JPH0453381B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention uses a chemical substance-sensitive sensor consisting of an electrode selectively sensitive to chemical substances and a liquid junction type reference electrode to detect chemical substances in a liquid to be measured. It relates to a device for measuring quantities. More specifically, the present invention relates to an ultra-small device for measuring chemical substances in which a sensor and a reference electrode are housed in a single thin tube. (Prior art and its problems) In recent years, in the fields of physiology and medicine, substances in body fluids represented by blood, such as ions such as hydrogen, sodium, potassium, calcium, and chlorine, oxygen, gases such as carbon dioxide, glucose, sugars such as lactose,
Concentration measurements of chemical substances such as hormones, enzymes, and antibodies have become more frequent. Conventionally, various types of electrodes, such as glass electrodes and coated-wire electrodes, have been used to measure the concentration of such chemical substances.
Among them, glass electrodes are made by changing the composition of the glass film,
It is widely used because it can be made into an electrode that is selectively sensitive to various chemical substances by coating a chemically sensitive film on a glass film. Recently, as an ultra-compact ion sensor, JP-A-51
Ion sensors using the electric field effect of semiconductors were proposed in publications such as No.-139289 and No. 54-66194. This ion sensor is an ISFET (Ion Sensitive Field
It is called "Effect Transistor". Since the ISFET can be miniaturized, it is attracting attention as a biological monitoring sensor that is inserted into living tissue to measure the amount of chemical substances in the living body. When measuring the ion concentration of a test liquid with this ion sensor, the circuit shown in FIG. 1 is usually used. That is, the ISFET 1 is immersed together with the liquid junction type reference electrode 4 in the liquid to be measured 8 in the container 6, and the ISFET
A positive potential of a voltage source Vd is connected to the drain 2 of the circuit, and a constant current circuit 5 is connected to the source 3 of the circuit to operate as a source follower circuit. Then, a change in the conductivity of the channel under the gate insulating film due to a change in the interfacial potential between the gate insulating film 7 of the ISFET and the liquid to be measured 8 is converted into a change in the source potential Vs and extracted. Since this source potential Vs has a linear relationship with the logarithm of the ion concentration, the ion concentration of the test liquid can be measured by measuring this Vs. The above ISFET or conventional glass electrode
In order to measure the amount of chemical substances in a liquid to be measured using a chemical substance measurement electrode such as a coated-wire electrode, a reference electrode that has a constant potential with the liquid regardless of the composition of the liquid to be measured is required. It is absolutely necessary.
For this reason, the reference electrode has a structure in which the liquid to be measured and an internal liquid of a certain composition contained in the tube come into contact through a narrow space called a liquid junction provided at the tip of the sealed tube. The internal liquid inside the tube
Internal electrodes such as Ag-AgCl electrodes are immersed. In particular, the reference electrode that is housed in a single tube together with a small ion sensor that can be sterilized in an autoclave, such as an ISFET for biological monitoring, must be ultra-small and can be sterilized in an autoclave together with the electrode for measuring chemical substances. Must be. The applicant of this application developed a reference electrode in which the internal solution was gelled with a polymer as a reference electrode for use with small electrodes for measuring chemical substances such as ISFETs.
Proposed in No. 204363. Such a reference electrode includes one tube, an internal liquid gelled with 2 to 10 wt% polyvinyl alcohol and 0.1 to 2 wt% titanium compound housed inside the tube, and an internal electrode immersed in the internal liquid. and a liquid junction provided at the tip of the tube that communicates the inside and outside of the tube. However, subsequent studies revealed that the comparative electrode using the above-mentioned specific polymer gel as an internal solution holder still had the following various problems. (1) During storage or high-pressure steam sterilization, the bubbles contained in the polymer gel aggregate to form large bubbles that block the inside of the tube, causing the liquid junction between the internal electrode and the external liquid to be measured to break. be done. (2) When a polymer gel is used as an internal liquid holder, the liquid junction potential difference is large, and therefore the potential of the reference electrode varies depending on the components of the test liquid. (3) Manufacturing the reference electrode is complicated because a polymer and a crosslinking agent are placed inside the reference electrode and gelled. (Means for Solving the Problems) Therefore, an object of the present invention is to house a chemical substance sensitive sensor consisting of an electrode selectively sensitive to a specific chemical substance and a liquid junction type comparison electrode in one tube. An object of the present invention is to provide a device for measuring chemical substances that can be sterilized using high-pressure steam. A chemical substance measuring device for measuring the amount of a chemical substance in a liquid to be measured according to the present invention is a chemical substance measuring device for measuring the amount of a chemical substance in a liquid to be measured. A tubular body both having two cavities, and an electrode selectively sensitive to a specific chemical substance housed in one cavity of the tubular body with a chemical substance measurement region protruding from an end of the tubular body. a lead wire having one end connected to the electrode, the other end extending along the cavity, and connected to a connector at the other end opening of the tubular body, and filling at least the lead wire connection portion of the electrode. A chemical substance sensitive sensor made of an electrically insulating resin that closes the cavity and a pore volume accommodated at the tip of the other cavity of the tubular body.
A porous filament having a hydrophilicity of at least 0.2 cc/g and at least a hydrophilic surface, housed in the cavity such that one end is in contact with the filament, and extending along the cavity. The silver-silver chloride wire is connected to the connector at the other end opening of the cavity, and at least the tip of the cavity is filled to contact and fix the silver-silver chloride wire and the filament, and the cavity is closed. an electrically insulating resin that obstructs;
This device for measuring chemical substances is characterized by being constructed with a liquid junction type reference electrode made of an internal liquid that is suctioned and held by a porous filament. A water-resistant material is used for the tubular body having at least two independent cavities. Generally, polyamides such as nylon 6, nylon 11, and nylon 12, polyesters, polypropylene, polyvinyl chloride resins, and rubber resins such as silicone rubber, urethane rubber, and polyisoprene rubber are used. Porous filaments with hydrophilic surfaces include polyvinyl alcohol, ethylene vinyl alcohol copolymer, polyhydroxyethyl methacrylate, and those obtained by reacting each of these polymers with glutaraldehyde, formaldehyde, etc., or polyacetyl cellulose, A filament made of a hydrophilic polymer such as polyacrylonitrile, or a porous filament made of a hydrophobic polymer such as polypropylene, polytetrafluoroethylene, polyethylene, polystyrene, polysulfone, etc., whose surface has been made hydrophilic is used. be able to. Examples of hydrophilic treatment include chemical treatment such as sulfonation, and treatment with ethanol, surfactants, and the like. It is necessary to make the porous filament made of a hydrophobic polymer hydrophilic to such an extent that water is naturally drawn into its pores by capillary action. In addition, the porous filament has a large pore volume in order to suck and retain the internal solution.
It must have a porosity of 0.2cc/g or more. If the pore volume is less than 0.2 cc/g, the internal solution retention capacity will be insufficient and the internal resistance of the reference electrode will become too large, which is not preferable. The pore volume in the present invention is a value obtained by dividing the total pore volume (cc) measured by a mercury porosimetry porosimeter by the sample weight (g). The filament may be a monofilament, a multifilament, a staple fiber, used singly, in the form of a bundle or a twisted filament, or in the form of a hollow fiber. The above filament has micropores with an average diameter of 0.01 to 10μ arranged almost uniformly in the cross section, and the diameter in the range of 0.01 to 10μ gradually or continuously from the surface of the fiber to the inside or in the opposite direction. It may have a variation in size, or it may have an extremely thin skin layer on its surface. When the pore diameter of the micropores becomes 10 μ or more, the mechanical strength of the porous filament decreases, and the diffusion of chlorine ions in the internal solution becomes faster. potential tends to drift. On the other hand, when the pore diameter is 0.01 μm or less, the diffusion of ions in the internal solution becomes too slow and the internal resistance of the reference electrode becomes large, resulting in large induced noise. In order to miniaturize the reference electrode, it is preferable that the outer diameter of the filament is as small as possible. The hollow fibers used usually have an outer diameter of 50 to 3000μ and a film thickness of 10 to 500μ. The above-mentioned porous filamentous body can be manufactured by conventional spinning techniques. For example, polyvinyl alcohol-based porous hollow fibers can be produced by the method described in JP-A-52-21420. In addition, porous hollow fibers of polysulfone are disclosed in Japanese Patent Application Laid-Open No. 58-91822.
It can be produced by the method described in No. By these methods, porous hollow fibers that have sufficient heat resistance and mechanical strength and whose elution amount of potassium permanganate reducing substances during high-pressure steam sterilization is less than the permissible amount are continuously manufactured. be able to. The filamentous body is housed within the opening at the tip of the cavity provided in the tubular body. In this case, it is preferable that the filamentous body is housed in the cavity so that its tip end is substantially the same as the tip of the tubular body. If the length of the filament inserted into the cavity is short, the internal liquid sucked and held by the filament will diffuse out into the test liquid, so it is necessary to make the length such that the internal liquid does not diffuse out. This length can be appropriately determined depending on the shape of the filament. Diameter as thread
When using a filament of 0.3 mm, the insertion length into the cavity is usually preferably 1.5 cm or more. When hollow fibers are used as the filament, it is preferable to close the hollow portion by inserting a porous monofilament or the like into the opening at the tip of the hollow fiber or over the entire area of the hollow portion. When using hollow fibers with an inner diameter of 50μ or less, if the distance between the tip of the silver monochloride wire and the liquid junction is set to 2 cm or more, rapid changes in the chloride ion concentration of the internal solution can be prevented without clogging the hollow part. That is, rapid changes in the silver-silver chloride electrode potential can be suppressed. The tip of the silver-silver chloride wire housed in the cavity must be in contact with the filament. This silver-silver chloride wire extends along the cavity and is connected to a connector at the other end opening of the cavity. When using a short silver-silver chloride wire, the silver-silver chloride wire is brought into contact with the filament, a lead wire is connected to the end of the wire, and the lead wire is extended along the cavity to open the cavity. The other end may be opened to connect to a connector. As the electrically insulating resin that contacts and fixes the silver-silver chloride wire and the filamentous body and closes at least the tip of the cavity, epoxy resin or silicone resin may be used alone, or both may be used in combination. It's okay. The internal fluid sucked and retained by the filamentous body is often a saturated KCl solution for normal PH measurements, but in the medical field, especially for measuring body fluids such as blood, an appropriate internal fluid composition must be selected. It won't happen. Conditions for the internal liquid include the following. (1) No liquid junction potential difference will occur. The liquid junction potential difference becomes smaller as the mobilities of positive and negative ions moving through the liquid junction where the test liquid and the filamentous body are equal are equal. To achieve this condition, use ions with equal mobility for positive and negative ions in the internal solution.
Moreover, it is better to make its concentration higher than that of the sample liquid. Examples of electrolytes in which positive and negative ions have equal mobility include KCl and NH ₄ Cl. (2) Does not contain ions to which the ion sensor responds. If the ion activity to be measured in the test liquid changes due to the internal liquid flowing out from the filamentous body, an error will naturally occur. (3) It should not react with the test liquid and have little harmful effect on living organisms. When measured in blood, the outflow of K ⁺ ions is harmful to living organisms. If the internal fluid is more concentrated than the blood, the difference in osmotic pressure will cause blood cells to contract,
Protein coagulation occurs. On the other hand, if the internal fluid is more dilute than blood, there are problems such as swelling of blood cells. For example, when measuring the pH of the internal fluid in the stomach, the pH changes are large and accuracy is not required, so we decided to allow some error due to the liquid junction potential.
A 0.5M KCl solution is used. On the other hand, when measuring PH in blood, it is necessary to prevent the outflow of K ⁺ ions, and in order to equalize the osmotic pressure of blood, it is necessary to use physiological saline (0.15M), which is close to its components.
NaCl solution) is used. Although there is a difference in the mobility of Na ⁺ and Cl ^- , the salt concentration of blood is approximately 0.15M NaCl
Since it is close to , no liquid junction potential difference occurs. Before use, the reference electrode is immersed in the internal liquid so that the filament attracts and retains the internal liquid. In this case, the suction of internal fluid into the filament is
This is usually achieved by natural suction into the pores by capillary action. Next, the chemical substance measuring device of the present invention will be explained with reference to the drawings. FIG. 2 is a sectional view of the chemical substance measuring device of the present invention. In Figure 2, it is used as an electrode sensitive to chemical substances.
An example using ISFET is shown. In this device, a tubular body having at least two independent cavities, for example, a double lumen catheter 10 is used. ISFET at the tip of one cavity of the catheter
A gate portion 11 is made to protrude from the catheter, and its electrode portion is embedded and fixed in a water-resistant electrically insulating resin 12 that closes the opening at the distal end of the cavity. Applicable
A lead wire 13 connected to the electrode portion of the ISFET extends along the cavity and is connected to a connector 14 at the other end opening of the catheter. On the other hand, a porous hollow fiber 15 is accommodated at the tip of the other cavity of the catheter. There is silver in the space of this hollow fiber.
One end of the silver chloride wire 16 is inserted. The silver
A silver chloride wire extends along the cavity and is connected to a connector 14 at the other end of the catheter. In this figure, porous hollow fibers are used, and silver is inserted into the hollow part of the hollow fibers from the tip opening of the hollow fibers.
Since the length L to the tip of the silver chloride wire is sufficiently long, the opening at the tip of the hollow fiber is not blocked. Further, the cavity within the catheter is filled with electrically insulating resin 17. To provide a device that can measure a plurality of chemical substances with one device by using a tubular body having three or more independent cavities and accommodating one of the ISFETs each sensitive to a different chemical substance in each cavity. Can be done. Reference numeral 18 denotes a guard electrode that connects the liquid to be measured and the source follower circuit in order to remove AC induced disturbances of the ISFET and perform accurate measurements. When using an ISFET, the value of the source potential changes, making accurate measurement of ion concentration difficult, mainly due to AC induction disturbances such as indoor AC wiring or AC leaking through the floor entering the sensor circuit via the ground wire. be. Especially high impedance,
For example, if a small liquid junction type reference electrode of 100 KΩ or more is used or the drain current is 30 μA or less, the above-mentioned alternating current induction disturbance is large and measurement is difficult. When the guide electrode is connected to an isolation circuit, external signals, mainly alternating current, flowing through the living body do not flow to the sensor circuit, so accurate measurements can always be performed. A conductive metal wire such as platinum or silver is used as this guard electrode, and is housed in the cavity together with the ISFET. A lead connected to the guard electrode extends along the cavity and is connected to a connector at the other end of the catheter. (Effect of the invention) In the above reference electrode, the internal solution (chloride ion-containing electrolyte solution) is retained in the pores of the porous thread, the porous thread is in close contact with the silver-silver chloride electrode, and Since it extends to the liquid junction, even if it is extremely small, it is impossible for the liquid junction between the silver-silver chloride electrode and the liquid to be measured to be broken. Furthermore, even if air bubbles enter the space formed at the contact area between the silver-silver chloride wire and the filament, the filament that retains the internal liquid in its pores will be in close contact with the silver-silver chloride wire at one end, and at the other end. Since the liquid junction is in contact with the liquid to be measured, conduction between the silver-silver chloride electrode and the liquid to be measured is always maintained. Since the internal liquid is retained in the pores of the porous filament by capillarity, disconnection of conduction is extremely unlikely to occur. Furthermore, even if multiple small bubbles are generated within the pore, each bubble is prevented from moving by the pore wall, so the conduction between the silver-silver chloride electrode and the liquid to be measured is interrupted. It will not grow into a large bubble. Since the above reference electrode uses a porous filament prepared in advance as an internal solution holder, it is extremely easy to assemble the reference electrode housed in the tubular body together with the sensor for measuring chemical substances. Furthermore, since porous yarns are mass-produced using spinning technology, those with uniform performance can be easily obtained. Furthermore, if a porous filament is used as an internal liquid retainer, for unknown reasons,
It has also been found that the liquid junction potential difference is smaller than when a polymer gel is used, and therefore the error as a reference electrode is reduced. Especially when hydrophilic polymer sols or gels are used as internal fluid carriers, especially in solutions containing borates (e.g. 9.18PH buffer),
However, when a porous filament is used as an internal liquid retainer, this abnormal voltage is reduced to 3 mV.
The following is true. (Example) Example 1 First, porous PVA hollow fibers were prepared using Japanese Patent Application Laid-Open No. 52-21420.
Manufactured by the method of No. The obtained polyvinyl alcohol hollow fibers had an outer diameter of 0.3 mm and an inner diameter of 0.05 mm. When the cross section of this hollow fiber was observed with an electron microscope, it was found that it was 0.02 to 2μ.
The micropores were uniformly arranged in the cross section. Pore volume determined by mercury porosimeter is 0.23
It was cc/g. The hollow fiber was cut into a length of 30 mm and adhered to a silver-silver chloride wire with a diameter of 0.15 mm to assemble a comparison electrode as shown in FIG. In FIG. 3, 21 is the polyvinyl alcohol porous hollow fiber, 22 is a silver-silver chloride wire, and 23 is an epoxy resin for bonding the two. On the other hand, a PH sensor using ISFET as shown in Fig. 4 was assembled as follows. The ISFET 24 to which the lead wire 26 is bonded and the guard electrode 25 are connected to a nylon tube 28 with an inner diameter of 0.5 mm and an outer diameter of 0.6 mm.
It was pulled inside and fixed with insulating resin 27. Next, the reference electrode shown in Fig. 3 and the PH sensor shown in Fig. 4 were embedded in a silicone rubber double lumen having two cavities with inner diameters of 0.3 mm and 0.5 mm to produce the composite PH sensor shown in Fig. 5. 29 in Figure 5
is a silicone rubber double lumen, and 30 is a connector. The tip of the composite PH sensor was immersed in physiological saline, and the saline was naturally drawn into the hollow fibers by capillary action. Using the composite PH sensor manufactured in this way, the PH of the following eight types of solutions was measured at 37°C. 0.050M Potassium Hydrogen Phthalate 0.050M Potassium Hydrogen Phthalate, 0.154M NaCl, 0.025M
KH ₂ PO ₄ , 0.025M Na ₂ HPO ₄ , 0.025M KH ₂
PO ₄ , 0.025M Na ₂ HPO ₄ , 0.154M NaCl,
0.009M KH ₂ PO ₄ , 0.030M Na ₂ HPO ₄ ,
0.009M KH ₂ PO ₄ , 0.030M Na ₂ HPO ₄ , 0.154M
_{NaCl ,} 0.010M _Na2B4O7 , _{0.010M Na2B4
O7} , 0.154M NaCl. The results are shown in Table 1. As is clear from Table 1
For solutions containing NaCl (,,,),
The PH electrode of the present invention and the commercially available glass electrode display the same PH value. NaCl-free solution (,,,
), the PH electrode of the present invention displays a PH value about 0.05 PH higher than that of a commercially available glass electrode. Even after high-pressure steam sterilization of the PH electrode, no break in conduction of the internal liquid of the reference electrode was observed. Furthermore, even when the PH electrode thus obtained was left at room temperature for 10 minutes and air bubbles were intentionally mixed into the internal space of the hollow fiber of the reference electrode, no change was observed in the performance or stability of the reference electrode. . Dip the 10cm tip of these 10 PH electrodes into 30ml of water.
After heating at 121℃ for 30 minutes,
The internal solution was taken out and subjected to eluate test, sterility test, acute toxicity test, pyrogenic substance test, hemolytic test, and skin reaction test, and it passed all tests. Comparative Example 1 A third electrode was used instead of the reference electrode shown in FIG.
A device consisting only of the silver-silver chloride wire 22 and epoxy resin 23 shown in the figure (without hollow fibers) was made, and this and the PH sensor shown in FIG. 4 were embedded in the same silicone double lumen as in the example, and the Composite PH like
Created an electrode. Then PVA inside the reference electrode
Instead of the hollow fibers, an aqueous solution containing 5% by weight of polyvinyl alcohol and 0.5% by weight of titanium acetylacetonate was injected and allowed to stand at room temperature for 16 hours to gel. Table 1 summarizes the results of measuring the PH of the solutions described in Example 1 using the composite PH electrode thus obtained. As is clear from this result
A composite PH sensor that uses PVA gel as the internal liquid of the reference electrode has almost accurate PH for solutions containing NaCl.
gives the value, but for solutions without NaCl
Gives an error of 0.10PH or more. In addition, solutions containing borate (,) cause large measurement errors regardless of the presence or absence of NaCl. The composite PH electrode is placed in the air.
When the gel was left to stand for 10 minutes and the water in the internal solution of the reference electrode was intentionally evaporated, it was confirmed that the gel shrank and voids were created within the reference electrode. When the PH of the solution described in Example 1 was measured using this PH electrode, the displayed PH value fluctuated between 6.4 and 6.9. Comparative Example 2 As the porous hollow fiber in Example 1, the outer diameter was 0.3
Example 1 Using polyvinyl alcohol-based porous hollow fibers with
A composite PH electrode was created in the same manner. the compound
When I tried to measure the PH of the solution using a PH electrode, the displayed PH value fluctuated between 6.6 and 6.8. 【table】

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram for measuring the amount of a chemical substance in a liquid to be measured using a chemical substance measuring device consisting of a chemical substance sensitive sensor using an ISFET as an electrode and a liquid junction type comparison electrode. FIG. 2 is a sectional view of the chemical substance measuring device of the present invention. 3 and 4 are cross-sectional views of a comparison electrode and a sensor used in the present invention. FIG. 5 is a sectional view of a chemical substance measuring device in which the reference electrode and sensor of FIGS. 3 and 4 are housed in a double lumen catheter.

Claims (1)

[Scope of Claims] 1. A chemical substance measuring device that measures the amount of a chemical substance in a liquid to be measured, the chemical substance measuring device comprising:
a tubular body having at least two independent cavities;
An electrode that is selectively sensitive to a specific chemical substance is housed in one cavity of the tubular body with a chemical substance measurement region protruding from the end of the tubular body, and an electrode that is selectively sensitive to a specific chemical substance is housed in one cavity of the tubular body, and another electrode is connected to the electrode at one end. A lead wire whose end extends along the cavity and is connected to a connector at the other end opening of the tubular body, and an electrically insulating resin which fills at least the lead wire connection portion of the electrode and closes the cavity. a chemical substance sensitive sensor, and a pore volume accommodated in the tip of the other cavity of the tubular body is 0.2 cc/g or more,
and a porous filament whose surface is at least hydrophilic; one end of the porous filament is housed in the cavity so as to be in contact with the filament, and the other end of the cavity is opened by extending along the cavity. a silver-silver chloride wire connected to the connector, and a silver-silver chloride wire filled in at least the tip of the cavity.
It is characterized by comprising a liquid junction type reference electrode consisting of an electrically insulating resin that contacts and fixes the silver chloride wire and the filament and closes the cavity, and an internal liquid that is sucked and held by the porous filament. Equipment for measuring chemical substances. 2 Electrodes that are selectively sensitive to specific chemical substances,
2. The device of claim 1, which is an ion-sensitive field effect transistor with a sensor gate. 3 Electrodes that are selectively sensitive to specific chemical substances,
2. The device of claim 1, which is an ion-sensitive field effect transistor having a plurality of sensor gates selectively sensitive to different chemicals. 4. The device according to claim 1, wherein a plurality of electrodes selectively sensitive to different chemical substances are respectively housed in one of the cavities provided in the tubular body. 5. The device according to claim 1, wherein the porous filament is a filament made of a hydrophilic polymer. 6. The device according to claim 1, wherein the porous filament is a hollow fiber, and a tip end of a silver-silver chloride wire is inserted and fixed into the hollow portion of the hollow fiber. 7. Claim 1, wherein the porous hollow fibers are hollow fibers having a membrane thickness of 10 to 500 μm and in which micropores with an average pore diameter of 0.02 to 2 μm are substantially uniformly arranged in the cross section. The device described.