JPH042902B2 - - Google Patents

Description

〔Technical field〕

The present invention relates to a PH sensor for measuring hydrogen ion concentration in an aqueous solution based on potential response, and particularly to a PH sensor intended for use in biological fluids such as blood and urine. [Prior Art and Problems] Conventionally, glass electrodes have been widely used as sensors for measuring hydrogen ion concentration. However, there are problems such as the glass membrane is easily damaged or contaminated, and there are limits to its use in alkaline solutions. Furthermore, measurement accuracy decreases in a short time in a highly viscous solution or a solution containing an adsorbent substance. In addition, glass electrodes contain an internal reference solution, making it difficult to miniaturize them. For these reasons, electrodes coated with functional polymer membranes are being developed. As an example, JP-A-57-118153 and JP-A-58-65775 disclose a PH sensor in which an electrolytically oxidized polymer membrane of an amino aromatic compound or a hydroxy aromatic compound is adhered to a platinum substrate as a hydrogen ion selectively permeable membrane. Disclosed. This PH sensor uses a platinum wire as the base and does not require an internal reference solution, making it easy to miniaturize.The response speed is also faster than that of glass electrodes, allowing it to be used both in vivo and in vitro. It is. However, this PH sensor has the disadvantage that the equilibrium potential value is easily affected by trace amounts of active ion species, proteins, and sugars present in the aqueous solution to be measured. It has also been found that in measurement solution systems containing oxygen gas or measurement systems in which a large amount of gas is sealed, such as in an oxygenator, the equilibrium potential value of the substrate fluctuates due to the influence of these gases. Additionally, PH sensors have been reported that utilize the principle of glass electrodes and use some kind of liquid film or polymer film instead of the glass film. Among them, a PH sensor using a type of hydrogen ion carrier membrane as a polymer membrane was developed by W. Simon et al. in Analytica Chimica.
Acta, 131, 111 (1981). this
PH sensors do not have an electrode potential that changes depending on the type of electrolyte (standard buffer, serum, plasma, etc.) or body fluid components such as blood, and have a fast response speed. However, as mentioned above, this PH sensor requires an internal reference liquid chamber because it uses the principle of a glass electrode, which makes it difficult to downsize and there is a risk that the internal reference liquid may leak out. There is a problem. Purpose of the invention Therefore, the purpose of the invention is to solve the above-mentioned conventional PH
The object of the present invention is to provide a PH sensor that solves the problems of sensors and can quickly measure PH in an aqueous solution by potential response without being affected by biological fluid components and oxygen. The PH sensor of the present invention is a PH sensor for measuring the hydrogen ion concentration in an aqueous solution by potential response, and includes (a) a conductive substrate, and (b) a reversible substrate formed on the surface of the conductive substrate. (c) a polymer film formed on the surface of the first film; and a second membrane containing a hydrogen ion carrier for transporting hydrogen ions in the aqueous solution to the first membrane. DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, the PH sensor 1 of the present invention
0 includes a conductive substrate 11. Base body 11
Although there is no particular restriction on the shape, a thin line shape is preferable from the viewpoint of miniaturization. The base 11 is made of platinum,
It can be formed from noble metals such as gold and silver, conductive carbon, and the like. Furthermore, a semiconductor material such as indium oxide or tin oxide may be deposited on the surface of the base 11 on which a film having an oxidation-reduction function, which will be described later, is formed. The periphery of the base body 11, except for the tip end surface, is covered with an insulating material 12 such as Teflon. A film 13 having a reversible redox function is adhered to the exposed end surface of the base body 11 . This oxidation-reduction film 13 participates in the oxidation-reduction reaction of hydrogen ions in the aqueous solution to be measured, and therefore accompanies addition and desorption of hydrogen in its own oxidation-reduction reaction. As such a redox film 13, there are those that perform an amine-quinoid type redox reaction and those that perform a quinone-hydroquinone type redox reaction. Examples of compounds that perform amine-quinoid redox reactions include 1-aminopyrene, 1,6
-diaminopyrene, 1,8-diaminopyrene, 1
-aminochrysene, 1,4-diaminochrysene,
1-aminophenanthrene, 9-aminophenanthrene, 9,10-diaminophenanthrene, 1-
Aminoanthracene, p-phenoxyaniline,
o-phenylenediamine, p-chloroaniline,
These include 3,5-dichloroaniline, 2,4,6-trichloroaniline, N-methylaniline, and N-phenyl-p-phenylenediamine. these,
Amines can be represented by the general formula Ar-(NH ₂ )...(). In this formula, Ar represents an aromatic nucleus, such as a benzene nucleus, a naphthalene nucleus, an anthracene nucleus, a pyrene nucleus, a chrysene nucleus, a perylene nucleus,
These include coronene nuclei. These aromatic nuclei may be substituted with an alkyl group, a phenyl group, or the like. Examples of compounds that perform quinone-hydroquinone type redox include 1,6-pyrenequinone,
These include 1,2,5,8-tetrahydroxyquinalizarin, phenanthrenequinone, 1-aminoanthraquinone, purpurin, 1-amino-4-hydroxyanthraquinone, anthralfin, tetrahydroxyatracene, acid black, and the like. These compounds can be represented by the general formula O=Ar=O...(). Here, Ar is an aromatic nucleus similar to that mentioned for the formula. Now, the compound represented by the formula or formula can be directly deposited on the exposed surface of the substrate 11 by electrolytic oxidative polymerization or electrolytic deposition, or by applying electron beam irradiation, light, heat, etc. A film is formed on the exposed surface of the substrate 11 by polymerizing it and dissolving it in a solvent and applying it to the exposed surface of the substrate 11 . Most preferred is a film forming method using electrolytic oxidative polymerization. The oxidation-reduction film 13 described above is dense and blocks the permeation of oxygen molecules in the measurement aqueous solution. However, electrolytes (e.g. urine,
blood, serum, hyperosmolar fluids, and other bioelectrolytes)
If , the electrode potential value fluctuates due to its influence. In addition, there is a problem that the response speed takes more than 5 minutes if the oxidation-reduction film 13 is used alone. Therefore, in the present invention, a hydrogen ion carrier membrane 1 is provided to cover the redox membrane 13 and transport hydrogen ions in the measurement aqueous solution to the redox membrane 13.
4 is formed. This hydrogen ion carrier 1
4 uses a polymer membrane such as polyvinyl chloride as a carrier,
This contains an amine as a hydrogen ion carrier, an electrolyte salt, and, if necessary, a polymer plasticizer. The amine that forms the hydrogen ion carrier has the formula (Here, each of R ¹ , R ² and R ³ is an alkyl group, at least two of which are an alkyl group having 8 to 18 carbon atoms, preferably an alkyl group having 10 to 16 carbon atoms), or the formula (Here, R ⁴ is an alkyl group having 8 to 18 carbon atoms,
Preferably, it is an alkyl group having 10 to 16 carbon atoms. Further, the electrolyte salts forming the hydrogen ion carrier membrane 14 include sodium tetrakis (p-chlorophenyl) borate, sodium tetrakis (p-chlorophenyl) phosphate, potassium tetrakis (p-chlorophenyl) phosphate,
In addition to LiBF ₄ LiPF ₆ and the like, there are compounds represented by the formula R ₄ NBF or R ₄ NPF ₆ (in each formula, R is an alkyl group, preferably an alkyl group having 2 to 6 carbon atoms). Additionally, potassium tetrakis-p-chlorophenylborate may be added to enhance the conductivity of the ion carrier. Furthermore, when the polymer membrane is made of polyvinyl chloride, various plasticizers used as plasticizers for vinyl chloride resin, which are difficult to elute, are used as plasticizers to be added to the hydrogen ion carrier membrane as necessary. Examples include sebacic acid bis(2-ethylhexyl) ester. The polymer used as the carrier is not limited to polyvinyl chloride, but polyethylene and the like that do not require a plasticizer can also be used, but polyvinyl chloride is preferred because it facilitates the formation of a hydrogen ion carrier film. The hydrogen ion carrier membrane 14 is prepared by dissolving the polymer as the carrier in a solvent, adding the amine, electrolyte salt, or a plasticizer if necessary to the solution, and applying this to the redox membrane 13 and drying it. Can be formed. Specific Effects of the Invention In order to measure the hydrogen ion concentration (PH) in an aqueous solution using the PH sensor of the present invention described above, as shown in FIG. It is immersed in a measurement aqueous solution 22 contained in a container 21 together with a reference electrode 23 such as . The PH sensor 10 and the reference electrode 23 are
Connect to potentiometer 24. Hydrogen ions in the aqueous solution are quickly transported to the redox membrane 13 via the hydrogen ion carrier membrane 14, and the redox membrane 13 causes a redox reaction to generate an electromotive force according to the hydrogen ion concentration. This electromotive force is measured as a difference from the reference electrode 23 using a potentiometer 24 . PH of this invention
Since the electromotive force generated by the sensor satisfies a linear relationship with the PH value, the PH of the measured aqueous solution can be determined from this. Examples of this invention will be described below. Example 1 The surface of a disk (diameter 5 mm, height 5 mm) made of basal plain graphite (BPG) was peeled off with a sharp knife to expose a new surface. The outer periphery of this disk substrate was covered with a heat-shrinkable tube to insulate it, mercury was placed inside the tube, and the connection between the substrate and lead wires was planned. Using this as a working electrode, a saturated sodium chloride calomel electrode (SSCE) as a reference electrode, and a platinum mesh as a counter electrode, electrolytic oxidation polymerization was performed in a three-electrode electrolytic cell under the conditions shown below to electrolyze the exposed surface of the substrate. An oxidized polymer film was applied. That is, the electrolyte was prepared by adding 1-aminopyrene (AP) at a rate of 10 mmol/liter and pyridine at a rate of 10 mmol/liter to an acetonitrile solvent containing sodium perchlorate at a rate of 0.1 mole/liter as a supporting electrolyte; After pulling the potential of the working electrode from 0 volts to +1.0 volts (vs. SSCE) three times at a sweep rate of 50 millivolts/sec, constant potential electrolysis was performed for 10 minutes at +1.0 volts (vs. SSCE). I did it. In this way, an electrolytically oxidized polymerized film (oxidation-reduction film) of 1-aminopyrene was deposited on the surface of the substrate. This was thoroughly washed with water and stored in a phosphate buffer solution of pH 6.86 for one day to stabilize the redox potential of the redox membrane. After drying this, a hydrogen ion carrier film was applied by the following method. 25.6 milligrams of tri-n-dodecylamine, 5.7 milligrams of potassium tetrakis-p-chlorophenylborate, and dioctyl sebacate.
732 mg, polyvinyl chloride (average degree of polymerization
1050) was dissolved in 10 milliliters of tetrahydrofuran, and the substrate coated with the redox film was immersed in this solution, and the solvent was removed and dried to deposit a hydrogen ion carrier film on the redox film. In this way, the PH sensor of this invention was produced. Experimental Examples 1 to 6 Using the PH sensor obtained in Example 1, the relationship between the equilibrium potential value of the sensor and PH in various solutions was measured using SSCE as a reference electrode. That is, the solutions used were bovine blood (Experimental Example 1), standard serum (Versatol A, General Giagotics der Werner
- Lambert) (Experimental Example 2), Lactated Ringer's solution (components: sodium chloride 0.6% (w/v), potassium chloride 0.03% (w/v), lactic acid 0.31% (w/v),
Electrolyte components are Nal31mg/, K4mg/, Ca3mg/
, Cl110mg/, lactic acid root 28mg/) (Experimental Example 3),
0.1=M/5% dextran in saline
(w/v) (Experiment Example 4), bioelectrolyte auxiliary solution {Terumo High Calcium Solution, ingredients:
Glucose, potassium acetate, calcium gluconate, magnesium sulfate, KH ₂ PO ₄ , ZnSO ₄ 7H ₂ O,
Electrolyte ions K ⁺ (25 mg), Mg ⁺ (8.5 mg), Ca ²⁺ (150
mg), SO ^2- ₄ (10 μmol)} (Experiment Example 5), and artificial urine (Urine Control manufactured by URSure Chemistry).
1) (Experimental Example 6). The results are shown in Figure 3 (Experiment Example 1), Figure 4 (Experiment Examples 2 and 5 (match)), and Figure 5.
It is shown in the figure (Experimental Examples 3 and 4 (match)). Experimental Example 7 Using the PH sensor prepared in Example 1, adjust the pH from 5.34 to 4.67, from 7.46 to 5.34, and 4.67 in phosphate buffer.
from 6.27, from 6.27 to 8.16, from 8.16 to 9.18, from 9.18
10.02, 10.02 to 11.0, 11.0 to 12.0, 12.0 to
The response time (time taken to reach equilibrium potential value) when changing to 13.0 was measured (temperature 25°C). The results were extremely fast, ranging from 20 seconds to 2 minutes, as shown by lines a to i in Figure 6. Also, the electrode potential is 8
It remained stable with no change even after several days had passed. Experimental Example 8 The electromotive force change value per PH of the PH electrode prepared in Example 1, that is, the slope of the Nernst equation linear relationship (mV/PH) was measured by changing the temperature of the solution. For comparison, we also measured the gradient between a glass electrode and a PH sensor that does not form a hydrogen ion transport membrane (comparative example). The results are shown in Table 1. From this result, it was found that the slopes of the PH sensor of the present invention and the glass electrode are almost the same, and that the PH sensor of the present invention can be used in a measurement system used with a glass electrode.

[Table] Experimental example 9 Using the PH sensor produced in Example 1, PH6.86
Oxygen partial pressure in standard phosphate buffer from 47 mmHg
The influence of oxygen partial pressure on the equilibrium potential value was measured by varying it within a range of 630 mmHg. Measured temperature is 37°±0.1
It was warm at ℃. The results are shown in FIG. This result shows that the PH sensor of the present invention is not affected by oxygen at all. Example 2 When producing a redox membrane, PH was carried out in the same manner as in Example 1 except that tetrabutylammonium BF ₄ was used instead of sodium perchlorate as the supporting electrolyte.
A sensor was created. Experimental Example 10 When the relationship between the electromotive force and PH of the PH sensor produced in Example 2 was measured (at 37°C), a linear relationship was satisfied. The slope of this straight line was 58 mV/PH. Note that the electromotive force value at pH 7.4 was approximately 40 mV. Examples 3 to 4 Carbon fiber (HTA-7W manufactured by Toho Rayon Co., Ltd.) was used instead of basal plain graphite.
−100, specific resistance approximately 1.5×10 ^-3 Ω・cm, cross-sectional area 3.8×
10 ^-4 cm ² ) was used in the same manner as in Example 1.
A sensor was produced (Example 3). In addition, a PH sensor was similarly produced using BPG with a diameter of 0.5 mm (Example 4). Experimental Example 11 When the relationship between the equilibrium potential value and the PH value was measured for the PH sensors produced in Examples 3 and 4, each satisfied a linear relationship, and the slopes of the straight lines were 62 mV/PH and 60 mV/PH, respectively. It was hot. Among the other solutions used in Experimental Examples 1 to 6, the pH
We were able to perform measurements. Example 5 A PH sensor was produced in the same manner as in Example 1 except that 1-aminoanthracene was used instead of 1-aminopyrene. Experimental example 12 Equilibrium potential value of the PH sensor prepared in Example 5 and
When the relationship with PH was measured, a linear relationship was satisfied. The slope of this straight line was 56 mV/PH in the PH range of 5.15 to 8.20. Examples 6-7 Same as Example 1 except that trioctylamine (Example 6) or tridecylamine (Example 7) was used instead of tri-n-dodecylamine when depositing the hydrogen ion transport membrane. A PH sensor was fabricated using the following method. Experimental Example 13 When the relationship between the equilibrium potential value and the PH value of the PH sensors produced in Examples 6 and 7 was measured, a linear relationship was satisfied. The slopes of both lines were 56 mV/PH. Note that the linear relationship was also satisfied when artificial urine was used instead of the phosphate buffer as the measurement solution. Examples 8 to 11 Instead of BPG as a substrate, platinum (Example 8),
A PH sensor was produced in the same manner as in Example 1, except that palladium (Example 9), indium oxide (Example 10), and silver (Example 11) were used and electrolytic oxidative polymerization was performed under the conditions shown in Table 2. did.

[Table] Experimental Example 14 When the relationship between the equilibrium potential value and the PH value of the PH sensors produced in Examples 8 to 11 was measured (at 25°C), a linear relationship was satisfied for each. Table 3 shows the slope of the straight line and other results.

[Table] Example 12 A PH sensor was produced in the same manner as in Example 1, except that sodium sulfate or sulfuric acid at a concentration of 0.5M containing 10mM of p-phenoxyaniline was used as the electrolytic solution during electrolytic oxidative polymerization. Experimental example 15 Equilibrium potential value of the PH sensor prepared in Example 12 and
When the relationship with the PH value was measured, a linear relationship was satisfied, and the slope of the straight line was 54 mV/PH. In addition, the equilibrium potential value at PH6.86 is approximately 62mV,
The response speed was about 1 minute. Examples 13 to 32 PH electrodes were produced in the same manner as in Example 1, except that AP was electrolytically polymerized under the conditions shown in Table 4.

【table】

[Table] Experimental Examples 16 to 35 Using the PH sensors produced in Examples 13 to 32, the influence of oxygen partial pressure (PO ₂ ) and standard serum (Versatol) on the equilibrium potential value was investigated. We also measured the response speed around PH=7.0. The results are shown in Table 5. Based on this result, the relationship between the amount of pyridine added and ΔE (E value under saturated oxygen partial pressure minus E value under dissolved oxygen partial pressure in the atmosphere) in the electrolytic oxidative polymerization of AP is shown in Figures 8 and 9. As shown in the figure. The white circles in Figure 8 correspond to Experimental Examples 16 to 20, and the black circles correspond to Experimental Examples 21 to 20.
Equivalent to 25. Line a in FIG. 9 corresponds to Experimental Examples 26 to 30, and line b corresponds to Experimental Examples 31 to 35. As a result, TBAF ₄ −THF system>TBABF ₄ −CH ₃ CN>
It was found that the ΔE was smaller in the order of NaClO ₄ -THF system > NaClO ₄ -CH ₃ CN system, and the system was stable against oxygen partial pressure in this order. Furthermore, the relationship between the difference between the E value in the standard serum and the E value in the standard solution (phosphate buffer) and the amount of pyridine added is shown in FIGS. 10 and 11. In Figure 10, line a corresponds to experimental examples 16 to 20, and line b corresponds to experimental examples 16 to 20.
Equivalent to 21-25. The middle line a in Fig. 11 indicates Experimental Example 26~
30, and line b corresponds to Experimental Examples 31-35. From this result, the above difference is the NaClO ₄ −CH ₃ CN system＞
TBABF ₄ −CH ₃ CN series＞TBABF ₄ −THF series＞
It can be seen that the NaClO ₄ -TF system is smaller in order. Furthermore, it can be seen that when TBABF ₄ is used as the supporting salt, the above difference does not depend on the amount of pyridine added and becomes a substantially constant value. Note that the response speed is NAClO ₄ −THF
The order is system> _NaClO4 - _CH3CN system> _TBABF4 - _CH3CN system> _TBABF4 -THF system.

[Table] Specific Effects of the Invention As stated above, the PH sensor of the present invention is a solid-state electrode, so it can be easily miniaturized, has a fast response speed, is not affected by gas components, especially oxygen gas, and is suitable for living organisms. The accuracy is high because the equilibrium potential value does not change depending on the type of component sample, such as serum, whole blood, or urea.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the PH sensor of this invention, Figure 2 is a cross-sectional view of the PH sensor of this invention.
The figure is a diagram for explaining the action of the PH sensor of the present invention, and Figures 3 to 11 are graphs showing the characteristics of the PH sensor of the present invention. 11... Conductive substrate, 12... Redox film, 13...
Hydrogen ion carrier membrane.

Claims (1)

[Scope of Claims] 1. A PH sensor for measuring hydrogen ion concentration in an aqueous solution based on potential response, comprising: (a) a conductive base; and (b) a reversible base formed on the surface of the conductive base. (c) a first film having a redox function, the redox reaction of which involves the addition and desorption of hydrogen ions; and (c) a polymer film formed on the surface of the first film. and a second membrane containing a hydrogen ion carrier for transporting hydrogen ions in the aqueous solution to the first membrane.