ION SELECTIVE ELECTRODE Technical Field

Technical Field

[1] The present invention relates to ion selective electrode for potentiometric measurement .

Background Art

[2] Ion selective electrode (ISE) has been widely employed as chemical sensors in potentiometric measurement. The ISE sensor comprises selective polymeric membrane, electrochemical reduction-oxidation (redox) transducer, conducting film or wire and a reference electrode. Reversible redox transducer is often used to convert chemical potential to electrical signal. Silver-silver chloride transducer is the most choice but conducting polymer, especially polypyrrole (PPy), is becoming more common.

Polypyrrole has been the most widely used due to its ease of use, good sensor characteristics and mechanical strength.

[3] Polypyrrole (PPy) is often deposited on electrode surface via electropolymerization of the doped pyrrole monomer electrolyte. The underlying layer preferably has clean surface and uniform thickness of screen-printed carbon. Electropolymerization of pyrrole on metallic surface is less common. Although metals like silver, copper and gold are better conductor for signal transmission, formation of polypyrrole transducer layer on metal electrode surface can take hours.

[4] However, electropolymerization is sometime not possible due to several reasons

[5] such as, the electrode is too small and the electrical contacts are inaccessable for contacting, electrical shorting occurs when the unprotected contact pads are immersed in the pyrrole monomer electrolyte solution, the electrode has metallic surface wherein electropolymerization takes hours to complete.

[6] Therefore, in view of the above problems, it is desirable to further develop an

improved ion selective electrode and method for preparing the same for electrochemical sensing.

Disclosure of Invention

Technical Problem

[7]

Technical Solution

[8]

Summary [9] According to a first aspect of the invention, there is provided a Ion selective electrode

10 for electrochemical sensing comprisinga substrate 12, a conductor layer 14; a solution cast conductive polymer transducer layer 16 to convert chemical concentration to electrical signal; a sensing membrane 18 having ion recognizing molecule, lipophilic salt and lipophilic organic polymer to selectively detect ionic analyte; a retaining dam 20 to contain a cocktail of the sensing membrane 18; characterised in that, the solution cast conductive polymer transducer layerl6 comprises of ; a bisphenol A propoxylate diglycidyl ether, a purified diamine binder; a polymer; an organic sulfonate salt; and a polar solvent.

[10] The provision of the solution cast is advantageous as it results in homogenously form solution cast polymer transducer layer 16.

[11] Accordingly, the solution cast conductive polymer transducer layer 16 wherein the polymer is at least one or combination of polypyrrole, polythiophene, polyaniline.

Preferably, the polymer is polypyrrole.

[12] Accordingly, the solution cast conductive polymer transducer layer 16 contains 3 to

30 weight percent of Bisphenol A propoxylate diglycidyl ether-diamine binder in polar solvent.

[13] Accordingly, the diamine binder is selected from at least one or combination of m - xylylenediamine, /?-xylylenediamine, /?-phenylenediamine, 1,3-diaminopropane, 1 ,4-diaminobutane.

[14] Accordingly, the conductor layer 14 is selected from the list of carbon, silver, copper, gold, platinum or combination thereof. Preferably, the conductor layer 14 is silver

[15] Accordingly, the polar solvent is selected from the list of methanol, ethanol, n - propanol, wo-propanol, tetrahydrofuran, diethylether, dimethylsulfoxide, acetonitrile, acetone, water or combination thereof.

[16] Accordingly, the retaining dam 20 is screen-printed paste of Bisphenol A propoxylate diglycidyl ether-diamine paste.

[17] Accordignly, the solution cast conductive polymer transducer layer 16 comprises 3 to 10 percent polypyrrole, 1 to 5 percent Bisphenol A propoxylate diglycidyl ether, 1 to 5 percent diamine crosslinker and 2 to 5 percent /?ora-toluene sulfonic acid, all by weight, in polar solvent.

[18] Advantageously, the solution cast polymer transducer layer 16 minimizes the needs of continuous stirring during preparation of the transducer layer.

[19] Advantageously, the ion selective electrode 10 is producible in shorter time.

[20] Advantageously, the ion selective electrode 10 gives excellent electrochemical characteristics.

[21] Advantageously, the ion selective electrode 10 is usable as pH sensor, potassium

sensor, nitrate sensor or the like. Description of Drawings

[22] Figure 1 : illustrates Ion selective electrode with solvent cast transducer.

[23] Figure 2 : illustrates Solvent cast conductive polypyrrole with Bisphenol A

propoxylate diglycidyl ether- n-xylylene diamine binder.

[24] Figure 3 : illustrates pH ISE with cast polypyrrole transducer.

[25] Figure 4 : illustrates Potassium ISE with cast polypyrrole transducer.

[26] Figure 5 : illustrates Nitrate ISE with cast polypyrrole transducer

[27]

[28] Detailed description of the present invention

[29] The present invention relates to ion selective electrode 10 with solvent cast polymer transducer layer 16.

[30] As illustrated in Figure 1, the Ion selective electrode 10 comprising a substrate 12 underlaying a conductor layer 14; a solution cast conductive polymer transducer layer 16 to convert chemical concentration to electrical signal; a sensing membrane 18 having ion recognizing molecule, lipophilic salt and lipophilic organic polymer to selectively detect ionic analyte; a retaining dam 20 to contain a cocktail of the sensing membrane 18. The solution cast conductive polymer transducer layer 16 comprises of ; a bisphenol A propoxylate diglycidyl ether, a purified diamine crosslinker; a polymer; an organic sulfonate salt; and a polar solvent.

[31] In one example of the present invention, a composition of homogenous PPy cocktail targeted for solvent casting application is used for preparing the transducer 16. The cocktail contains Bisphenol A propoxylate diglycidyl ether with primary diamine crosslinkers that can be cured at ambient temperature. The cocktail is either pipetted or drop coated onto ion selective electrode 10 (ISE) surface, preferably clean screen- printed carbon surface, to form reproducible PPy transducer layer 16 that gives excellent electrochemical characteristics.

[32] In a preferred embodiment, silver is used as conductor underlying layer 14 and wire trace is first screen printed followed by screen printing of carbon layer. The screen printed carbon surface is cleaned by sonication and the solution cast polypyrrole tranducer cocktail containing 5 weight percent of Bisphenol A propoxylate diglycidyl ether resin and m-xylylenediamine crosslinker in ethanol was drop coated onto the clean carbon surface forming the solution cast polypyrrole transducer layer 16. The solution cast polypyrrole transducer layer 16 was dried at room temperature under continuous flow of nitrogen.

[33] When immersion of electrode contacts into electrolyte results in shorting or when the electrode contacts are inaccessible for electropolymerization, drop coating or spin coating method is a technique of choice for introducing polypyrrole transducer layer 16 for bio-chemical sensors. PPy cocktail 22 is perferably homogenous, not sticky or too viscous to give reproducible results and facilitate dispensing. Moreover, it is important that the binding (epoxy binder) component be able hold the poplypyrrole active component together while maintaining its conductive characteristic and reduction- oxidation properties. On the contrary, the epoxy binder is electrically insulating and excessive use of it yields layer with high impedance and fails to conduct electrical signal.

[34] Commercially available epoxy resin, Bisphenol A propoxylate diglycidyl ether is attractive due to its cost benefit and ease of handling. Primary alkyl or aromatic diamine are preferred corsslinkers for heat curing of Bisphenol A epoxy resin. The main reason for using diamine includes its availability in liquid form, ease of purification and mild curing temperature. Moreover, the diamine gives sufficient surface to accommodate the PPy strands and polymeric membrane network. Diamine crosslinkers were purified by vacuum distillation over barium oxide or calcium hydride. For the straight chain alkyl diamine the preferred number of methylene units are two to six (n = 0 to 4).

[35] The homogeneous polypyrrole cocktail for solvent casting on electrode 14 surface contains binder material that is cure-able at room temperature or gentle oven treatment. The solution cast polypyrrole gives reproducible cyclic voltammograms and usable as transducer layer 16 for chemical sensors. The solution cast conductive polymers is usable as transducer layer 16 for ion selective electrode 10 chemical sensors.

[36] In one preferred embodiment of the ion selective electrode 10 as illustrated in Figure 1, a circular shaped carbon layer is screen printed on pre-fabricated conductor layer 14 preferably silver. For the preparation of the ion selective electrode 10, the silver layer 14 can be electrochemically deposited or screen printed on the substrate 12. Bisphenol A propoxylate diglycidyl ether-diamine binder is repeatedly screen-printed and oven cured to afford sufficient height to function as retaining dam 20. Solution cast conductive polymer cocktail can be dispensed into the dam 20 and dried under inert atmosphere forming the transducer layer 16. The function of the heat curable retaining dam 20 is to contain the cocktail of sensing membrane 18 without losing the active components via diffusion into the said retaining dam 20.

[37] Likewise, the polymeric sensing membrane 18 and photocurable sensor components can also be dropped coated into the dam 20, followed by UV-curing or drying.

[38] Poplypyrrole is use as example for the solution cast polymer transducer layer 16. Alternatively, other conductive polymer may be used in place of polypyrrole such as polythiophene, polyaniline or combination thereof. Also, the diamine binder may be selected from at least one or combination of m-xylylenediamine, p-xylylenediamine, p - phenylenediamine, 1,3-diaminopropane, 1,4-diaminobutane.

[39] The polar solvent is selected from the list of methanol, ethanol, n-propanol, iso- propanol, tetrahydrofuran, diethylether, dimethylsulfoxide, acetonitrile, acetone, water or combination thereof.

[40] The method of preparation of ion selective electrode 10 is applicable to manufacture a wide range of chemical sensor as described in the following examples.

[41] The invention now being generally described, the same will be better understood by reference to the following detailed examples which are provided for purposes of illustration only and are not to be limiting of the invention unless so specified.

[42] Example 1

[43] Preparation of Screen-Printed Carbon Electrode

[44] Carbon paste is screen printed on conductor layer 14 such as copper-gold or prefabricated screen printed silver. The optimized dry thickness of both screen printed carbon and silver conductor layer 14 are 100 micrometer. The circular shaped conductor layer 14 known as electrodes with 3mm diameter is printed on polyester or printed circuit board substrate 12 and separated by 2mm spacing from each other for integrated multi-sensor application. The printed paste was cured at 120 °C to give the desired dry thickness. Solder mask insulating layer was also screen printed to define the electrode window, separate the wells and protect the printed conducting wires 14.

[45] Example 2

[46] Preparation of Solution Cast Polypyrrole Transducer with

[47] Bisphenol A Propoxylate Diglycidyl Ether-Diamine

[48] Bisphenol A propoxylate diglycidyl ether, doped polypyrrole fine black powder and m-xylylene diamine were procured from Sigma- Aldrich. The Bisphenol resin and doped polypyrrole were used as received. -Xylylene diamine was purified by the following steps: diluting with diethyl ether, washing with saturated sodium bicarbonate and brine solutions, drying with sodium sulfate followed by magnesium sulfate and stirring over barium oxide, phosphorus pentoxide or calcium hydride for 3 to 12 hours followed by distillation under reduced pressure. Bisphenol A diglycidyl resin (100 mg) was transferred into a glass vial and 50 uL of purified m-xylylene diamine crosslinker was added into the resin, and the mixture diluted with ethanol to give 10 weight percent solution of the Bisphenol-m-xylylene binder. The vial was tightly capped and sonicated at 40 °C for 30 minutes. Doped polypyrrole powder (300 mg) and 50 mg sodium ^-toluene sulfonate were added into a glass vial and the mixture was dissolved with ethanol to give 10 weight percent doped polypyrrole solution. The vial was tightly capped and sonicated at 40 °C for 30 minutes. The polypyrrole-salt solution (30 uL) and 20 uL of the Bisphenol-diamine solution and were combined and in a glass vial. The vial was tightly capped and sonicated at 40 °C for 30 minutes. The solvent cast polypyrrole cocktail was stored at 4 °C before use.

[49] Example 3

[50] pH ISE with Solvent Cast Polypyrrole Transducer [51] pH Sensor cocktail was prepared by mixing 37mg poly(vinyl) chloride (PVC), 3mg sodium tetrakis[bis-3,5(trifluoromethyl)phenyl] borate (NaTFPB), 10.6mg tridode- cylamine (Hydrogen Ionophore I), 67mg bis(2-Ethylhexyl) Sebacate (DOS) and 600 uL tetrahydofuran (THF) solvent. The solvent cast polypyrrole solution (5 uL), prepared as described in Example 2, was drop coated onto screen-printed carbon electrode 14 and the solvent evaporated under nitrogen atmosphere for 1 hour. Cyclic voltammetry of the solvent cast polypyrrole was performed with Metrohm Autolab system in 0.1M potassium chloride solution transducer layer 16 with silver-silver chloride double-junction reference electrode and platinum counter electrode. The homogenous pH cocktail for the preparation of the sensing membrane 18 was drop coated on the freshly prepared polypyrrole transducer layer 16 and dried under continuous flow of nitrogen gas for 2 hours or air dried at ambient temperature for 12 hours. This pH sensor was tested using commercial Ag AgCl double junction reference electrode with 0.1M LiOAc as outer solution. The results were shown in Figure 3. The plots of emf response versus activity of hydrogen ion shows acceptable Nernstian response and linearity.

[52] Example 4

[53] Potassium ISE with Solvent Cast Polypyrrole Transducer

[54] Potassium sensor cocktail was prepared by mixing 90mg poly( vinyl) chloride (PVC), 5.4mg potassium tetrakis[para-cholorophenyl] borate (KTpClPhB), 24.3mg

Valinomycin (Potassium Ionophore), 219.9mg bis(2-Ethylhexyl) Sebacate (DOS) an 1800 D L tetrahydofuran (THF) solvent. The solvent cast polypyrrole solution (5 uL ), prepared as described in Example 2, was drop coated onto screen-printed carbon electrode 14 and the solvent evaporated under nitrogen atmosphere for 1 hour. Cyclic voltammetry of the solvent cast polypyrrole was performed with Metrohm Autolab system in 0.1M potassium chloride solution with silver-silver chloride double-junction reference electrode and platinum counter electrode. The potassium cocktail for the preparation of the sensing membrane 18 was drop coated on the freshly prepared polypyrrole transducer layer 16 and dried under continuous flow of nitrogen gas for 2 hours or air dried at ambient temperature for 12 hours. This potassium sensor was tested using commercial Ag/AgCl double junction reference electrode with 0.1M LiOAc as outer solution. The results were shown in Figure 4. The plots of emf response versus activity of potassium ion shows acceptable Nernstian response and linearit

[55] Example 5

[56] Nitrate ISE with Solvent Cast Polypyrrole Transducer

[57] Nitrate sensor cocktail was prepared by mixing 33 mg poly( vinyl) chloride (PVC), 3 mg tetraoctyl ammonium nitrate, 67 mg 2-nitrophenyl octyl ether (NPOE) and 1 mL tetrahydofuran (THF) solvent. The solvent cast polypyrrole solution (5 |JL), prepared as described in Example 2, was drop coated onto screen-printed carbon electrode 14 and the solvent evaporated under nitrogen atmosphere for 1 hour. Cyclic voltammetry of the solvent cast polypyrrole transducer layer 16 was performed with Metrohm Autolab system in 0.1 M potassium chloride solution with silver-silver chloride double- junction reference electrode and platinum counter electrode. The nitrate sensor cocktail for the preparation of the sensing membrane 18 was drop coated on the freshly prepared polypyrrole transducer layer 16 and dried under continuous flow of nitrogen gas for 2 hours or air dried at ambient temperature for 12 hours. This nitrate sensor was tested using commercial Ag/AgCl double junction reference electrode with 2M ammonium sulfate as outer solution. The results were shown in Figure 5. The plots of emf response versus activity of nitrate ion shows acceptable Nernstian response and linearity.

[58] The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are to be regarded as within the scope of the invention, and all such modifications as would be apparent to one skilled in the art are intended to be within the scope of the following claims.

Best Mode

[59]

Mode for Invention

[60]

Industrial Applicability

[61]

Sequence List Text

[62]

Claims

1. Ion selective electrode 10 for electrochemical sensing comprising a substrate 12;

a conductor layer 14;

a solution cast conductive polymer transducer layer 16 to convert chemical concentration to electrical signal;

a sensing membrane 18 having ion recognizing molecule, lipophilic salt and lipophilic organic polymer to selectively detect ionic analyte;

a retaining dam 20 to contain a cocktail of the sensing membrane 18; characterised in that,

the solution cast conductive polymer transducer layer 16 comprises of ; a bisphenol A propoxylate diglycidyl ether, a purified diamine binder; a polymer; an organic sulfonate salt; and a polar solvent.

2. The ion selective electrode 10 according to Claim 1 , characterised in that the solution cast conductive polymer transducer layer 16 wherein the polymer is at least one or combination of polypyrrole, poly- thiophene, polyaniline.

3. The ion selective electrode 10 according to Claim 1, characterised in that the solution cast conductive polymer transducer layer 16 contains 3 to 30 weight percent of Bisphenol A propoxylate diglycidyl ether- diamine binder in polar solvent.

4. The ion selective electrode 10 according to Claim 1, characterised in that the diamine binder is selected from at least one or combination of m-xylylenediamine, p-xylylenediamine, p-phenylenediamine,

1 ,3-diaminopropane, 1 ,4-diaminobutane.

5. The ion selective electrode 10 according to Claim 1, characterised in that the conductor layer 14 is selected from the list of carbon, silver, copper, gold, platinum or combination thereof.

6. The ion selective electrode 10 according to Claim 1 , characterised in that the polar solvent is selected from the list of methanol, ethanol, n - propanol, wo-propanol, tetrahydrofuran, diethylether, dimethyl- sulfoxide, acetonitrile, acetone, water or combination thereof.

7. The ion selective electrode 10 according to Claim 1, characterised in that the retaining dam 20 is screen-printed paste of Bisphenol A propoxylate diglycidyl ether-diamine paste.

8. The ion selective electrode 10 according to Claim 1, characterised in that the solution cast conductive polymer transducer layer 16 comprises 3 to 10 percent polypyrrole, 1 to 5 percent Bisphenol A propoxylate diglycidyl ether, 1 to 5 percent diamine crosslinker and 2 to 5 percent para-toluene sulfonic acid, all by weight, in polar solvent.