JPH0331223B2 - - Google Patents

Description

〔Technical field〕

This invention relates to a reference electrode. [Prior art and problems] Conventionally, hydrogen electrodes, calomel electrodes, silver/silver chloride electrodes, etc. have been mainly used as reference electrodes, but there are many cases where electrodes are miniaturized or used in the medical field. In this case, in a reference electrode equipped with a reference liquid chamber, the reference liquid may mix with the sample solution, or the internal liquid may leak due to temperature changes in the measurement solution, and the reference liquid chamber itself is a major obstacle in the design of electrode miniaturization. This results in various inconveniences. In order to solve these problems, the present applicant has proposed a method for applying halides (mainly silver halide) on the surface of a conductor (mainly silver) or supported on the conductor in Japanese Patent Application No. 56-206095.
A reference electrode was proposed in which at least one polymer film (a polymer film derived from hydroxyaromatic compounds) was deposited directly on the surface of the layer. In addition, as a solution to the problem of silver elution during the deposition of a polymer film in this reference electrode, Japanese Patent Application No. 134883/1983 describes the use of a polymer compound containing coordinating nitrogen atoms and silver on the surface of a conductive substrate. An application has been filed for a reference electrode comprising a polymer silver complex layer formed of a complex with ions or mixed with silver halide. However, it has been found that even with this reference electrode, silver ions and silver chloride ions are eluted into the measurement solution during use, resulting in a tendency for the electromotive force to decrease. OBJECT OF THE INVENTION Therefore, the object of the present invention is to provide a reference electrode that retains the advantage of the membrane-coated reference electrode described above in that it can be miniaturized, and also solves the problem of elution of silver ions and silver chloride ions during use. Our goal is to provide the following. According to this invention, a polymeric silver complex layer consisting of a complex of a polymeric compound containing a coordinating nitrogen atom and silver ions or a mixture of silver halide with the polymeric compound containing a coordinating nitrogen atom is formed on the surface of a conductive substrate. A reference electrode is formed by forming an ion conductive film containing an anionic compound covering this polymeric silver complex layer. At least the surface of the conductive substrate is composed of silver or silver halide supported on silver. Examples of the polymer compound containing a coordinating nitrogen atom include polyacrylamide, polymethacrylamide, polyvinylamine, polyacrylonitrile, and polymethacrylonitrile. Examples of anionic compounds include polystyrene sulfonic acid, polyacrylic acid, polymethacrylic acid, and poly(perfluorosulfonic acid). In a preferred embodiment of the present invention, the ion conductive membrane extends from the polymeric silver complex layer, and its tip constitutes the portion to be brought into contact with the measurement sample solution. That is, in this preferred embodiment, only the ion-conducting membrane of the reference electrode of the present invention comes into contact with the measurement sample solution, thereby eliminating the influence of interfering ions (particularly chloride ions). DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings. As shown in FIG. 1, the reference electrode of the present invention has a layer 1 formed of a complex of a polymer compound containing coordinating nitrogen atoms and silver ions on the surface of a conductive substrate 11.
2 is attached. Conductive substrate 11
At least its surface is made of silver (i.e., it is made entirely of silver, or a thin silver film is deposited on another conductive substrate by sputtering, etc.)
It is preferable. Furthermore, a thin silver film may be formed on the surface of a nonconductor such as a Teflon tube. It is convenient to use an electrolytic oxidation method to deposit the polymeric silver complex layer 12 on the substrate 11 whose at least the surface is made of silver. That is, first, the surface of the substrate 11 is polished to make it smooth, washed with water, washed with methanol, and then dried. For electrolysis, a normal three-electrode cell was used, with this substrate as the working electrode and a platinum wire mesh as the counter electrode, using a sodium chloride saturated calomel electrode (SSCE).
is the reference electrode. As the electrolytic solution, a solution containing a coordinating nitrogen-containing polymer compound and a supporting electrolyte is used. When electrolysis is carried out under these conditions, silver on the surface of the substrate is oxidized and eluted, forms a complex with a polymer compound in the electrolytic solution, and a layer of the polymer silver complex is deposited on the surface of the substrate. in this case,
The surface of the substrate turns reddish-brown due to the coloring reaction unique to polymeric silver complexes, and the formation of a polymeric silver complex layer can be confirmed. This complex layer is a viscous film. In this way, a strong polymer silver complex layer 12 is formed on the surface of the substrate 11. Examples of the polymer compound containing a nitrogen atom capable of coordinating with silver ions include polyacrylamide, polymethacrylamide, polyvinylamine, polyacrylonitrile, and polymethacrylonitrile. Moreover, in order to form the polymer silver complex layer 12,
Silver nitrate or the like may be added to the solution of the polymer compound to form a complex, and this may be applied to the surface of the substrate 11 and dried. The polymeric silver complex layer may contain silver halide (particularly silver chloride) therein. Further, the surface of the conductive substrate 11 may be formed of silver halide supported on silver. In order to incorporate silver halide into the polymer silver complex layer, silver halide (particularly silver chloride) is added to the coating solution containing the polymer silver complex, and the solution is coated and dried in the same manner. Also,
In order to form a silver halide layer on the surface of a conductive substrate, the silver surface of the conductive substrate is brought into contact with a halogen, particularly chlorine. A polymer silver complex layer is formed on this silver halide layer by the coating method described above. Alternatively, a polymer silver complex layer containing silver chloride can be formed on a conductive substrate by performing electrolytic oxidation using the electrolytic oxidation method described above using an electrolytic solution containing sodium chloride as a supporting electrolyte. In addition,
The base 11 may be made of a conductive adhesive containing silver or the like. Alternatively, a polymer silver complex or a mixture thereof mixed with silver halide may be formed into a film in advance, and this film may be integrated onto a conductive substrate using an adhesive (for example, an epoxy resin). A reference electrode can be obtained even if the Furthermore, an ion permeable membrane may be interposed between the surface of the conductive substrate 11 and the polymer silver complex layer. As such an ion permeable membrane, a cellulose resin membrane, a hydroxy aromatic compound polymer, a vinyl polymer (including a cross-type polymer), etc. can be used. Note that in the case of a polymer silver complex containing silver chloride or a reference electrode having a silver chloride layer on the conductor surface, interfering ions (especially
A polymer membrane that can stably immobilize _chloride ions can be used as a membrane to prevent the permeation of _chloride ions. Polyvinylpyridine having a molecular weight of 7200 is quaternized with methylene chloride to a degree of quaternization of 90% (hereinafter referred to as QPVP), which is preferably formed on the polymer silver complex layer. In this case, since chloride ions exist relatively stably in QPVP, it shows a stable equilibrium potential value over a wide PH range. Now, an ion conductive film 13 made of an anionic compound is formed on the polymer silver complex layer 12 in order to prevent elution of silver ions or silver chloride during pH measurement, for example. Examples of anionic compounds include polyanions such as polystyrene sulfonic acid, polyacrylic acid, polymethacrylic acid, and poly(perfluorosulfonic acid). Poly(perfluorosulfonic acid) is commercially available, for example, from DuPont under the trade name Nafion. These anionic compounds form ion complexes with silver ions to prevent their elution and quickly conduct hydrogen ions to the electrode sensitive area. Furthermore, if there are interfering ions (especially chloride ions) at a concentration that affects the electromotive potential in an electrolyte solution such as a pH measurement solution, the ion conductive membrane 13 has the role of blocking the permeation of such interfering ions. fulfill The reference electrode is surrounded by an insulating layer 1 such as Teflon.
Cover with 4. The reference electrode of the embodiment shown in FIG. 2 is of a type in which, even if the above-mentioned interfering ions are present in the pH measurement sample liquid, the electromotive potential is not affected by these interfering ions. This reference electrode has a substrate in which a silver layer is formed by tightly winding a silver wire 22 around a non-conductive tube 21, such as a Teflon tube, leaving a tip end. This silver layer may carry a silver chloride layer as described with respect to FIG. The above-mentioned polymer silver complex layer 12 is formed to cover the entire silver layer. The previously described ion conductive layer 1 extends from the tip of this polymer silver complex layer 12 to the tip of the nonconductor tube 21.
3 is formed. The entire periphery of this structure is an insulating heat-shrinkable plastic tube 14'.
covered and fixed. Ion conductive layer 13
The tip surface 13a of is exposed. When the reference electrode shown in Figure 2 is immersed in a pH measurement sample solution, even if interfering ions, especially chlorine ions, are present in the sample solution, the electrode sensitive area (covering the silver layer) Because there is a distance L to the polymer silver complex), interfering ions are difficult to propagate to the electrode sensitive part and are not easily affected by it. Note that hydrogen ions travel through the ion conductive layer 13 much faster than chlorine ions and reach the electrode sensitive portion. The distance L is
It is preferably about 0.1 mm to 25 mm. Specific effects of the invention Using the reference electrode of this invention, for example,
When measuring PH, as in the past, measure this at an appropriate PH.
The PH value is determined by immersing the electrode in the measurement solution and reading the electromotive force between the two electrodes with a potentiometer. Example 1 A silver wire was tightly wound around a Teflon tube with an outer diameter of 1.0 mm to obtain a silver layer with a thickness of about 0.15 mm. (When forming silver chloride on the surface of this silver layer, immerse this silver wire-coated tube in a 0.1M sodium chloride aqueous solution and electrolyze at a current density of 0.25 mA/cm ² for 30 minutes to form a silver chloride layer on the surface of the silver layer.) formed). On the other hand, silver nitrate was added to a dimethylformamide solution containing polyacrylonitrile (PAN) at a concentration of 3% by weight to form a PAN-silver complex. On the other hand,
After the silver layer or silver chloride layer was immersed in a silver nitrate saturated methanol solution, the PAN-silver complex solution was cast thereon. This operation was repeated several times to form a PAN-silver complex layer with a thickness of 0.01 mm. next,
On this PAN-silver complex layer, a thickness of 0.14 mm, a width of 3 mm,
Wrap the Nafion tape with a length of 100mm and the thickness
It was formed to 0.28 mm and fixed with a heat-shrinkable plastic tube. In this way, a reference electrode having the structure shown in FIG. 2 was obtained. Note that the periphery of this electrode was fixed with an epoxy adhesive. The following experiment was conducted using this reference electrode. Note that L in this reference electrode was 10 mm. Experiment 1 A commercially available saturated sodium chloride calomel electrode (SSCE) and the above reference electrode were immersed in a 50mM phosphate buffer (sample solution) whose pH was changed using sodium hydroxide and perchloric acid. The equilibrium potential value and response speed (time taken to reach the equilibrium potential value) during that time were investigated. In this case, the experiment was conducted twice: when the reference electrode was immersed from the tip 13a to a point corresponding to the center of the polymer silver complex layer (A), and when only the vicinity of the tip 13a was immersed (B). Ta. The results are shown in Table 1.

[Table] As a result, it can be seen that even if the pH of the measurement solution is changed, the equilibrium potential value does not change, and the electrode of the present invention operates as a reference electrode. Furthermore, it is hardly affected by the immersion position of the reference electrode during measurement. Experiment 2 Platinum was sputtered onto the exposed tip of a stainless steel wire whose surroundings were covered with Teflon, and phenol and 1,2
A PH sensor was obtained by immersing the membrane in a methanol solution containing diaminobenzene and performing electrolytic oxidative polymerization to form an electrolytic oxidative copolymer film of phenol and 1,2-diaminobenzene on the platinum membrane. Example 1
Using this PH sensor as a reference electrode, the relationship between the equilibrium potential value between both electrodes and PH was investigated in the same measurement solution as in Experimental Example 1 (measurement temperature: 25°C).
The results are shown by straight line a in FIG. The slope of this straight line is
It was 59mV/PH. Moreover, the response speed was about 3 minutes. From the above results, it was found that the electrode of the present invention can be used as a reference electrode when measuring solution PH based on electrode potential response. Example 2 A reference electrode having the same structure as in Example 1 was prepared, except that a QPVP film was formed on the PAN-silver complex layer and a 0.5% dimethyl sulfoxide solution of naphion was applied thereon. Phosphoric acid buffer solution (PH
This reference electrode and SSCE were immersed in 6.86), and the relationship between the equilibrium potential value and the chloride ion concentration was investigated. The results are shown in Figure 4. As is clear from this result, the equilibrium potential value was almost constant (460 mV) even when chloride ions were present up to 10 ^-1 M/. The operation was exactly the same as in Experimental Example 2 except that this reference electrode was used. The results are shown by straight line b in FIG. The slope of this straight line was 59 mV/PH. Example 3 An experiment was conducted in rabbit arterial blood using the blood circulation circuit shown in FIG. Blood from the rabbit artery enters drip tube 31 through line L ₁ and from there to heat exchanger 32 through line L ₂ .
The blood leaving the heat exchanger 32 enters the gas exchanger 33 through line L ₃ where carbon dioxide gas is added. Blood exiting the gas exchanger 33 reaches the flow cell 35 through line L ₄ and branch line L ₅ . This flow cell 35 has a blood flow path 3 in the lateral direction.
5a, and reaches this flow path to form an electrode insertion hole 35.
b is provided. A reference electrode and a PH sensor are inserted into this electrode insertion hole 35b, and both are connected to a potentiometer 36. flow cell 35
The blood that exits passes through line _L6 and joins the blood in line _L4 in line _L7 . A dissolved carbon dioxide measuring meter 34 is provided in the middle of the line _L4 . On the other hand, the blood coming out of the drip tube 31 is sent to a branch line.
It is also diverted to L ₈ , passing through line L ₉ from the drip tube 37,
It merges with the blood that has passed through line L ₇ and forms line L _10.
It is returned to the rabbit vein through the rabbit vein. This blood circulation is performed by a pump P provided within the line _L2 . The reference electrode used was the one produced in Example 1, and the PH sensor was the one produced in Experimental Example 2, with a polycarbonate film formed on the surface by a casting method. Further, the carbon dioxide gas introduction rate was 5 ml/min, and the blood flow rate was about 22 ml/min. The results are shown in Table 2.

[Table] When the relationship between the equilibrium potential value and the PH value obtained here was plotted, a straight line C in FIG. 3 was obtained, and the slope of this straight line was 54 mV/PH. Specific Effects of the Invention As described above, the reference electrode of the present invention has a simple structure in which a film is formed on a conductive substrate, and there is no need to provide a reference liquid chamber, so it can be miniaturized. Furthermore, even if there are interfering ions, especially chlorine ions, in the measurement sample liquid, the device operates stably without being affected by them.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic configuration of a reference electrode of the present invention, FIG. 2 is a partially sectional side view showing a reference electrode according to a preferred embodiment of the invention, and FIGS. 3 and 4 are a reference electrode of the present invention. FIG. 5 is a block diagram showing a blood circulation circuit used in measuring the characteristics of the reference electrode of the present invention. 11, 22... Conductive substrate, 12... Polymer -
Silver complex layer, 13... ion conductive layer.

Claims (1)

[Scope of Claims] 1. A polymeric silver complex layer consisting of a complex of a polymeric compound containing a coordinating nitrogen atom and silver ions, or a mixture of silver halide with the polymeric compound containing a coordinating nitrogen atom, is formed on the surface of a conductive substrate. A reference electrode is formed by forming an ion conductive film containing an anionic compound and covering the polymer silver complex layer. 2. The reference electrode according to claim 1, wherein the ion-conductive membrane extends from the polymeric silver complex layer, and the tip thereof constitutes the part to be in contact with the measurement sample solution.