JPS62150150A - Ph sensor - Google Patents

Abstract

PURPOSE:To measure electromotive force of a sensor accurately, by applying hydrogen ion carrier film on the surface of a stick shape conductive substrate. CONSTITUTION:A copper wire 2 is fixed on the bottom surface 1a of a cylindrical BPG 1 with a conductive bond 3 and the wire 2 and the BPG 1 are coated with a Teflon paint 4 to insulate. Then, tip surface and circumferential surface of the BPG 1 are cut out and an oxide polymer film 5 is applied direct on the expose surface on the BPG 1 at the tip thereof to make a oxidation/ reduction film electrode. This electrode is dipped into a hydrogen ion carrier composition and dried repeatedly to apply a hydrogen ion carrier film 6. The electric film resistance of this film 6 shall be 50MOMEGA at 10 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a PL sensor, more specifically a PL sensor, which has a fast response speed and stable operation even at low temperatures of around 10°C.
Regarding H sensor.

[Conventional technology and its problems]

Membrane-coated solid electrodes can be miniaturized and do not have internal liquid chambers, so unlike electrodes with internal liquid chambers, there is no risk of internal liquid leaking outside and contaminating the metal being tested, making them suitable for medical sensors. Attention has been paid.

One of the flexibility of membrane-coated solid electrodes for practical use is their high response speed. Generally, response speed tends to be inversely proportional to film thickness. Polyvinyl chloride (PVC)
In a solid electrode coated with an ion carrier film containing an ion carrier material in a polymer, when the film thickness is large, the electrode film resistance shows a high value of 100 MΩ or more. However, if the hydrogen ion carrier film is thin, the sensor characteristics deteriorate in a short period of time, making it impractical. Therefore, the optimal film thickness is 0.8~1
．． It is about 2u, and the membrane resistance at this time is 70 to 100M.
becomes Ω. The membrane resistance increases by 2 when the temperature decreases by 10℃.
This is a problem especially when measuring at low temperatures. The present inventor found that when the electrode membrane resistance exceeds 50 MΩ, noise increases and it becomes difficult to accurately measure the electromotive force of the pH sensor.

One way to reduce membrane resistance is to increase the electrode area, but if the electrode rkJ product is increased, the electrode itself must also be increased.

However, ■Measurement is possible with a small amount of test liquid;■
Considering the requirements for clinical testing, such as being sensitive to temperature changes and being able to directly measure pH in body fluids using a catheter, etc., it is essential that the pH sensor be small.

Small sensors are considered to be highly sensitive to temperature changes because their electrodes have a small heat capacity and the temperature reaches equilibrium in a short time even if there is a sudden change in the temperature of the test liquid.

[Means for solving problems]

As a result of intensive studies aimed at miniaturizing a pH sensor consisting of a membrane-covered solid electrode in which the electrode membrane resistance of a hydrogen ion carrier membrane is 50 MΩ or less even at 10°C, the present inventors discovered that a stick-shaped pH sensor as a conductive substrate was used as a conductive substrate. The present invention has been completed based on the discovery that the above object can be achieved by applying a film not only to the tip surface but also to the outer peripheral surface of the metal.

That is, the present invention is characterized in that a hydrogen ion carrier film is coated on the surface of a stick-shaped conductive substrate, which is formed by coating a pattern having a reversible redox function on the outer peripheral surface or the outer curved surface and the tip surface. It is a pH sensor.

Further, it is desirable that the hydrogen ion carrier membrane used in the present invention has an electrode membrane resistance of 50 MΩ or less at 10°C.

Examples of the conductive substrate used in the pH sensor of the present invention include basal plane pyrolytic graphite (basal plane pyrolytic graphite).
graphite (hereinafter referred to as BPG), conductive carbon materials such as glassy carbon; metals such as gold, platinum, copper, silver, palladium, nickel, and iron, especially noble metals, or those containing indium oxide, tin oxide, etc. on the surface of these metals. Examples include those coated with a semiconductor. Among these, conductive carbon materials are preferred, and BPG is particularly preferred. In order to make the pH sensor small, a stick-like conductive substrate is used.
A film containing a reversible redox function is deposited on 20-.

If the area is smaller than this, the electrode membrane resistance of the hydrogen ion carrier membrane will exceed 50 MΩ at 10° C., which is undesirable, and if it is larger, the pH sensor will not be compact. The stick may be cylindrical or prismatic, but a cylindrical stick with a rounded tip is particularly preferred in terms of moldability and film breakability. Conventionally, BPG
The basal plane has mainly been used as an electrode surface.

However, the present inventors have discovered that the edge surfaces of BPG can also be effectively used to produce scales, and therefore stick-shaped electrodes can be produced even with BPG. BPG is particularly superior in terms of stability of sensor operation. For example, in the case of a cylindrical stick, BPG sticks have a diameter of 061 to 2 from the viewpoint of strength.
Preferably a dragon.

In addition, a film having a reversible redox function (hereinafter sometimes referred to as a redox film) means that an electrode formed by adhering this film to the surface of a conductive substrate is applied to a conductive substrate at a constant potential through a reversible redox reaction. In the present invention, it is particularly preferable to use a material whose potential does not vary depending on the oxygen gas partial pressure. Examples of such a redox film include: (1) an organic compound film or polymer film capable of carrying out a quinone-hydroquinone type redox reaction, and (2) an organic compound film or polymer film capable of carrying out an amine-quinoid redox reaction. etc. are mentioned as suitable ones. Here, the quinone-hydroquinone type redox reaction refers to, for example, one expressed by the following reaction formula, taking the case of a polymer as an example.

(In the formula, R1 and R2 represent, for example, a compound with an aromatic-containing structure.) In addition, the amine-quinoid type redox reaction is expressed, for example, by the following reaction formula, taking the case of a polymer as described above. say something

(In the formula, R3 and R4 represent, for example, a compound having an aromatic-containing structure.) Examples of compounds that can form a film having such a reversible redox function include the following compounds (a) to (C). Can be mentioned.

(In the formula, Ar is an aromatic nucleus, each R5 is a substituent, m is the effective valence number of 1 to Ar, and n2 is O to Ar.

A hydroxy aromatic compound represented by the effective valence number -1'Ik). Even if the aromatic nucleus of Ar is a monocyclic one, such as a benzene nucleus,
anthracene nucleus, pyrene nucleus, chrysene nucleus, perylene nucleus,
It may be a polycyclic nucleus such as a coronene nucleus, and may be a heterocyclic nucleus as well as a benzene nucleus.

As the substituent R5, for example, an alkyl group such as a methyl group,
Examples thereof include an aryl group such as a phenyl group, and a nitrogen atom. Specifically, for example, dimethylphenol,
Phenol, hydroxyquirin, O-4 bamboo m-benzyl alcohol, 0-lm- or p-hydroxybenzaldehyde, 0- or m-hydroxyacetophenone, 0-1m- or p-hydroxypropiophenone,
0-lm- or p-pentsuphenol o-1m-4
or p-hydroxybenzophenone, 0-lm- or p-carboxyphenol, diphenylphenol, 2
-Methyl-8-hydroxyquinoline, 5-hydroxy-
1,4-naphthoquinone, 4-(p-hydroxyphenyl)2-butanone, x, s-1 hydroxy-1,2,3,
4-tetrahydronaphthalene, bisphenol A1 salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, 1,8-dihydroxyanthraquinone, 5
-hydroxy-1,4-naphthoquinone and the like.

(b) The following formula (wherein, Ar is an aromatic nucleus, each R6 is a substituent, m is the effective valence number of 1 to Ar2, and n is 0 to Ar.

As the aromatic nucleus and substituent R6 of the amine aromatic compound Ar, which indicates the effective valence number of -1), the same ones as Ar, and the substituent R'' in the compound (&) are used, respectively. Specific examples of amine aromatic compounds are listed below.
Aminophenanthrene, 9-aminophenanthrene, 9
．． 10-diamino7enanthrene, 1-aminoanthraquinone, p-phenoxyaniline, O-phenylenediamine, p-chloroaniline, 3.5-dichloroaniline, 2,4.6-drichloroaniline, N-)f-ruaniline, N -phenyl-p-phenylenediamine and the like.

C) Quinones such as 1.6-pyrenequinone, 1.2,5.8-tetrahydroxynarizarin, phenanthrenequinone, 1-aminoanthraquinone, purpurin, 1-amino-4-hydroxyanthraquinone, and anthralphine.

Among these compounds, especially 2,6-xylenol, 1
-Aminopyrene is preferred.

Further, as compounds that can form the redox film according to the present invention, d) poly(N-methylaniline) [Jinsen, Senshu, Koyama, Journal of the Chemical Society of Japan, 1801-1809 (1984):
l, poly(2,6-dimethyl-1,4-)unilene ether), poly(0-)unilene diamine), poly(phenol), polyxylenol; fi polymer of pyrazoquinone vinyl monomer, isoalloxazine vinyl monomer An organic compound containing the compounds (a) to (C) of a quinone-based vinyl polymer condensation compound such as a polymer,
The redox reaction of compounds (a) to (c) with low polymerization degree (oligomer), or (a) to (C) (r) fixed to a high molecular compound such as a polyvinyl compound or a polyamide compound. Examples include those with gender.

Note that in this specification, the term polymer includes both homopolymers and interpolymers such as copolymers.

In order to deposit a compound capable of forming a redox film on the surface of a conductive substrate, an amine aromatic compound, a hydroxy aromatic compound, etc. is deposited on the substrate surface by an electrolytic oxidation polymerization method or a dissociation deposition method. A method of direct polymerization, or a method of dissolving a pre-synthesized polymer in a solvent by applying electron beam irradiation, light, heat, etc., and fixing this solution to the substrate surface by dipping/coating and drying; A method can be adopted in which the substrate is directly fixed to the surface of the substrate by chemical treatment, physical treatment, or irradiation treatment.

Among these methods, the X decomposition polymerization method is particularly preferred.

The electrolytic oxidative polymerization method is carried out by electrolytically oxidizing and polymerizing an amine aromatic compound, a hydroxy aromatic compound, etc. in a solvent in the presence of a suitable supporting electrolyte to deposit a polymer film on the surface of a conductor. Examples of the solvent include acetonitrile, water, dimethylformamide, dimethyl sulfoxide, propylene carbonate, methanol, etc., and examples of the supporting electrolyte include sodium perchlorate, sulfuric acid, disodium sulfate, phosphoric acid, boric acid, and tetrachloride. Preferred examples include potassium fluorophosphate and quaternary ammonium salts. In electrolysis, selection of electrolysis temperature is extremely important in obtaining a good redox film. That is, the present inventors have found that the electrolytically oxidized polymer membrane of 2,6-dimethylphenol has different properties depending on the electrolysis temperature. The redox film is -5 to -3
It is preferable to form the film at 5° C., so that a dense and extremely stable film is formed, and an electrode that can be used for a long period of time in a high temperature region can be produced. Therefore, the sensor of the present invention having a redox film obtained by electrolytic oxidative polymerization in this temperature range operates stably in a wide temperature range of 10 to 45°C.

The thickness of the redox film is preferably 0.1 μm-015111. If it is thinner than 0.1 μm, the effect of the present invention will not be sufficiently achieved, and if it is thicker than 0.5 nm, the membrane resistance will become too high, which is not preferable in terms of measurement.

Further, the redox film can be used by impregnating it with TM material. Examples of 't11f* include dipotassium hydrogen phosphate, sodium perchlorate, sulfuric acid, tetrafluoroborate, and tetraphenylborate. A simple method for impregnating the redox membrane with an electrolyte is to attach the redox membrane to a conductive substrate and then immerse it in an electrolyte solution.

The hydrogen ion carrier film that is further deposited on the surface of the redox film deposited on the conductive substrate as described above is
A membrane in which a hydrogen ion carrier substance and, if necessary, an electrolyte salt are supported on a polymer compound is used.

As a hydrogen ion carrier substance, the following formula (where R,
, R, and Ro are the same or different and represent an alkyl group, at least two of which represent an alkyl group having 8 to 18 carbon atoms, and amines represented by the following formula (wherein, R4 to 18 alkyl groups), and a preferred one is tri-n-dodecylamine.

In addition, examples of the polymer compound include vinyl chloride resin,
Examples include vinyl chloride-ethylene copolymer, polyester, polyacrylamide, polyurethane, silicone resin, etc., and those from which plasticizers do not easily elute are used. Examples of such plasticizers include dioctyl sebacate, dioctyl adipate, dioctyl maleate, di-n-octylphenylphosphonate, and the like. Moreover, tetrahydrofuran is preferably used as the solvent.

In order to deposit a hydrogen ion carrier film on the surface of a redox film, for example, 50 to 500 parts by weight of a plasticizer and 0.1 to 50 parts by weight of a hydrogen ion carrier substance are added to 100 parts by weight of a polymer compound as a carrier. parts and electrolyte salts etc. in a solvent (
For example, the base electrode (in this case, the redox film-coated electrode) is immersed in a solution dissolved in Tetrahydro7ran), pulled up, air-dried, and then dried (80°C, 3 minutes) about 30 times to obtain a carrier film thickness of 50 μm to 3 ml. ! It is particularly preferable to set the distance between 0.3 and 2 degrees. Alternatively, paste vinyl chloride, hydrogen ion carrier material, plasticizer,
After mixing the electrolyte salt in the above weight ratio, the substrate was placed on top of the plate to a thickness of 50 μm to 3 cm, and heated at 150°C for 1 hour.
A hydrogen ion carrier film can also be obtained by heating for a minute to form a gel. The hydrogen ion carrier film deposited in this manner has, for example, a resistance of 10 3 to 10 5 Ω at 25° C. when the film is 1 mm thick. In addition, the influence of dissolved oxygen and other coexisting substances in the test liquid can be effectively prevented.

〔Effect of the invention〕

Since the pH sensor of the present invention has the above-mentioned configuration, it has a relatively large surface area even though it is extremely small, and can be used at 10°C, which is required for use.
The electrode membrane resistance of the hydrogen ion carrier membrane could be reduced to 50 MΩ or less, making it possible to perform measurements at low temperatures.

For a sensor, being small is extremely important not only in terms of clinical testing requirements, but also in terms of its versatility, and also means that it responds sensitively to changes in the temperature of the sample liquid.

In addition, the sensor of the present invention, which is coated with a film that is difficult to dissolve in plasticizer obtained by electrolytic oxidation polymerization at a specific temperature, works stably even when used at high temperatures in combination with the above effects. It can be used in a wide temperature range of ~45°C, and is extremely advantageous in practice.

〔Example〕

Next, an example will be given and explained.

Example 1 A sensor of the present invention (FIG. 1) was produced according to the following method.

(1) Preparation of redox membrane electrode A cylindrical (diameter 1.01 x length 3.5 ut) basal plain pyrolytic graphite (BPG,
Bottom surface; basal surface, outer lI! d side; edge side) 10 Fix the lead wire 2 of copper wire (0,2 5i6) to the circular bottom 1a with conductive adhesive (manufactured by Amicon, C-850-6) 3, and then attach the lead wire 2 and BPG were coated with Teflon paint (Toughcoat ■ manufactured by Daikin Industries, Ltd.) 4 for insulation.

Next, cut out the tip surface and outer circumferential surface of BPG to obtain BPG.
ii.The oxidized polymer film 5 was directly applied by electrolytic oxidation under the following conditions. B.P.
A redox film electrode was prepared by coating the exposed surface of G (film thickness: 3
0μm).

(Electrolyte composition) 0.5M2.6-xylenol and 0.2M NaCAO
An acetonitrile solution of No. 4 was used.

(Electrolytic oxidation conditions) BPG was polarized, saturated sodium chloride calomel electrode (
5SCE) was used as a reference electrode, and a platinum wire mesh was used as a counter electrode.

In electrolytic oxidation, the electrolytic polymerization temperature is kept constant at -19.5℃,
Change the electrolytic voltage from 0 volts (vs. 5 SCE, hereinafter the same) to 1.
After scanning up to 5 volts three times at a sweep rate of 50 mV/sec, constant potential electrolysis was performed at 1.5 volts for 10 minutes.

(2) Deposition of hydrogen ion carrier membrane The redox membrane battery obtained in (1) was repeatedly immersed and dried in a hydrogen ion carrier composition having the following composition to deposit a hydrogen ion carrier membrane 6 on it. The dipping and drying process was repeated 15 times to ensure that the hydrogen ion carrier film of Otnttr uniformly covered the surface of the redox film.

(Hydrogen ion carrier composition) Tridodecylamine 2 volumes/
ml polyvinyl chloride (pn=1050) 6
5.6 Rashikat Dioctyl sebacate (DO8)
131.2 shells/rat tetrahydrofuran (TI(
F)'i was used as a solvent.

Examples 2 to 4 In Example 1, a square column (vertical o, s
mt x compensation 0.9 silk x length 2 positive), thin plate type (length 1.3
A pH sensor was produced in the same manner as in Example 1, except that a material (2 mtx, 0.3 mx thick, 2 mtx long) was used. In both cases, the BPG substrate was designed so that the tip surface was an edge surface.

Example 5 Using the pH sensor gold produced in Examples 1 to 4, the electromotive force for 5SCE was measured in a phosphate buffer, and the electromotive force was plotted against pH (hereinafter referred to as Nernst plot). The slope of this Nernst plot and the selectivity coefficient Ki ("Na+") of each pH sensor for Na ion to Po were measured. In addition, a pH Senbu with a disk-shaped BPG substrate (only the basal surface was used) was used as a comparative product. The results are shown in Table 1.

Table 1 Example 6 (1) The membrane resistance of the pH sensor obtained in Example 1 at each temperature was investigated.

Table 2 below * Table 2, which is the same as the comparative product of Example 5, shows that the membrane resistance approximately doubles for every 10° C. temperature decrease. In addition, in the case of a disk type example, the resistance exceeds 50 MΩ at low temperatures.

(2) Using the above two types of pH sensors, α force (relative to 5SCE) was measured in the standard solution in the same manner as in Example 5. The measurement was performed at a temperature of the standard solution in the range of 10 to 45°C. A differential electrometer was used to measure the electromotive force to reduce common mode noise.

As a result, with the fixed type, the noise is ±0.0 at all temperatures.
Although it was within 2 mV and caused no trouble in measurement, the disk type had noise of ±0.5 mV or more at temperatures below 20° C., making it difficult to accurately measure the electromotive force.

Reference Example 1 A redox membrane electrode was prepared in the same manner as in Example 1 (1) except that the electrolytic polymerization temperature was variously changed, and the obtained membrane had a DO8
The solubility in the oxidation-reduction film was immersed in a DO3 solution at 121° C. for 8 hours, and then the presence or absence of the film and the change in color of the DO8 solution were examined. The results are shown in Table 3.

As shown in Table 3 of the third moat, the membrane electropolymerized at -20.5℃ is D
It is found that the film is insoluble in O8 and is extremely stable even at high temperatures. Therefore, in order to obtain a pH sensor that operates stably for a long period of time at high temperatures (for example, 45°C), it is necessary to carry out electrolytic polymerization at around -20°C.

[Brief explanation of drawings]

FIG. 1 shows a schematic vertical cross-sectional view of an example of the pH sensor of the present invention. Above is Figure 1 RPC 1a bottom 2 Lead wire 3 Conductive adhesive 4 Teflon paint 5 Oxidized polymer film 6 Water accumulated ion carrier film

Claims (1)

[Scope of Claims] 1. A hydrogen ion carrier film is coated on the surface of a stick-shaped conductive substrate which has a film having a reversible redox function coated on the outer peripheral surface or the outer curved surface and the tip surface. A pH sensor featuring: 2. The p according to claim 1, wherein the hydrogen ion carrier membrane has an electrode membrane resistance of 50 MΩ or less at 10°C.
H sensor. 3. The pH according to claim 1, wherein the conductive substrate is basal plain pyrolytic graphite.
sensor. 4. The membrane having a reversible redox function is a polymeric membrane that performs a quinone-hydroquinone type redox reaction, and the membrane has a reversible redox function of 0 to -
The pH sensor according to claim 1, which is obtained by electrolytic oxidative polymerization at a temperature of 100°C.