GB2102963A

GB2102963A - Film-form ion selective electrode and method of measuring ion activity using the same

Info

Publication number: GB2102963A
Application number: GB08220364A
Authority: GB
Inventors: Shigemitsu Mizutani; Shuzo Fuchigami; Tadashi Kawada; Mineo Suefuji; Kikuo Kubodera; Osamu Seshimoto; Asaji Kondo
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1981-07-13
Filing date: 1982-07-13
Publication date: 1983-02-09
Also published as: JPS5810645A; DE3226045A1; GB2102963B

Abstract

In a film-form ion selective electrode composed essentially of a conductive layer 2 and an ion selective layer 5 for measuring ion concentration or ion activity of an aqueous liquid such as body fluids, at least the edge portions of the conductive layer being covered with the ion selective layer to prevent the occurrence of short circuits in the electrode. <IMAGE>

Description

SPECIFICATION Film-form ion selective electrode and method of measuring ion activity using the same This invention relates to an electrode for measuring ion concentration or ion activity, and more particularly to a film-form ion selective electrode (hereafter referred to as an ion selective electrode film) for potentiometrically measuring the ion concentration of body fluids such as an aqueous liquid, blood, serum, etc. and an ion electrode assembly for measuring ion concentration using the ion selective electrode.

This invention further relates to an ion selective electrode film which does not cause electric short circuiting accidentally occurring from an overflow of a sample liquid at measurement and hence does not require anti-shorting means, an ion selective electrode assembly using the ion selective electrode film, and a method of measuring ion concentration or ion activity using the foregoing electrode assembly.

The term "electrode" as used herein refers to a so-called half cell or monopole.

In general, the measurement of the concentration of inorganic ions such as K+, Na+, Cl-, HCO3-, etc., in body fluids is important in the clinical field and wet procedures using ion selective electrodes have already been used in the art for this purpose.

These known methods are of the type that an ion concentration is measured by dipping a needle electrode in a liquid. It is troublesome to control the electrode from viewpoints of maintenance, washing, conditioning, life, damage, etc., and it is necessary to use more than several hundred ,ul of a sample liquid since the electrode head must be sufficiently dipped in the sample liquid placed in a cup each time.To eliminate such inconveniences, an electrode film of such a type that a sample liquid is spotted or dropped on a dry electrode film is disclosed in Japanese Patent Application (OPI) 142584/77 (the term "OPI" as used herein refers to a patent application which has not yet been examined but open to public inspection), and also a method of using a fine wire-form dry-operative ion selective electrode is disclosed in Japanese Patent publication 47717/77 and Japanese Patent Application (OPI) 128793/74.The ion selective electrode film disclosed in Japanese Patent Application (OPI) 142584/77 is a dry-operative electrode formed by coating on a metal layer, a layer of a water-insoluble salt of the same metal as that of the metal layer, a dried electrolyte layer composed of a hydrophilic binder matrix containing having dissolved therein a water-soluble salt having the same anion as that of the foregoing water-insoluble salt, and an ion selective membrane layer on an insulating film in this order. Two of these electrode films are connected together by a bridge to form a pair of electrodes. After connecting the electrodes to a potentiometer, a sample liquid and a control liquid are dropped onto a pair of electrodes, respectively, and the potential difference is measured, whereby the concentration of the sample liquid can be determined.

Further, Japanese Patent Application (OPI) 128793/74 discloses a method wherein a solid state ion selective electrode formed by coating concentrically a metallic wire with a layer of a waterinsoluble salt of a metal same as that of the metal wire, an electrolyte layer containing the same anion as that of the water-insoluble salt, and an ion selective membrane layer in this order is connected to a potentiometer together with a saturated calomel electrode (as a reference electrode) and by dipping the electrode in a sample liquid, the potential difference is measured. In these dry ion selective electrodes, a specified ion can be measured by changing the kind of the ion selective membrane as the uppermost layer and hence there are many kinds of electrodes each for measuring, e.g., K+, Na+, Cl-, HCO3-, etc.

However, these dry type ion selective electrode film encounter, at the practical use, the following difficulties.

That is, when a sample liquid and a control liquid are dropped onto the foregoing electrode films, respectively, each drop of the sample liquid tends to spread over the surface of the ion selective membrane (or a protective layer when the protective layer is formed on the ion selective membrane layer) or each electrode film. The spread liquid flows down over the edge portion of the electrode film to short various layers constructing the electrode, which results in generating incorrect potential or providing zero potential to give incorrect value of the potentiometer. Consequently, it is necessary for such a kind of ion selective electrode film to avoid the occurrence of such a short circuit by the sample liquid or control liquid.

Japanese Patent Application (OPI) 142584/77 proposes a method of preventing the occurrence of shorting of the constructing layers of an electrode film by forming a plastic platform or an adhesive strip for protecting with a water-impermeable and electric insulating film in such a manner that the ion selective layer only of the electrode film is exposed and other portions of the electrode film are not permeated with water or an aqueous liquid. However, in such a method, much labor is required since the aforesaid processing must be applied to each electrode film as well as it is difficult to completely avoid the occurrence of shorting since the processing is a troublesome work.

U.S. Patent 4,053,381 describes an ion selective electrode film composed of a pair of conductive metal members having formed thereon in common three layers, i.e., a water-insoluble salt layer, an electrolyte layer, and an ion selective layer. However, since the ion activity measuring device disclosed in the foregoing U.S. Patent has the structure that an electrode film composed of the layers having functions as an electrode, each having an exposed edge, is fixed to a frame, a specific frame must be used so that a dropped sample liquid does not spread from the dropped place to an undesirable place for preventing sample liquids from being brought into contact with each other to cause shorting or preventing a sample liquid itself from flowing down over the edge of the electrode film to short the constructing layers of the electrode.

Summary of the invention As a result of various investigations on attempting to eliminate the foregoing disadvantages in the conventional techniques, the inventors have discovered that the employment of a specific antishorting means becomes unnecessary by covering the conductive layer with the ion selective layer and have succeeded in attaining this invention based on this discovery.

An object of this invention is to provide a dry type ion selective electrode film without need of a complicated anti-shorting design which is necessary in conventional electrode films.

A further object of this invention is to provide an ion selective electrode assembly capable of determining plural items and also to provide a method of measuring ion concentration without need of a specific anti-shorting design using the ion selective electrode assembly.

Thus, according to this invention, there is provided a dry type film-form ion selective electrode comprising a conductive layer composed of a conductive metal or a conductive metal oxide and an ion selective layer coated in this order, the edge surface of the conductive layer being covered with the ion selective layer. The ion selective electrode may have a support, if desired and necessary.

This invention also provides an ion selective electrode assembly for measuring ion concentration or ion activity comprising a pair of the foregoing ion selective electrode films or three or more of the foregoing ion selective electrode films disposed on a common support having an insulating surface.

This invention further provides a method for measuring ion concentration or ion activity by applying a sample liquid and a control liquid onto the ion selective layer of the foregoing ion selective electrode film to perform the measurement while preventing the sample liquid from being directly brought into contact with the conductive layer to avoid the occurrence of shorting.

Brief description of the drawings Figure 1 is a plane view showing the embodiment of Example 2.

Figure 2 is a fragmentary plane view showing a pair of ion selective electrode films cut at 100 in Figure 1.

Figure 3 is a fragmentary plane view showing a pair of ion selective electrode films cut at 200 in Figure 1.

Figure 4 is a fragmentary plane view showing ion selective electrode films for measuring two items cut at 300 in Figure 1.

Figure 5 is a schematic sectional view showing the case of measuring ion concentration using the ion selective electrode film shown in Figure 2.

Figure 6 is a schematic plane view of the embodiment shown in Example 3 showing an example of electric connection in the case of measuring ion concentrations of two items by changing over a switch.

Figure 7 is a fragmentary plane view showing the embodiment of Example 4.

Figure 8(A) shows an example of electrical connections in the case of measuring plural items by changing over interlocked switches Sw, and Sw2 and (B) shows an example of a measuring plural items by feeding successively the electrode film to the potentiometer.

Figure 9 is a plane view of the embodiment of Example 5.

Figure 10 is a plane view showing a pair of ion selective electrodes cut at 400 in Figure 9.

Figure 11 is a side view showing the embodiment of the ion selective electrode film assembly in Example 13, wherein Figure 11 A is a side view showing the ion selective electrode films, Figure 11 B is a side view showing a spacer, Figure 11 C is a side view showing a bridge member, and Figure liD is a side view showing an upper support, the foregoing members being assembled in this order.

Figure 11 is a side view showing the external appearance of the ion selective electrode film assembly in Example 1 3.

Figure 13 is a plane view showing a fundamental example of electric connection in the case of measuring a potential using an assembly having the same construction as that of the ion selective electrode film assembly shown in Example 13.

Figure 14 is a schematic plane view showing an ion selective electrode film cut as one film unit in the embodiment shown in Example 14.

Figure 1 5 to Figure 19 are schematic sectional views showing various embodiments of the ion selective electrode films of this invention.

Figure 20 is a schematic plane view showing a mask used for the vapor depositing of patterns of a silver layer and a silver chloride layer on a PET film support in the step of forming the ion selective electrode film couples by the embodiment shown in Example 1.

Figure 21 is a schematic view showing the case of measuring a potential by the method shown in Example 1 using the ion selective electrode film shown in Example 1.

Description of the preferred embodiment The term "covering" as used herein can be any embodiment as far as electric contact to a lead wire or a probe of a potential measuring device in a conductive layer is ensured and includes a case of covering a part of the conductive layer as well as a case of covering the whole of the conductive layer.

In this invention, it is preferred that the ion selective layer has an electrically insulating property in a dry state before it is brought into contact with a sample liquid or a control liquid but an ion selective layer having an electric conductivity lower than that of a semi-conductor in a dry state can be practically used in this invention.

The ion selective electrode film of this invention may further include, in addition to the foregoing fundamental constructional layers, functional layers imparting various functions in response to purposes and uses, function assisting layers for assisting various functions, and/or a structure assisting layer for assisting the structure itself. Therefore, the ion selective electrode of this invention may have, for example, the following structures: (1) An ion selective electrode film composed of, if desired and/or necessary, a support, a conductive metal layer, a layer of a water-insoluble salt of the metal same as the metal of the conductive metal layer, and an ion selective layer, which are laminated in succession.

(2) An ion selective electrode film having further an electrolyte layer formed between the waterinsoluble metal layer and the ion selective layer of the foregoing ion selective electrode film (1).

(3) An ion selective electrode film having a protective layer in place of the ion selective layer of the foregoing ion selective electrode film (1).

(4) The ion selective electrode films (1), (2) and (3) described above, each having further an adhesive layer between proper layers of them.

The term "laminate", "laminating" or "laminated" as used herein refers to a state of forming into layers depending upon techniques conventionally used in the art: for example, a conductive metal layer is provided generally by means of a deposition technique and other layers are generally formed by means of a coating technique, unless otherwise indicated.

In addition, as a matter of course, ion selective electrode films other than the foregoing examples having the structures well known in the art are also included in the scope of this invention.

The ion selective electrode film of this invention does not require anti-shorting means and hence the edge surface of the conductive layer is covered by the ion selective layer as the feature of this invention. The covering procedure is performed usually in the state of partially exposing the conductive layer for ensuring the electric contact state in the conductive layer. However, the conductive layer may, as a matter of course, be wholly covered by the ion selective layer if the electric connection with the conductive layer is ensured.

When the form of the film-form electrode is a quadrilateral form, covering by the ion selective layer is generally performed in the following manner: (A) The conductive layer is covered by the ion selective layer continuously from the surface of the three edge surfaces except one edge portion of the conductive layer to which a lead wire is connected.

(B) The conductive layer is covered by the ion selective layer at the two edge surfaces including the edge surface to which a bridge is applied among the foregoing three edge portions excluding the portion of the conductive layer to be connected to a lead wire.

(C) The conductive layer is covered by the ion selective layer at the edge surface, to which a bridge is applied, from the surface of the conductive layer.

(D) The whole edge surfaces of the ion selective electrode film are covered by the ion selective layer continuously from the surface of the conductive layer.

In general, a part of the edges of the conductive layer or a part of the surface of the edges of the conductive layer may be exposed or uncovered without being covered by the ion selective layer over the area capable of functioning as a terminal for electric connection, and thus a structure that a part of the edges of the conductive layer or a part of the surface of the conductive layer is exposed without being covered by the ion selective layer can be employed in this invention, regardless of the form of the ion selective electrode film, such as a quadrilaterai, a circle, an oval, a polygon, and a partial combination of these.

From the viewpoint that an anti-shorting means is unnecessary, it is clear that the following structure may be employed in this invention; that is, the structure of covering at least the edge of the conductive layer with the ion selective layer at the portion where a sample liquid or a control liquid spotted or dropped on the ion selective layer or reached the ion selective layer of the portion that the functional layers (a layer of a water-insoluble salt of the conductive metal, an electrolyte layer, an ion selective layer, and a conductive layer except the terminal portion for electric connection) of the ion selective electrode film.

Examples of typical layer structures of the ion selective electrodes of this invention in the case of applying thereto "covering" in this invention are models as shown in Figure 1 5 to Figure 1 9 as sectional views thereof. In the figures, numerals mean, 1: PET support, 2: silver layer or a conductive metal (silver) layer, 3: silver chloride layer, 4: electrolyte layer and 5: ion selective layer.

Figure 15A shows an ion selective electrode film having a layer structure composed of a support 1, a layer 2 of a conductive metal silver, and an ion selective layer 5 corresponding to the foregoing covering mode (C). The edge surface which is most easily permitted to bring into contact with a down flowing liquid at the four edge surfaces of the electrode film is the edge surface to which a bridge is applied but since the edge surface is previously covered by the ion selective layer 5 as shown in Figure 15A, the occurrence of an incorrect potential caused by shorting can be completely prevented in this invention. In this invention, an appropriate functional layer or layers may be formed between the conductive metal layer 2 and the ion selective layer 5.For example, when a layer 3 of a water-insoluble salt of the conductive metal is formed, the covering mode as shown in Figure 1 5D or Figure 1 5E may be employed. In any covering modes, the edge surface of the conductive metal layer is covered by the ion selective layer and hence the covering mode in this invention includes both the direct covering mode and the indirect covering mode by the ion selective layer.

Figure 1 6 corresponds to the foregoing covering mode (D). When the whole surface of the conductive layer is covered by the ion selective layer as shown in the figure, the electric connection with the conductive layer is secured by piercing a needle-lilce electric connection terminal (probe) into the conductive metal layer 2 through the ion selective layer 5 or the support 1. Such a method is already known in the field of the art and is reported in detail, in, for example, Research Disclosure, No.

15767, May 1977.

When two dry type ion selective electrode films of this invention are used as a pair of electrodes at measuring the concentration or activity of an electrolyte, it is preferred to prepare the pair electrode films in the form that a common ion selective layer is applied on a pair of conductive layers. Typical examples of this embodiment are shown in Figure 17 to Figure 1 9.

As described above, in this invention, by directly or indirectly covering an edge portion of the conductive layer with the ion selective layer while ensuring the electric connection with the conductive layer, no shorting by a sample liquid or a control liquid occurs.

As the materials constructing the dry type ion selective electrodes of this invention, the materials used for known electrodes in the field of the art can be used.

First, as the conductive metal for the ion selective electrodes of this invention, the conductive metals used for known electrodes disclosed in the patents supra can be used. Preferred examples of the conductive metals used in this invention are silver, platinum, palladium, gold, nickel, copper, aluminum, indium, etc. Further, the conductive metal oxides used in this invention are described in, for example, Per Kofstad, Nonstoichiornetry, Diffusion and Electrical Conductivity in Binary Metal Oxides, New York, Woley Interscience (1 972), etc.Practical examples of the conductive metal oxides are tin oxide (SnO2), indium oxide (In203), zinc oxide (ZnO), iridium oxide (IrO2), cadmium oxide (CdO), thallium oxide (Tl203), iron oxide (Fe304), lead oxide (pub02 or PbO), vanadium oxide (V203 or VO), bismuth oxide (Bi2O3), berillium oxide (BeO), manganese oxide (MnO2), molybdenum oxide (MoO2), a mixture of tin oxide and antimony oxide, and a mixture of tin oxide and indium oxide. Preferred examples of the conductive metal oxides are tin oxide, indium oxide, zinc oxide, a mixture of tin oxide and antimony oxide, and a mixture of tin oxide and indium oxide.

The conductive metal can be used as a foil, a film, or a metal thin layer formed on an appropriate support such as a glass sheet, a ceramic plate, a polymer sheet or film, a paper, etc. The conductive metal oxide having high self-supporting property and high mechanical strength may be used as the same form as that of the conductive metal as described above but the conductive metal oxide having weak self-supporting property and weak mechanical strength may be used as a thin metal oxide layer formed on a support such as a glass sheet, a ceramic plate, a polymer sheet or film, or paper.

The thin layer of the conductive metal or the conductive metal oxide can be formed by applying a known method. That is, there are, for example, a method of vapor depositing silver, a method of performing chemical plating, a method of forming a metal silver layer containing, for example, gelatin by forming a silver halide-hydrophilic colloid emulsion layer as used for silver halide photographic material followed by overall or imagewise exposure and development, and a method of forming a conductive metal layer or a conductive metal powder or a conductive metal oxide powder in a binder on a support using a known method such as coating, etc., followed by drying by removing the solvent used for solidification of the binder by polymerizing and polycondensing the binder.

In the case of using a binder, it is preferred to use a hydrophobic binder the same as or similar to the binder for an ion selective layer which will be formed afterwards.

The binder and solvent used in these cases can be selected from known materials. For example, the binder may be selected from binders used for the foregoing dry type electrodes and binders and adhesives for coating. Examples of these binders are gelatin, polyacrylamide, polyvinyl alcohol, alcoholsoluble polyamide, cellulose diacetate, cellulose triacetate, polyvinyl chloride, chlorinated polyethylene, chlorinated polypropylene, polystyrene, etc.

In one embodiment of this invention, the conductive layer is laminated on a support and for large scale or mass production, it is convenient to form the conductive layer on a support in a stripe like or pattern like manner suited for the purpose and use.

When the conductive layer is used as a foil, a film, or a thin layer on a support, it is desirable that the thickness is generally from about 50 nm to about 50,us.

In a preferred embodiment of this invention, the ion selective electrode has a support. The support can support other portion of the electrode directly or through a proper function-assisting layer or structure-assisting layer and the support can be selected from broadly known materials having electrically insulating property and electrically inert property. Preferred examples for the support are cellulose acetate, polyethylene terephthalate (PET), polycarbonates such as Bisphenol A polystyrene, etc. It is preferred that the thickness of support be generally from 0.05 mm to about 0.5 mm.

The support is not always necessary in this invention and when the conductive layer and/or the ion selective layer has a sufficient mechanical strength as the electrode itself or for supporting other necessary portions, it is unnecessary to form a support.

A layer of a water-insoluble salt, which is formed on the conductive metal layer, can be formed by a known method. That is, the layer may be formed by a method of vapor-depositing a metal salt, a method of treating a metal layer with an aqueous K2Cr2O7. HX solution or an aqueous K3[Fe(CN)6]NaOHKX solution is most excellent in view of stability. The thickness of the layer of the insoluble salt is generally 50 Fum to 10 jum.

When the conductive metal layer is a silver layer, a part of the surface thereof is left in a metallic silver state without being converted into silver halide for a part of the silver layer as a terminal for electric connection. For the purpose, a method of masking the portion by coating the portion with a resist, a method of masking the portion by coating a resist which can be removed by alkali as disclosed in Research Disclosure, No. 19445, June 1980, a method of masking the portion by forming thereon a thin vapor deposited layer 6r nickel of chromium having a thickness of 5 nm to 20 nm as disclosed in Japanese Patent Application (OPI) 33537/81 (corresponding to U.S.Patent 4,259,164), or a method of masking the portion by forming thereon a thin vapor deposited layer of palladium having a thickness of 1.5 nm to 1 5 nm or a thin vapor deposited layer of indium having a thickness of 3 nm to 20 nm may be applied.

The electrolyte layer, which is formed on the layer of a water-insoluble salt, may be formed by a known method. For forming the electrolyte layer, the techniques described in Japanese Patent Application (OPI) 142584/77 (corresponding to U.S. Patents 4,053,381,4,11,246 and 4,214,968) and Japanese Patent Application No. 92379/80 (corresponding to (OPI) 17852/82) can be employed.

The ion selective layer is a layer which can select a specific ion and has, preferabiy, an electrically insulating property in the dry state prior to contact with a sample liquid or a control liquid. The term "layer can select a specific ion" includes not only the case of selectively permeating a specific ion only or responding to a specific ion only but also the case where a specific ion can be selected from other unnecessary materials with a sufficient time difference for the measurement. Further, the case where a potentiometrical response corresponding to the change of ionic activity in a liquid is measured by ion exchange, whereby the same function as the function of selecting a specific ion is obtained is included in the term "layer can select a specific ion" in this invention.

Since a sample liquid and a control liquid, which, as the case may be, are both aqueous liquids, the ion selective layer of the ion selective electrode of this invention must be water-insoluble. The ion selective layer may be hydrophilic or hydrophobic if it is insoluble in water, but it is preferred that the ion selective layer be hydrophobic.

As will be stated later, the ion selective layer is, in many cases, composed of an ion carrier, an ion carrier solvent, and an organic binder (or a matrix composed of an organic binder) and hence the property of the ion selective layer for water mainly depends upon the property of the organic binder for water. Therefore, for obtaining a hydrophobic ion selective layer, a hydrophobic organic binder may be used.

A most typical ion selective layer is composed of an ion carrier, an ion selective layer is composed of an ion carrier, an ion carrier solvent, and a hydrophobic organic binder (or a matrix of a hydrophobic organic binder). As the ion carrier, there are valinomycin, cyclic polyether, tetralactone, macrolide actin, enniatins, monensins, gramicidins, nonactins, tetraphenyl borate, cyclic polypeptide, etc.

As the ion carrier solvent, there are bromophenyl phenyl ether, -3-methoxyphenyl phenyl ether, 4- methoxyphenyl phenyl ether, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, dioctylphenyl phosphate, bis(2-ethylhexyl) phthalate, octyldiphenyl phosphate, tritolyl phosphate, dibutyl sebacate, etc.

As the hydrophobic organic binder, there are hydrophobic natural or synthetic polymers capable of forming thin film, such as, for example, cellulose ester, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyurethane, polycarbonate, vinyl chloride-vinyl acetate copolymer, etc.

For the ion carriers, ion carrier solvents, hydrophobic organic binders, and the ion selective layers composed of these materials, the materials and techniques described in Japanese Patent Application (OPI) 142584/77, U.S. Patents 4,053,381, 4,171,246 and 4,214,968, and Research Disclosure, No.

16113, September 1977 can be used.

lon exchange resins can also be used as the materials for the ion selective layers. In the case of using an ion exchange resin, a potentiometric response occurring due to the change of ionic activity in an ion-containing solution is measured.

The ion exchange resin used in this invention may be cationic or anionic. As the proper ion exchange resins used in this invention, there are quaternary alkyl, aryl or aralkyl ammoniums, phosphoniums, arsoniums, stiboniums, or sulfoniums; dialkyldithiocarbamates; dithiophosphates: aryls; arsenates; p-diketones; toluene-3,4-dithiol; glyxoal bis(2-hydroxyanil); phenanthrolines; polypyridyls: tetraalkylmethylene diphosphonates; long chain alkyl or aralkyl mercaptans; oximes; 8mercaptoquinoline; metal chelates of these substituents; sulfonated polystyrene, etc. Details of these materials and the formation of the ion selective layers using them are described in Japanese Patent Publication 47717/77 (corresponding to U.S. Patent 4,11 5,209).

The ion selective layer is inevitable when the ion to be measured is K+, Na+, Ca++ or HCO3 but the ion selective layer is unnecessary when the ion to be measured is Cl-, the electrode is a metal layer composed of silver, and the layer of the water-insoluble metal salt is composed of silver chloride. In the latter case, in place of the ion selective layer, a layer composed of the material described in Japanese Patent Application (OPI) 89741/80 (corresponding to U.S. Patent 4,199,412), such as cellulose esters (e.g., cellulose acetate butyrate, cellulose acetate propionate, hydrolyzed cellulose acetate butyrate, and the mixed ester thereof) or the latex described in Japanese Patent Applications (OPI) 72622/78 and 1384/79 is formed as a protective layer having a permeability for the ion being detected.

The ion selective layer, which is formed on the conductive metal layer or conductive metal oxide layer, can be formed by a known method. For example, an ion carrier is dissolved in a solvent and after adding the solution to a binder solution, the mixture is coated and dried. The concentration of the ion carrier is generally 0.05 g/m2 to 10 g/m2 and the thickness of the ion selective layer is about 3 to about 1 25 um, preferably 5 to SO um.

As the electrolyte layer used for constituting the ion selective electrode of this invention, materials used for the known such electrodes can be used. The details of the electrolyte layers employed in this invention are described in U.S. Patent 4,214,968, Japanese Patent Application (OPI) 142584/77, U.S. Patents 4,053,381 and 4,171,246, and Japanese Patent Application 92379/80 (corresponding to (OPI) 17852/82).

The electrolyte layer is formed on the foregoing water-insoluble metal salt layer by a vacuum deposition method or by coating thereon an aqueous solution of an electrolyte followed by drying.

Preferred results are obtained by a vacuum deposition method. The vacuum deposition is generally performed in vacuo of 10-4 to 10-7 Torr. The thickness of the electrolyte layer is generally 0.1 to 2.5 g/m2.

The ion selective electrode film of this invention does not cause shorting between the layers thereof by a sample liquid or a control liquid due to the structure of the electrode itself as compared with the ion selective electrode having a conductive metal layer, an insoluble metal salt layer, and an electrolyte layer composed of a binder and an electrolyte as disclosed in Japanese Patent Application (OPI) 142584/77 and hence the ion selective electrode of this invention does not require any antishorting means and also has very good stability. By the ion selective electrode of this invention, an ion concentration or ion activity can be determined correctly and with good reproducibility so that it can be suitably used for an analysis requiring high accuracy.

The ion selective electrode film of this invention is suitable for use as the ion selective electrode assembly as described in Japanese Utility Model Application (OPI) 64759/80 (corresponding to U.S.

Patent 4,250,010). That is, at least a pair of electrodes composed of two ion selective electrode films of this invention are disposed on a support having an insulating surface so that they are adjacent to each other with an interval for not shorting the terminal portions of the electrodes with each other to form an ion selective electrode assembly. In this case, when the ion selective electrodes capable of selecting at least two different kinds of ions are used, by spotting or dropping once a sample liquid containing plural different ions onto the central portion of the electrodes disposed on the support, ion concentrations for plural items can be determined.

Further, as described above, the conductive layer can achieve the object thereof if the portion of causing a surface potential and the portion of ensuring electric connection are secured, and hence terminal patterns for electric connection as shown in, for example, Figure 11 A may be formed by the vapor deposition of a conductive metal, whereby excess expense can be saved.

For performing a potentiometry using the ion selective electrode film of this invention, a so called absolute method or differential method can be employed. In the absolute method, the electrodes include one ion selective electrode film of this invention and one external reference electrode and the potential difference between the ion selective electrode and the reference electrode occurred at spotting or dropping a sample liquid onto the ion selective electrode film is measured. In the differential method, a pair of electrodes composed of two ion selective electrode films of this invention are used and the potential difference occurring when a sample liquid is spotted or dropped to one electrode and a control liquid is spotted or dropped onto another electrode is measured.

The ion selective electrode films of this invention will now be explained in detail by the following examples.

Example 1 In a tungsten basket (a vessel for vapor evaporation source), 4 g of silver having purity of 99.9% was placed and the basket was placed in a vacuum vapor deposition apparatus together with a polyethylene terephthalate film (15 cmxl 2 cm) at definite positions. A masking pattern having many rectangular openings 32 (7 mmx O mm) as shown in Figure 20 was superimposed on the PET film and after evacuating the apparatus to a pressure of 5x 10-5 Torr, silver was vapor deposited on the film until the vapor deposited amount monitor equipped in the apparatus indicated the amount of 7 g/m2.

Then, 3 g of silver chloride having purity of 99.5% was placed in a tungsten basket in the apparatus and after evacuating the apparatus to a pressure of 5x 10-5 Torr, silver chloride was vapor deposited on the vapor deposited silver layer until the monitor indicated the deposit amount of 2.5 g/m2 while maintaining the foregoing masking pattern at the same position. In this case, each opening of the mask was a rectangular opening of 7 mmx 10 mm area so that the vapor deposited pattern thus obtained was composed of rectangular double layers arranged in two lines each composed of a silver layer and a silver chloride layer and having an area of 7 mmx 10 mm.

Then, for covering the whole surfaces of the four edges of each silver layer of the vapor deposited pattern and also the uncovered surface of the PET film with a potassium ion selective layer, a coating solution for the potassium ion selective layer having the following composition was coated on the surface of the film including the silver chloride layers at a width of 35 mm and a dry thickness of 40 ym and dried to form a series of potassium ion selective electrode film pairs.

The potassium ion selective electrode film thus formed had the structure shown in Figure 1 8B or Figure 1 8D as a schematic sectional view.

Composition of potassium ion selective layer coating solution Polyvinyl chloride (mean 2.0 g polymerization degree 800) Dioctyl phthalate 5.0 g Valinomycin 40 mg Tetrahydrofuran 22.5 g Then, the potassium ion selective electrode film pairs were cut into a size of 9 mmx29 mm to provide an electrode film pair chip.

Then, a cotton thread was placed and fixed on the potassium ion selective electrode film pair chip as shown in Figure 21 in which Br indicated a bridge made of a cotton thread. Needle-like terminals (probes) for electric connection were pierced into the electrode films through the ion selective layer until the pointed ends reached the silver layers and after electrically connecting the probes to a potentiometer (input impedance of Sx 1011 ohm, Digital pH Meter HM-1 5A, made byToa Denpa Kogyo K.K.), each of a control liquid containing 1 meq/liter of K+ ion and a sample liquid having a known concentration of K+ ion in a range of from 0.1 meq/liter to 10 meq/liter was spotted or dropped onto each of the electrode films.Thus, when the electromotive force of the potentiometer was measured in each case, a semilogarithmic linear relation to potassium ion was observed. The inclination of the potential line to the potassium ion concentration (logarithmic) was 56 mV per one figure of the potassium ion concentration. The time required from the application of a sample liquid to the final value of a potential (equilibrium potential) was within one minute.

(1) Composition of coating solution for potassium ion selective layer ISLK (5-K) Polyvinyl chloride (mean polymerization degree, 800) 2.0 g Dioctyl phthalate 5.0 g Valinomycin 40 mg Tetrahydrofuran 22.5 g Layer thickness after drying 40 Mm (2) Composition for sodium ion selective layer ISLNa (5-Na) The sodium ion selective layer was prepared by the method described in Example 52 of U.S.

Patent 4,214,968.

Polyvinyl chloride (mean polymerization degree, 800) 40 g/m2 Methylmonencin 1 g/m2 Tris(3-phenoxyphenyl) phosphate 80 g/m2 Tetrahydrofuran was used as the solvent for the coating solution. The layer thickness after drying was 121 g/m2.

(3) Composition for chlorine ion selective layer ISLCI (5-CI) The chlorine ion selective layer was prepared by the method described in Example 50 of U.S.

Patent 4,214,968.

Polyvinyl chloride (mean polymerization degree, 800) 10 g/m2 Didodecyldimethyl ammonium chloride 1 5 g/m2 Didodecyl phthalate 0.25 g/m2 Trioctylpropyl ammonium chloride 0.25 g/m2 Tetrahydrofuran was used as the solvent for the coating solution. The layer thickness after drying was 25.5 gum2.

(4) Composition for carbonic acid ion selective layer lSLHCO3 (5-HCO3) The carbonic acid ion selective layer was prepared by the method described in Example 49 of U.S. Patent 4,214,968.

Polyvinyl chloride (mean polymerization degree, 800) 10 g/m2 4'-Octyl-2,2,2-trifluoroacetophenone 5 g/m2 Further, 60 minutes after the application of the liquid, no change was observed on the equilibrium potential, which indicated that the potential was very stable.

Example 2 On a PET film (13 cmx 15 cm) of 100,um thick was vapor deposited a silver layer 2 in a pattern as shown in Figure 1 under the same conditions as in Example 1. After sticking adhesive polyvinyl chloride tapes having widths of a and 2a (a=5 mm), respectively, on the silver layer 2 thus formed at the positions as indicated in Figure 1, the whole sheet was treated with an aqueous solutipn composed of 5 g of 36% hydrochloric acid, 7 g of potassium dichro- mate, and one liter of water for 6 secs. at 350C to convert the silver of the exposed silver layers into silver chloride 3 (hereafter, the foregoing treatment is referred to as "silver chloride forming treatment").Then, each of 4 kinds of coating solutions having the following compositions for ion selective layers 5 was coated on the silver chloride layers 3 in a stripe form (4 kinds are referred to as 5-K, 5-Na, 5-CI and 5-HCO3) and dried to provide 4 kinds of ion selective electrode films (for K+, Na+, Cl and HCO3-).

Didodecyl phthalate 10 g/m2 Trioctylpropyl ammonium chloride 0.5 g/m2 Tetrahydrofuran was used as the solvent for the coating solution. The layer thickness after drying was 25.5 g/m2.

Then, after peeling off the adhesive tapes from the sheet, the sheet was cut as shown by numerals 100 and 200 in Figure 1, the cut piece at numeral 100 being shown in Figure 2 and the cut piece at numeral 200 being shown in Figure 3, to provide 4 kinds of ion selective electrode film pair chips.

The electrodes of each electrode film pair chips were connected by a bridge Br composed of a cotton thread as shown in Figure 5 (example of using the electrode film shown in Figure 2), and after connecting the edge portion of each silver layer of the electrode film to a potentiometer (Digital pH Meter HM-1 5A, made by Toa Denpa Kogyo K.K.), each of administered sera ("Versatol", (R. T. M.), tradename, made by General Diagnostics Co., Ltd. being used as a control liquid S1 and "Versatol A", made by the same company as a sample liquid S2) was spotted or dropped onto each electrode film and after 3 minutes, the potential difference of the potentiometer was measured. By converting the measured potential differences into concentrations, the concentrations of the electrolytes in Versatol A were measured. The results obtained are shown in Table 1.

Table 1 Concn. of electrolyte (m mol/l) Electrode Measured Measured Verification film ion value value 1-1 K+ ion 7.1 7.2 11-1 Na+ ion 124.5 125 111-1 Cl+ ion 90.5 91 As is clear from the results in Table 1, the measured values coincided well with the verification values.

In addition, when an aqueous solution containing HCO3- was applied to the ion selective electrode film, the electrode showed 27 mV per one figure of the concentration of HCO3 ion.

Example 3 The circuit for measuring two items using the electrode film pair chip for two items (the chip obtained by cutting the sheet along numeral 300 in Figure 1) shown in Figure 4 prepared in Example 2 is shown in Figure 6.

A lead wire from the two electrode films were connected to a potentiometer V as shown in Figure 6.

Then, a bridge composed of a thread or a porous material was placed on the electrode films for connecting the ion selective layers with each other. Each of the sera ("Versatol" being S1 and "Versatol A" being S2) was spotted onto the ion selective layer of each electrode film and after 3 minutes, the potential difference was measured per the first electrode film (K-3).

Then, an electric switch Sw was changed over and then the potential difference of the second electrode film (Na-3) was measured. By converting the measured potential difference into the concentration of each ion, the concentrations of electrolytes in Versatol A were measured. The results thus obtained are shown in Table 2.

Table 2 Concn. of electrolyte (mmol/l) Electrode Measured Measured Verification film ion value value K-3 K+ion 7.2 7.2 Na-3 Na+ ion 124.7 125 As is clear from the results shown in Table 2, the measured value coincided well with the verification values by the simple measurement by the change over of the switch.

As described above, by the use of an electrode film assembly prepared by forming ion selective layers selecting specific ions to be measured in a stripe form as shown in Figure 1 and cutting the portions corresponding to necessary items, potentials for three items or four items can be measured in a simple operation of changing over a switch.

Example 4 By following the same procedures as in Example 2 except that silver layers 2 were formed by vacuum vapor deposition in stripe forms as shown in Figure 7, ion selective electrode film pairs for 4 items measurement (they are referred to as K-4, Na-4, CI-4 and HCO3-4) were prepared.

When the electrode film pairs were connected as shown in Figure 8 and the electrochemical response were measured, results on K+, Na+ and CI coincided well with the verification values as in Example 2 and also almost the same results as in Example 2 were obtained per HCO3-.

In addition the electrode film shown in this example had the structure that the edge surface of the electrode over which the sample liquid or control liquid was spotted or dropped near the bridge and might have spread too much and overflowed was covered by the ion selective layer.

Example 5 Following the same procedure as in Example 2 except that 4 kinds of coating solutions for ion selective layer (5-K, 5-Na, 5-CI and 5-HCO3 in Figure 9) were directly and simultaneously coated on the silver layers 2 vacuum vapor deposited in a stripe form as shown in Figure 9 on a PET film of 1 80 jum thick under the same conditions as in Example 1 and on the uncovered surface of the PET film so that the edges of the silver layers were covered by the ion selective layers followed by drying, ion selective electrode films for measuring 4 items were prepared, By cutting the sheet in the form shown by numeral 400 in Figure 9, an ion selective electrode film pair assembly for measuring 4 items as shown in Figure 10 was obtained.According to the fundamental method shown in Figure 5 using the electrode film pair assembly, each potential difference was measured. In addition, the bridge was removed at each electrode.

In the measurement of 4 items, the measured value of each of the ion concentrations coincided well with the verification value as in Example 2.

Example 6 Following the same procedure as in Example 2 except that the whole surface of a PET film of 100 jum thick was substantially vapor deposited with silver under the same conditions as in Example 1 (without using pattern mask) to form a PET film having a silver deposited layer (vapor deposition amount was 7 g/m2), rectangular stripes of 8 mmx30 mm size were cut from the PET film, and they were fixed on a polystyrene plate of 0.5 mm thick in the pattern as shown in Figure 1, an ion selective electrode film was prepared by applying a silver chloride-forming treatment and subsequent treatments.

When the electrochemical response was measured on each ion of K+, Na+, CI and HCO3 using the electrode film thus obtained, the same results as in Example 2 were obtained.

Example 7 Following the same procedure as in Example 4 except that a dispersion prepared by dispersing 5 g of a silver paste (No. 4929, made by E. I. du Pont de Nemours and Company) in 2 g of butyl acetate was coated on a PET film of 100 ym thick in a stripe form at a dry coverage of 7 g/m2 (calculated as a silver amount) and the coated film was subjected to a silver chloride-forming treatment (for 120 secs.), an ion selective electrode film pair chip for measuring 4 items was prepared. When the electrodes were connected as shown in Figure 8 and the electrochemical response shown by each ion selective electrode film pair was measured, the same results as In Example 2 were obtained on the 4 items.

Example 8 A silver foil (8 mmx30 mm) of 50 um thick was adhered onto a PET film of 100,um thick using a double side adhesive tape and further polyvinyl chloride adhesive tapes (having a width of 5 mm) were adhered thereon in a stripe form to provide a conductive silver layer-coated film having the same pattern as shown in Figure 1. Then, ion selective layers for 2 items (2 lines for K+ and 2 lines for Na+) were formed on the silver foil in a stripe form and dried to provide an ion selective electrode film for measuring K+ ion and Na+ ion. When the electrodes were connected as in Figure 5 and the electrochemical response was measured and by calculating the concentrations of K+ and Na+ based on the potentials, the values shown in Table 3 were obtained.

Table 3 Conch. of ion (m mol/l) Electrode lncllnation of Measured Verification film pair potential line value value K+ ion 55.4 mV/I-fig.* 7.0 7.2 Na+ ion 54.9 mV/l4ig.* 123.5 125 (*): One figure of concentration This example showed an embodiment of an ion selective electrode film having the structure that the ion selective layer was directly formed on the conductive metal (silver) layer without forming therebetween a water-insoluble metal salt (silver chloride) layer. As is clear from the results of Table 3, it was confirmed that the ion selective electrode film having no water-insoluble metal salt layer provided a normal electrochemical response.

In addition, the inclination of potential line was measured by using an aqueous solution containing K+ ion (1 m mol/l and 10 m mol/l) and Na ion (10 m mol/l and 100 m mol/l) and Versatol as a control liquid, measuring potentials thrice each time on each ion and each concentration, and calculating the inclination of mean potential line by the simple average. By using the value of the inclination, the ion concentration value in Versatol was calculated by the same manner as in Example 2.

Example 9 A mixture of 92 volume parts of indium oxide powder and 8 volume parts of tin oxide powder was subjected to powder sintering at 1 6000C and the oxides were vapor deposited on a PET film of 100 ym thick under heating at vacuum of 5 x 10-5 Torr using the sintered mixture as the evaporation source in the pattern form shown in Figure 1 (at a thickness of 50 nm). The vapor deposited layer was thermally oxidized with oxygen in air by hot blast (for one hour at 150"C). Then, a potassium ion selective layer was formed thereon as in Example 5.

An electrode film pair chip as shown in Figure 2 was made from the potassium ion selective electrode film thus obtained. After connecting the electrode as shown in Figure 5, an aqueous solution containing 5 mol/l of K+ ion as a control liquid and each of aqueous solutions containing 1 m mop/1,10 m mol/l and 100 m mol/l, respectively, as a sample liquid were spotted onto the electrode films and the electromotive force of a potentiometer was measured, thereby a semilogarithmic linear response to the potassium ion was observed. The inclination of the potential line to the potassium ion concentration logarithmic was 55 mV per one figure of potassium ion concentration.

Example 10 Following the same procedure as in Example 5 except that a metal oxide layer was formed by coating a dispersion of 6 g of antimony-doped tin oxide powder (85 mol% tin and 1 5 mol% antimony) dispersed in an aqueous gelatin solution (consisting of 10 g of gelatin and 100 ml of water) on a PET film of 100 ym thick at a dry coverage of 6 g/m2 in the pattern form as shown in Figure 1, a potassium ion selective electrode film only was prepared. When the electromotive force was measured as in Example 9, the inclination of the potential line was 55 mV per one figure of the potassium ion concentration.

Example 11 Following the same procedure as in Example 5 except that 6 g of conductive zinc oxide powder was used in place of the antimony-doped tin oxide powder, a potassium ion selective electrode film was prepared. When the electromotive force was measured as in Example 9, the inclination of the potential line was 56 mV per one figure of the potassium ion concentration.

Example 12 Silver was vapor deposited on a PET film of 100 ym thick in the pattern form shown in Figure 1 (thickness of the silver layer was 7 g/m2). The silver layer was converted into a silver chloride layer at the portions near the surface of the silver layer as in Example 2. Then, by referring to Examples 3 and 40 of Japanese Patent Application (OPI) 142584/77, a dispersion of potassium chloride in polyvinyl alcohol was coated on the silver chloride layer at a dry coverage of 6.5 g/m2 (KCI: 1.5 g/m2 and polyvinyl alcohol: 5.0 g/m2) and dried.

Furthermore, a potassium ion selective layer was formed thereon at a dry coverage of 35.50 g/m2 (polyvinyl chloride (mean polymerization degree of 800): 25 g/m2, Valinomycin: 0.50 g/m2, and didodecyl phthalate: 25 g/m2) in a stripe form to provide a potassium ion selective electrode film. In this case, the ion selective layers were formed in 4 line stripes.

When the potential was measured as in Example 2 and the value was converted into a potassium ion concentration, the same results as in Example 2 per K+ were obtained.

Example 13 In the practical example, ion selective electrode film pair assemblies each for measuring 4 items of K+ ion, Na+ ion, C ion and HCO3- ion were continuously prepared.

A PET film having T-type silver deposited layer and silver chloride layer pattern as shown in Figure 11 A vapor deposited as in Example 1 was fixed on a polystyrene support of 0.5 mm thick. Then, 4 kinds of ion selective layer coating solutions having the same compositions as in Example 2 were coated thereon from nozzles in such manners as covering the leg portions of coupled T patterns as shown by the dotted lines in Figure 11 A at the dry coverage or dry thickness of each ion selective electrode film pairs. In addition, the broad portion of each T pattern was for a terminal portion of electric connection.

Then, a spacer of the shape as shown in Figure 11 B cut from a polyethylene sheet of 0.2 mm thick was supplied and disposed on the electrodes at the position as shown in the figure, then a common bridge of the shape as shown in Figure 11 C cut from a filter paper of 0.4 mm thick was also supplied and disposed at the position as shown in the figure, finally the upper support of the shape as shown in Figure 11 D composed of polyethylene film of 0.4 mm thick was disposed at the position shown in the figure, and two sides having no ion selective electrode film and four corners were welded by the action of ultrasonic wave to provide a desired ion selective pair assembly for 4 items.

The foregoing step was repeatedly performed to provide continuously a number of completed assemblies. The completed assemblies had appearance as shown in Figure 1 2.

When the assemblies described above were electrically connected as shown in the fundamental electric connection mode in Figure 13, a sample liquid and a control liquid were dropped onto the assembly as in Example 2, after 3 minutes the potentials were successively measured by changing over the switch, and each potential value thus obtained was converted into the concentration of each ion; the results coincided well with the assayed value which was obtained on each ion of K+, Na+ and Cl as in Example 2.

Further, for the HCO3- ion, the same results as in Example 2 were obtained.

Example 14 The ion selective electrode film prepared by the same manner as in Example 2 was cut into each single electrode film in a form as shown in Figure 14 as a plane view. The sectional view taken along the line X-Y of each electrode film shown in Figure 14 was almost the same as the structure shown in Figure 15C.

These single electrode films were disposed and fixed on a polystyrene support as shown in Figure 11 A in Example 13 in such a manner that each pair of ion selective electrode films for measuring the same kind of ion were disposed in a line with their terminal portions for electric connection at the opposite sides from each other and with intervals of about 2 mm between the end portions of the ion selective layers thereof. Thereafter, a spacer and a common bridge as shown in Figure 11 B and Figure 11 C, respectively, and an upper support as shown in Figure 11 D were disposed thereon and welded by the action of ultrasonic waves to provide an ion selective electrode film assembly having the same appearance as shown in Figure 12.

When the electrode film assemblies were electrically connected as shown in the fundamental electric connection mode shown in Figure 13, a sample liquid and a control liquid were spotted onto the assembly as in Example 2, after 3 minutes, the potentials were successively measured by changing over the switch, and then the each potential value thus obtained was converted into the concentration of each ion, the same results as in Example 2 were obtained.

By the example, it was confirmed that the ion selective electrode film having the structure that the three edges of the silver layer were covered by the ion selective layer via the silver chloride layer, which is one of the embodiments of this invention, worked normally and could measure correct potential without need of any specific anti-shorting means.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

1. A film-form ion selective electrode comprising a conductive layer and an ion selective layer laminated thereon, said conductive layer being covered by said ion selective layer at least the edge surface thereof.

2. The film-form ion selective electrode as claimed in claim 1 wherein said conductive layer is composed of a conductive metal.

3. The film-form ion selective electrode as claimed in claim 1 wherein said conductive layer is composed of a conductive metal oxide.

4. The film-form ion selective electrode as claimed in claim 2 wherein said electrode further has on said layer of the conductive metal a layer of a water-insoluble salt of the metal as the conductive metal of the conductive metal layer.

5. The film-form ion selective electrode as claimed in claim 4 wherein said electrode further has an electrolyte layer on the layer of the water-insoluble salt of the conductive metal.

6. The film-form ion selective electrode as claimed in claim 1 to 5 wherein said conductive layer is formed on a support.

7. The film-form ion selective electrode as claimed in claims 1 to 6 wherein a part of said conductive layer is not covered by the ion selective layer for functioning as a terminal portion for electric connection.

8. An ion selective electrode assembly for measuring ion concentration comprising a support having an electrically insulating surface having disposed thereon at least a pair of two film-form ion selective electrodes or at least three film-form ion selective electrodes which are disposed adjacent to each other, each of said film-form ion selective electrodes comprising a support having successively formed thereon a conductive layer and an ion selective layer, said conductive layer being covered by the ion selective layer at least the edge surface thereof.

9. The ion selective electrode assembly as claimed in claim 8 wherein the conductive layer is composed of a conductive metal.

10. The ion selective electrode assembly as claimed in claim 9 wherein the conductive layer is composed of a conductive metal oxide.

11. The ion selective electrode assembly as claimed in claim 10 wherein said film-form ion selective electrode further has on the layer of the conductive metal a layer of a water-insoluble salt of the same metal of the conductive metal of the conductive metal layer.

12. The ion selective electrode assembly as claimed in claim 11 wherein said film-form ion selective electrode further has an electrolyte layer on the layer of the water-insoluble salt of the conductive metal.

13. The ion selective electrode assembly as claimed in claims 8 to 12 wherein a part of the conductive layer is not covered by the ion selective layer for functioning as a terminal portion for electric connection.

14. A method of measuring ion concentration or ion activity which comprises applying a sample liquid onto an ion selective layer of a film-form ion selective electrode comprising a conductive layer and the foregoing ion selective layer laminated thereon, said conductive layer being covered by the ion selective layer at least the edge surface thereof, whereby preventing said sample liquid from directly contacting the conductive layer to cause short circuit.

1 5. The method of measuring ion concentration or ion activity as claimed in claim 14 wherein a part of the conductive layer is not covered by the ion selective layer for functioning as a terminal portion for electrical connection.

16. An ion selective electrode and assembly including such electrode(s) substantially as herein described with reference to any one or more of the drawings and Examples.

17. A method of measuring ion concentration substantially as herein described with reference to any one or more of the drawings and Examples.